PRE
TEST
®
Clinical Vignettes
for the USMLE Step 1
PreTest® Self-Assessment and Review
Notice
Medicine is an ever-changing science. As new research and clinical experience
broaden our knowledge, changes in treatment and drug therapy are required. The
authors and the publisher of this work have checked with sources believed to be
reliable in their efforts to provide information that is complete and generally in
accord with the standards accepted at the time of publication. However, in view of
the possibility of human error or changes in medical sciences, neither the authors
nor the publisher nor any other party who has been involved in the preparation or
publication of this work warrants that the information contained herein is in every
respect accurate or complete, and they disclaim all responsibility for any errors or
omissions or for the results obtained from use of the information contained in this
work. Readers are encouraged to confirm the information contained herein with
other sources. For example and in particular, readers are advised to check the product information sheet included in the package of each drug they plan to administer
to be certain that the information contained in this work is accurate and that
changes have not been made in the recommended dose or in the contraindications
for administration. This recommendation is of particular importance in connection
with new or infrequently used drugs.
PRE
TEST
®
Clinical Vignettes
for the USMLE Step 1
PreTest® Self-Assessment and Review
Second Edition
McGraw-Hill
Medical Publishing Division
New York Chicago San Francisco Lisbon London Madrid Mexico City
Milan New Delhi San Juan Seoul Singapore Sydney Toronto
Copyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved. Manufactured in the United States of
America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher.
0-07-141814-8
The material in this eBook also appears in the print version of this title: 0-07-137376-4
All trademarks are trademarks of their respective owners. Rather than put a trademark symbol after every occurrence of a trademarked name, we use names in an editorial fashion only, and to the benefit of the trademark owner,
with no intention of infringement of the trademark. Where such designations appear in this book, they have been
printed with initial caps.
McGraw-Hill eBooks are available at special quantity discounts to use as premiums and sales promotions, or for
use in corporate training programs. For more information, please contact George Hoare, Special Sales, at
george_hoare@mcgraw-hill.com or (212) 904-4069.
TERMS OF USE
This is a copyrighted work and The McGraw-Hill Companies, Inc. (“McGraw-Hill”) and its licensors reserve all
rights in and to the work. Use of this work is subject to these terms. Except as permitted under the Copyright Act
of 1976 and the right to store and retrieve one copy of the work, you may not decompile, disassemble, reverse engineer, reproduce, modify, create derivative works based upon, transmit, distribute, disseminate, sell, publish or sublicense the work or any part of it without McGraw-Hill’s prior consent. You may use the work for your own noncommercial and personal use; any other use of the work is strictly prohibited. Your right to use the work may be
terminated if you fail to comply with these terms.
THE WORK IS PROVIDED “AS IS”. McGRAW-HILL AND ITS LICENSORS MAKE NO GUARANTEES OR
WARRANTIES AS TO THE ACCURACY, ADEQUACY OR COMPLETENESS OF OR RESULTS TO BE
OBTAINED FROM USING THE WORK, INCLUDING ANY INFORMATION THAT CAN BE ACCESSED
THROUGH THE WORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIM ANY WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. McGraw-Hill and its licensors do not warrant
or guarantee that the functions contained in the work will meet your requirements or that its operation will be uninterrupted or error free. Neither McGraw-Hill nor its licensors shall be liable to you or anyone else for any inaccuracy, error or omission, regardless of cause, in the work or for any damages resulting therefrom. McGraw-Hill has
no responsibility for the content of any information accessed through the work. Under no circumstances shall
McGraw-Hill and/or its licensors be liable for any indirect, incidental, special, punitive, consequential or similar
damages that result from the use of or inability to use the work, even if any of them has been advised of the possibility of such damages. This limitation of liability shall apply to any claim or cause whatsoever whether such claim
or cause arises in contract, tort or otherwise.
DOI: 10.1036/0071418148
For more information about this title, click here.
Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Block 1 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Block 2 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Block 3 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Block 4 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Block 5 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Block 6 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Block 7 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Block 8 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Block 1 Answers, Explanations, and References. . . . . 181
Block 2 Answers, Explanations, and References. . . . . 201
Block 3 Answers, Explanations, and References. . . . . 219
Block 4 Answers, Explanations, and References. . . . . 237
Block 5 Answers, Explanations, and References. . . . . 253
Block 6 Answers, Explanations, and References. . . . . 271
Block 7 Answers, Explanations, and References. . . . . 291
Block 8 Answers, Explanations, and References. . . . . 311
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
v
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
Preface
The current format of the United States Medical Licensing Examination
(USMLE) Step 1 emphasizes clinical vignettes as the primary test questions. The examination is 400 questions, broken into eight blocks of 50
questions each. Examinees have one hour to complete each block.
Clinical Vignettes for the USMLE Step 1: Second Edition parallels this format. The book contains 400 clinical-vignette-style questions covering the
basic sciences and assembled based on the published content outline for
the USMLE Step 1. The questions are divided into eight blocks of 50 questions. As on the Step 1 exam, each block tests the examinee in all basic science areas. Halfway through each block, a stopwatch set at 30 minutes is
included to remind the examinee of the one-hour limit. Answers are in the
second half of the book. Each answer is accompanied by a concise but
comprehensive explanation and is referenced to a key textbook and/or
journal article for further reading.
The questions in this book were culled from the nine PreTest® Basic
Science books. The publisher acknowledges and thanks the following
authors for their contributions to this book:
Anatomy, Histology, & Cell Biology: Robert Klein, Ph.D. and
James C. McKenzie, Ph.D.
Behavioral Sciences: Michael H. Ebert, M.D.
Biochemistry & Genetics: Golder Wilson, M.D.
Microbiology: Richard C. Tilton, Ph.D.
Neuroscience: Alan Siegel, Ph.D. and Heidi Siegel, M.D.
Pathology: Earl Brown, M.D.
Pathophysiology: Maurice Mufson, M.D.
Pharmacology: Arnold Stern, M.D., Ph.D.
Physiology: James C. Ryan, Ph.D. and Michael Wang, Ph.D.
McGraw-Hill
August 2001
vii
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
PRE
TEST
®
Clinical Vignettes
for the USMLE Step 1
PreTest® Self-Assessment and Review
This page intentionally left blank.
BLOCK 1
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
BLOCK 1
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Questions
1-1. A 6-year-old boy has received a deep puncture wound while playing
in his neighbor’s yard. His records indicate that he has had the standard
DPT immunizations and a booster when he entered school. What is the
most appropriate therapy for this child?
a.
b.
c.
d.
e.
Tetanus toxoid
Tetanus antitoxin
Both toxoid and antitoxin at the same site
Toxoid and antitoxin at different sites
No treatment
1-2. A 67-year-old male presents with a slowly growing lesion that
involves the lower portion of his left lower eyelid. You examine the lesion
and find it to be a pearly papule with raised margins and a central ulcer
(rodent ulcer). Histologic sections from this lesion would most likely reveal
a.
b.
c.
d.
e.
Reactive epidermal cells surrounding a central superficial ulcer
Infiltrating groups of basaloid cells with peritumoral clefting
Infiltrating groups of eosinophilic cells with keratin formation
Dermal aggregates of small cells histologically similar to oat cell carcinoma
An in situ lesion with full-thickness epidermal atypia
3
4
Clinical Vignettes for the USMLE Step 1
1-3. Calcification of the internal carotid artery, which impinges upon the
lateral half of the right optic nerve prior to its entrance to the brain of a 68year-old woman, results in certain visual deficits. The most likely visual
deficits will be
a.
b.
c.
d.
e.
Total blindness of the right eye
Right nasal hemianopsia
Right homonymous hemianopsia
Right bitemporal hemianopsia
Right upper homonymous quadrantanopia
1-4. An HIV-positive patient asks if you can tell him the chances of him
progressing to symptomatic AIDS. Which one of the following tests would
be most useful?
a.
b.
c.
d.
e.
CD4 lymphocyte count
HIV antibody test
HIV RT PCR
Neopterin
HIV p24 antigen
1-5. An adult patient presents with the sudden onset of massive diarrhea.
Grossly, this individual’s stool has the appearance of “rice-water” because of
the presence of flecks of mucus. Cultures of this patient’s stool grow Vibrio
cholerae, a curved, gram-negative rod that secretes an enterotoxin consisting of a toxic A subunit and a binding B subunit. The cholera enterotoxin
causes massive diarrhea by
a.
b.
c.
d.
e.
Inhibiting the conversion of Gi-GDP to Gi-GTP
Inhibiting the conversion of Gs-GTP to Gs-GDP
Stimulating the conversion of Gi-GDP to Gi-GTP
Stimulating the conversion of Gs-GDP to Gs-GTP
Stimulating the conversion of Gs-GTP to Gs-GDP
1-6. A 26-year-old female with acquired immunodeficiency syndrome
(AIDS) develops cryptococcal meningitis. She refuses all intravenous medication. Which antifungal agent can be given orally to treat the meningeal
infection?
a.
b.
c.
d.
Ketoconazole
Amphotericin B
Fluconazole
Nystatin
Block 1
Questions
5
1-7. Methicillin-resistant S. aureus (MRSA) was isolated from 7 patients in
a 14-bed intensive care unit. All patients were isolated and the unit closed
to any more admissions. Which one of the following reasons best explains
these rigorous methods to control MRSA?
a. MRSA is inherently more virulent than other staphylococci
b. The alternative for treatment of MRSA is vancomycin, an expensive and potentially toxic antibiotic
c. MRSA causes toxic shock syndrome
d. MRSA spreads more rapidly from patient to patient than antibiotic-susceptible
staphylococci do
e. MRSA is resistant to penicillin
Questions 1-8 through 1-10
A 43-year-old male is recovering from an infectious disease and experiences a marked instability in his blood pressure with episodes of spiking
of blood pressure. After a series of extensive examinations, it was concluded that this disorder was due to the effects of the infectious agent upon
a component of the peripheral nervous system.
1-8. Logical sites where an infectious agent could produce such an effect
include the
a.
b.
c.
d.
e.
Superior ganglia of cranial nerves IX and X
Geniculate and trigeminal ganglia
Otic and superior salivatory ganglia
Carotid sinus and aortic arch
Carotid and aortic bodies
1-9. The (appropriate) receptors situated in the sites listed in question 1-8
respond best to:
a.
b.
c.
d.
e.
Stretch
Change in chloride ion concentration
Contractions of the gut
Decrease in oxygen concentration
Increase in carbon dioxide concentration
6
Clinical Vignettes for the USMLE Step 1
1-10. Neurons situated in the (appropriate) sites indicated in question 1-8
mediate their effects by projecting directly to the:
a.
b.
c.
d.
e.
Trigeminal spinal nucleus
Fastigial nucleus
Midbrain reticular formation
Solitary nucleus
Autonomic nuclei of the facial nucleus (cranial nerve VII)
1-11. A four-day-old male infant weighing 7 lb, 6 oz is brought to the
emergency room by his parents. The examining emergency room physician
notes that his skin and sclerae are icteric. A blood test indicates elevated
unconjugated bilirubin in the serum. The elevated bilirubin levels in this
patient are most likely the result of
a.
b.
c.
d.
e.
Deficiency of enzymes regulating bilirubin solubility
Hepatocellular proliferation
Decreased destruction of red blood cells
Dilation of the common bile duct
Increased hepatocyte uptake of bilirubin
1-12. A 39-year-old male with aortic insufficiency and a history of no drug
allergies is given an intravenous dose of antibiotic as a prophylaxis preceding the insertion of a valve prosthesis. As the antibiotic is being infused, the
patient becomes flushed over most of his body. What antibiotic was given?
a.
b.
c.
d.
e.
Vancomycin
Gentamicin
Erythromycin
Penicillin G
Tetracycline
1-13. For almost three years, a 50-year-old woman has been caring for her
mother who is chronically ill with Alzheimer’s disease. A recent immunologic assessment of the caregiver daughter found that her
a.
b.
c.
d.
e.
Cellular immune system control of latent viruses was poor
Percentage of T lymphocytes was high
Helper/suppressor ratio was higher than normal
Circulating neutrophils were decreased in number
Natural killer cells were higher in number
Block 1
Questions
7
1-14. An anemic patient has the following red cell indexes: mean corpuscular volume, 70 mm3; mean corpuscular hemoglobin, 22 pg; and mean
corpuscular hemoglobin concentration, 34%. These values are most consistent with a diagnosis of
a.
b.
c.
d.
e.
Folic acid–deficiency anemia
Iron-deficiency anemia
Pernicious anemia
Sideroblastic anemia
Thalassemia minor
1-15. A 26-year-old female with reactive depression complains of missing
her period and having milk discharge from her breasts. She has no signs of
pregnancy, including a negative pregnancy test. Which of the following
might have caused these findings?
a.
b.
c.
d.
e.
Clomipramine
Amoxapine
Fluoxetine
Mirtazapine
Tranylcypromine
1-16. A young skier with normal pulmonary function (minute volume 4
L; pulmonary blood flow 5 L/min) who is recovering from a tibial fracture
suddenly develops right-sided chest pain and tachypnea. Embolic occlusion of the right pulmonary artery is suspected. Which of the following
alveolar gas measurements would immediately confirm the diagnosis?
a.
b.
c.
d.
e.
PO2 (mmHg)
125
125
100
80
80
PCO2 (mmHg)
60
20
40
20
60
1-17. A 22-year-old female carrying a preterm pregnancy (33 weeks) is in
labor. Which of the following drugs can be given to the mother to promote
fetal lung maturity?
a.
b.
c.
d.
e.
Betamethasone
Fludrocortisone
Metyrapone
Spironolactone
Triamcinolone
8
Clinical Vignettes for the USMLE Step 1
1-18. This HIV-positive patient with a viral load of 750,000 copies of HIV
RNA/ml and a total CD4 count of 50 is at an increased risk for a number of
infectious diseases. For which of the following diseases is the patient at no
more added risk than an immunocompetent host?
a.
b.
c.
d.
e.
Pneumocystic pneumonia
Mycobacterial disease
Kaposi’s sarcoma
Pneumococcal pneumonia
Herpes simplex virus
1-19. A 20-year-old male with herpes simplex of the lips is treated with
famciclovir. What is the mechanism of action of famciclovir?
a.
b.
c.
d.
e.
Cross-linking of DNA
Strand breakage of DNA
Inhibition of viral DNA synthesis
Inhibition of nucleotide interconversions
Inhibition of a viral kinase
1-20. A child has ingested cyanide from her parents’ garage and is rushed
to the emergency room. Which of the following components of the citric
acid cycle will be depleted first in this child?
a.
b.
c.
d.
e.
NAD+ cofactor
Citrate synthase
Aconitase
Citrate production
Acetyl coenzyme A (CoA) production
1-21. Analysis of a patient’s stool reveals small structures resembling rice
grains; microscopic examination shows these to be proglottids. The most
likely organism in this patient’s stool is
a.
b.
c.
d.
e.
Enterobius vermicularis
Ascaris lumbricoides
Necator americanus
T. saginata
Trichuris trichiura
Block 1
Questions
9
1-22. A Nigerian medical student studying in the United States develops
hemolytic anemia after taking the oxidizing antimalarial drug pamaquine.
This severe reaction is most likely due to
a.
b.
c.
d.
e.
Glucose-6-phosphate dehydrogenase deficiency
Concomitant scurvy
Vitamin C deficiency
Diabetes
Glycogen phosphorylase deficiency
1-23. A person ascends to the top of a mountain where the atmospheric
pressure is below normal. Which one of the following blood gases was
drawn from the person at the top of the mountain?
a.
b.
c.
d.
e.
PO2
PCO2
50
60
80
100
120
30
40
50
40
30
10
Clinical Vignettes for the USMLE Step 1
1-24. A 2-week-old baby is hospitalized for inadequate feeding and poor
growth. The parents are concerned by the child’s weak cry. An experienced
grandmother accompanies them, saying she thought the cry sounded like
a cat’s meow. The grandmother also states that the baby doesn’t look much
like either parent. The physician orders a karyotype after noting a small
head size (microcephaly) and subtle abnormalities of the face. Which of the
results pictured below is most likely?
a.
b.
c.
d.
e.
Result A
Result B
Result C
Result D
Result E
A
Block 1
B
C
Questions
11
12
D
E
Clinical Vignettes for the USMLE Step 1
Block 1
Questions
13
1-25. A 34-year-old female presents with recurrent episodes of severe
headaches, palpitations, tachycardia, and sweating. A physical examination
reveals her blood pressure to be within normal limits; however, during one
of these episodes of headaches, palpitations, and tachycardia, her blood
pressure is found to be markedly elevated. Workup finds a small tumor of
the right adrenal gland. Which one of the following is most likely to be
increased in the urine of this individual?
a.
b.
c.
d.
e.
Acetone
Aminolevulinic acid (ALA)
Hydroxy-indoleacetic acid (HIAA)
N-formiminoglutamate (FIGlu)
Vanillylmandelic acid (VMA)
14
Clinical Vignettes for the USMLE Step 1
YOU SHOULD HAVE COMPLETED APPROXIMATELY
25 QUESTIONS AND HAVE 30 MINUTES REMAINING.
1-26. A patient presents to the physician’s office to ask questions about
color blindness. The patient is color-blind, as is one of his brothers. His
maternal grandfather was color-blind, but his mother, father, daughter, and
another brother are not. His daughter is now pregnant. The risk that her
child will be color-blind is
a.
b.
c.
d.
e.
100%
50%
25%
12.5%
Virtually 0
1-27. A 55-year-old female given a general anesthetic for a surgical procedure develops hyperthermia, hypertension, hyperkalemia, tachycardia,
muscle rigidity, and metabolic acidosis. Which of the following general
anesthetics did she receive?
a.
b.
c.
d.
e.
Ketamine
Midazolam
Thiopental
Propofol
Halothane
Block 1
Questions
15
1-28. A 30-year-old female stored her contact lenses in tap water. She
noticed deterioration of vision and visited an ophthalmologist who diagnosed her with severe retinitis. Culture of the water as well as vitreous fluid
would most likely reveal
a.
b.
c.
d.
e.
Naegleria
Pneumocystis
Acanthamoeba
Babesia
Entamoeba coli
1-29. A 25-year-old male reports to his physician that he has not been able
to sleep for over two days and has been having “strange reactions.” These
reactions are most apt to be caused by
a.
b.
c.
d.
e.
Increased levels of blood cortisol
Physiologic stress in response to sleep deprivation
The effects of the rebound phenomenon
Perceptual distortions
Feelings of excessive tiredness
1-30. A 45-year-old male is hospitalized for treatment of myocardial
infarction. His father and a paternal uncle also had heart attacks at an early
age. His cholesterol is elevated, and lipoprotein electrophoresis demonstrates an abnormally high ratio of low- to high-density lipoproteins (LDL
to HDL). Which of the following is the most likely explanation for this
problem?
a.
b.
c.
d.
e.
Mutant HDL is not responding to high cholesterol levels
Mutant LDL is not responding to high cholesterol levels
Mutant caveolae proteins are not responding to high cholesterol levels
Mutant LDL receptors are deficient in cholesterol uptake
Intracellular cholesterol is increasing the number of LDL receptors
1-31. A 3-year-old child presents at the physician’s office with symptoms
of coryza, conjunctivitis, low-grade fever, and Koplik’s spots. The causative
agent of this disease belongs to which group of viruses?
a.
b.
c.
d.
e.
Adenovirus
Herpesvirus
Picornavirus
Orthomyxovirus
Paramyxovirus
16
Clinical Vignettes for the USMLE Step 1
1-32. A 25-year-old female suspected of having vitamin D–resistant rickets has decreased blood phosphate levels. Aside from high-dose vitamin D
and oral phosphate, an alternative therapeutic approach might be the use
of which of the following?
a.
b.
c.
d.
e.
Estrogen
Pamidronate
Hydrochlorothiazide
Prednisone
Calcitrol
1-33. A 52-year-old female presents with nausea, fatigue, muscle weakness, and intermittent pain in her left flank. Laboratory examination
reveals an increased serum calcium and a decreased serum phosphorus.
The patient’s plasma parathyroid hormone levels are increased, but
parathyroid hormone–related peptide levels are within normal limits. Urinary calcium is increased, and microhematuria is present. The patient’s
abnormality is most likely caused by
a.
b.
c.
d.
e.
Primary hyperparathyroidism
Primary hypoparathyroidism
Pseudohypoparathyroidism
Secondary hyperparathyroidism
Secondary hypoparathyroidism
Block 1
Questions
17
1-34. The accompanying x-ray shows the shoulder of an 11-year-old
female who fell off the monkey bars, extending her arm in an attempt to
break her fall. The small arrows indicate a fracture in the area of the surgical neck of the humerus. The large arrows indicate
a.
b.
c.
d.
e.
A fracture at the anatomic neck of the humerus
The glenohumeral joint
The joint space between the proximal humerus and the acromion of the scapula
The proximal humeral epiphyseal plate
What is commonly called a shoulder separation
18
Clinical Vignettes for the USMLE Step 1
1-35. A newborn begins vomiting after feeding, becomes severely jaundiced, and has liver disease. Treatment for possible sepsis is initiated, and
the urine is found to have reducing substances. A blood screen for galactosemia is positive, and lactose-containing substances are removed from
the diet. Lactose is toxic in this case because
a.
b.
c.
d.
e.
Excess glucose accumulates in the blood
Galactose is converted to the toxic substance galactitol (dulcitol)
Galactose competes for glucose during hepatic glycogen synthesis
Galactose is itself toxic in even small amounts
Glucose metabolism is shut down by excess galactose
1-36. A 36-year-old male with a bipolar disorder is treated with lithium.
Among the following adverse effects, which is associated with lithium treatment?
a.
b.
c.
d.
e.
Browning of the vision
Hypothyroidism
Agranulocytosis
Neuroleptic malignant syndrome
Pseudodepression
1-37. A 24-year-old female presents with severe pain during menses (dysmenorrhea). To treat her symptoms, you advise her to take indomethacin in
the hopes that it will reduce her pain by interfering with the production of
a.
b.
c.
d.
e.
Bradykinin
Histamine
Leukotrienes
Phospholipase A2
Prostaglandin F2
Block 1
Questions
19
1-38. A pathologist views the following tissues (A and B) in a biopsy. She
determines that the tissues are normal. The presence of both of these tissues indicates that the sample was taken from the region of the junction
between the
a.
b.
c.
d.
e.
Anal canal and rectum
Esophagus and stomach
Skin of the face and mucous epithelium of the lip
Stomach and duodenum
Vagina and cervix
20
Clinical Vignettes for the USMLE Step 1
1-39. A child develops chronic diarrhea and liver inflammation in early
infancy when the mother begins using formula that includes corn syrup.
Evaluation of the child demonstrates sensitivity to fructose in the diet.
Which of the following glycosides contains fructose and therefore should
be avoided when feeding or treating this infant?
a.
b.
c.
d.
e.
Sucrose
Oaubain
Lactose
Maltose
Streptomycin
1-40. A 49-year-old man who smokes two packs of cigarettes a day presents
with a lung mass on x-ray and recent weight gain. Laboratory examination
shows hyponatremia with hyperosmolar urine. The patient probably has
a.
b.
c.
d.
e.
Renal failure
Pituitary failure
Conn’s syndrome
Cardiac failure
Inappropriate ADH
1-41. A college student takes part in a sleep laboratory experiment in
which he is awakened repeatedly when his electroencephalogram (EEG)
indicates that he has entered rapid-eye-movement (REM) sleep. This disruption of normal sleep is most likely to produce
a.
b.
c.
d.
e.
A rebound phenomenon of increased dreaming
An increase in anxiety and irritability
Acceleration of memory formation of emotionally toned words
A decrement in intellectual function
A temporary increase in nightmares
1-42. A 33-year-old female patient treated with haloperidol for a history of
schizophrenia is seen in the ED because of complaints of fever, stiffness,
and tremor. Her temperature is 104°F, and her serum creatine kinase (CK)
level is elevated. What has occurred?
a.
b.
c.
d.
e.
Overdose
Allergy
Neuroleptic malignant syndrome (NMS)
Tardive Dyskinesia
Parkinsonism
Block 1
Questions
21
1-43. A teenage girl presents in the emergency room with paroxysms of
dyspnea, cough, and wheezing. Her parents indicate that she has had
these “attacks” during the past winter, and that they have worsened and
become more frequent during the spring allergy season. Which of the following cell types is correctly matched to a function it may perform in this
patient’s disease?
a.
b.
c.
d.
e.
Alveolar macrophages, enhanced mucociliary transport
Plasma cells, bronchoconstriction
Eosinophils, bronchodilation
Goblet cells, hyposecretion
Mast cells, edema
1-44. A young man with hypercholesterolemia is rushed to the hospital
with crushing chest pain radiating to his left arm and a probable heart
attack. Which of the following treatments should be considered?
a.
b.
c.
d.
e.
A platelet transfusion
Heparin infusion
Thrombin infusion
Fibrinogen infusion
Tissue plasminogen activator infusion
1-45. A patient becomes markedly tetanic following a recent thyroidectomy. This symptom can be rapidly reversed by the administration of
a.
b.
c.
d.
e.
Vitamin D
Calcitonin
PTH
Plicamycin (mithramycin)
Calcium gluconate (CaG)
1-46. A 26-year-old woman has been amenorrheic for 2.5 months. Your
first choice for diagnostic evaluation is
a.
b.
c.
d.
e.
hCG
LH
Estradiol
Prolactin
Progesterone
22
Clinical Vignettes for the USMLE Step 1
1-47. A 45-year-old man was riding a snowmobile and hit a snow-covered
rocky outcropping. While recovering from the accident, he slipped and fell
on the outcropping and now is experiencing pain in the gluteal region. In
this CT scan, the dark linear structure indicated by the arrow is
a.
b.
c.
d.
e.
A fracture of the ilium
The sacroiliac joint
A spinal nerve
The superior gluteal artery
The inferior gluteal artery
Block 1
Questions
23
1-48. A 36-year-old male heroin addict is seen in the ED because he cannot be aroused from sleep. On examination, he has shallow breathing and
pinpoint pupils. Naloxone is administered, and the patient wakes up.
Which of the opiate receptor subtypes that binds naloxone is responsible
for reversing the respiratory depression and miosis?
a. δ
b. κ
c. µ
1-49. A 49-year-old female presents with signs of anemia and states that
every morning her urine is dark. Workup reveals that her red blood cells
lyse in vitro with acid (positive Ham’s test). What is the best diagnosis for
this patient?
a.
b.
c.
d.
e.
Warm autoimmune hemolytic anemia
Paroxysmal nocturnal hemoglobinuria
Paroxysmal cold hemoglobinuria
Isoimmune hemolytic anemia
Cold-agglutinin autoimmune hemolytic anemia
1-50. A 34-year-old man has been diagnosed with chronic paranoid schizophrenia for 10 years. He is currently in a psychiatric hospital and is not on
psychotropic medications. More than 50% of individuals with this diagnosis and off medications would have abnormalities in which of these tests?
a.
b.
c.
d.
e.
Lactate infusion test
Dexamethasone suppression test
Eye pursuit test
Thyrotropic releasing hormone (TRH) stimulation test
Prolactin stimulation test
This page intentionally left blank.
BLOCK 2
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
BLOCK 2
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Questions
2-1. A patient with reduced VC, FRC, and RV is found to have a normal
pH. A tentative diagnosis of diffuse interstitial fibrosis is made. Which of
the following characteristics are consistent with this disease?
a.
b.
c.
d.
e.
An increase in lung compliance
A decrease in respiratory rate
An increase in the V/Q ratio
A decrease in PaCO2
An increase in the FEV1/FVC ratio
2-2. A 45-year-man has decreased libido and decreased sexual function. A
large pituitary tumor is found. His prolactin is 20 (less than 15). Testing of
his pituitary-gonadal axis most likely will show
a.
b.
c.
d.
e.
Normal testosterone and low LH
High testosterone and normal LH
Low testosterone and low LH
Normal testosterone and normal LH
Low testosterone and high LH
27
28
Clinical Vignettes for the USMLE Step 1
2-3. A 45-year-old male with a history of colonic diverticulosis complains
of fever with pain and swelling in the rectal area. You are concerned that
the colonic diverticulum may have become infected (diverticulitis) and
ruptured into the space indicated by the * in this CT scan. Which of the
following is correct regarding the indicated space?
a.
b.
c.
d.
It is called the paracolic gutter
The space is largely filled with muscle
The space is located superior to the pelvic diaphragm
Pus from the abscessed diverticuli in that space can extend anteriorly to the perineal body, inferior to the urogenital diaphragm
e. Pus from the abscessed diverticuli in that space can extend superiorly anterior
to the sacrum
Block 2
Questions
29
2-4. A jaundiced one-day-old premature infant with an elevated free bilirubin is seen in the premature-baby nursery. The mother received an antibiotic
combination preparation containing sulfamethizole for a urinary tract infection (UTI) one week before delivery. You suspect that the infant’s findings
are caused by the sulfonamide because of the following mechanism:
a.
b.
c.
d.
Enhanced synthesis of bilirubin
Competition between the sulfonamide and bilirubin for binding sites on albumin
Inhibition of bilirubin degradation
Inhibition of urinary excretion of bilirubin
2-5. A 35-year-old woman who underwent a modified radical mastectomy
of her right breast for infiltrating ductal carcinoma 2 years ago presents
with enlargement of her right breast. The breast has a swollen, reddiscolored appearance. It is diffusely indurated and tender on palpation.
Multiple axillary lymph nodes are palpable in the lower axilla. The working clinical diagnosis is inflammatory carcinoma. Microscopic sections
from this red, indurated area are most likely to reveal
a.
b.
c.
d.
e.
Duct ectasia with numerous plasma cells
Extensive invasion of dermal lymphatics
Infiltrating malignant ducts surrounded by numerous neutrophils
Malignant vascular tumor forming slitlike spaces
Marked dermal desmoplasia
2-6. A man drinks 2 L of water to replenish the fluids lost by sweating during a period of exercise. Compared with the situation prior to the period of
sweating,
a.
b.
c.
d.
e.
His intracellular fluid will be hypertonic
His extracellular fluid will be hypertonic
His intracellular fluid volume will be greater
His extracellular fluid volume will be greater
His intracellular and extracellular fluid volumes will be unchanged
30
Clinical Vignettes for the USMLE Step 1
2-7. A 75-year-old male, postprostatectomy for carcinoma of the prostate
with local metastasis found during surgery, would best be treated with
which of the following?
a.
b.
c.
d.
e.
Mifepristone
Spironolactone
Aminoglutethimide
Leuprolide
Fludrocortisone
2-8. A nurse develops clinical symptoms consistent with hepatitis. She
recalls sticking herself with a needle approximately 4 months before after
drawing blood from a patient. Serologic tests for HBsAg, antibodies to
HBsAg, and hepatitis A virus (HAV) are all negative; however, she is positive for IgM core antibody. The nurse
a.
b.
c.
d.
Does not have hepatitis B
Has hepatitis A
Is in the late stages of hepatitis B infection
Is in the “window” (after the disappearance of HBsAg and before the appearance of anti-HBsAg)
e. Has hepatitis C
2-9. A 22-year-old male with a five-year history of bronchial asthma has
developed increased frequency and severity of acute asthmatic attacks. A
low dose of which inhaled steroid could be added to his treatment regimen?
a.
b.
c.
d.
e.
Prednisolone
Amcinonide
Beclomethasone
Cortisone
Fluocinolone
2-10. A patient has muscular weakness. His parents and sister do not have
weakness, but his mother’s brother has weakness. You suspect Duchenne’s
muscular dystrophy. This is an example of
a.
b.
c.
d.
Autosomal recessive inheritance
X-linked recessive inheritance
Semidominant inheritance
Autosomal dominant inheritance
Block 2
Questions
31
2-11. An elderly patient who becomes acutely short of breath presents
with the combination of hypotension, elevated jugular venous pressure,
and muffled heart sounds. This triad of symptoms is most suggestive of
a.
b.
c.
d.
e.
Chronic pericarditis
Chronic pericardial effusion
Cardiac tamponade
Dissecting aortic aneurysm
Right heart failure
2-12. A patient presents with keratoconjunctivitis. The differential diagnosis should include infection with which of the following viruses?
a.
b.
c.
d.
e.
Parvovirus
Adenovirus
Epstein-Barr virus
Respiratory syncytial virus
Varicella-zoster virus
2-13. A 2-year-old infant is brought to the emergency room with
hemolytic uremic syndrome and thrombocytopenia. Which one of the following bacteria would most likely be isolated from a stool specimen?
a.
b.
c.
d.
e.
Shigella
Salmonella
Aeromonas
E. coli 0157/H7
Enterobacter
2-14. Following surgery involving the lateral wall of the pelvis, a patient
reported anesthesia over the medial thigh. Subsequent examination
revealed weakened adduction of the thigh. Which nerve was most likely
injured during the pelvic surgery?
a.
b.
c.
d.
e.
Pudendal nerve
Genitofemoral nerve
Superior gluteal nerve
Femoral nerve
Obturator nerve
32
Clinical Vignettes for the USMLE Step 1
2-15. You have been asked to consult regarding stress in the workplace in
a busy factory. One group of workers have jobs that are self-paced. A second
group have jobs that are machine-paced and therefore largely out of the
workers’ control. The workers who do not control their pace of work would
be differentiated from the other group in physiologic response by a much
greater release of
a.
b.
c.
d.
e.
Catecholamines
Thyroid hormone
Serotonin
Prostaglandins
γ-Aminobutyric acid (GABA)
2-16. An AIDS patient complains of headaches and disorientation. A clinical diagnosis of Toxoplasma encephalitis is made and Toxoplasma cysts were
observed in a brain section (see figure below). Which one of the following
antibody results would be most likely in this patient?
a.
b.
c.
d.
e.
IgM nonreactive, IgG nonreactive
IgM nonreactive, IgG reactive (low titer)
IgM reactive (low titer), IgG reactive (high titer)
IgM reactive (high titer), IgG reactive (high titer)
IgM reactive (high titer), IgG nonreactive
Block 2
Questions
33
2-17. A 72-year-old woman with emphysema presents to the emergency
room with fatigue and respiratory distress. Which set of arterial blood gas
values below would represent her condition and reflect a shift of the hemoglobin oxygen dissociation curve to the right?
a.
b.
c.
d.
e.
pH 7.05, bicarbonate 15 mM, PCO2 60, PO2 88
pH 7.15, bicarbonate 10 mM, PCO2 30, PO2 88
pH 7.25, bicarbonate 15 mM, PCO2 30, PO2 88
pH 7.40, bicarbonate 24 mM, PCO2 60, PO2 88
pH 7.45, bicarbonate 15 mM, PCO2 60, PO2 88
2-18. At the time of autopsy of a 39-year-old female who died of complications of systemic lupus erythematosus, several medium-sized vegetations
are found on both sides of the mitral valve and tricuspid valve. These cardiac vegetations are most likely the result of
a.
b.
c.
d.
e.
Turbulent blood flow through an incompetent mitral valve
Abnormal secretion of a vasoactive amine
Presence of an anticardiolipin antibody
Cachexia produced by a hypercoagulable state
Bacterial colonization of an abnormal valve
2-19. A 25-year-old male is seen in the emergency department (ED). He is
disoriented but states that he has had nausea, vomiting, abdominal pain,
and diarrhea since he took “too many pain pills.” Before he can tell you
more, he loses consciousness. Liver function tests are abnormal. In addition to gastric lavage, what is the appropriate treatment?
a.
b.
c.
d.
e.
Naloxone
Diphenoxylate
N-acetyl-L-cysteine
Prochlorperazine
Pralidoxime
34
Clinical Vignettes for the USMLE Step 1
2-20. A comatose laboratory technician is rushed into the emergency
room. She dies while you are examining her. Her most dramatic symptom
is that her body is literally hot to your touch, indicating an extremely high
fever. You learn that her lab has been working on metabolic inhibitors and
that there is a high likelihood that she accidentally ingested one. Which
one of the following is the most likely culprit?
a.
b.
c.
d.
e.
Barbiturates
Piericidin A
Dimercaprol
Dinitrophenol
Cyanide
2-21. A 52-year-old male patient, who has smoked two packs of cigarettes
per day for the past 38 years, presents with diminished breath sounds
detected by auscultation accompanied by faint high-pitched rhonchi at the
end of each expiration and a hyperresonant percussion note. In addition,
he shows discomfort during breathing and is using extra effort to involve
accessory muscles to lift the sternum. The diminished lung sounds in this
patient are primarily due to which cellular events?
a. Monocytic infiltration leading to collagenase destruction of bronchiolar connective tissue support
b. Neutrophilic infiltration leading to destruction of bronchiolar and septal elastic
fibers
c. Monocytic infiltration leading to breakdown of the bronchiolar smooth muscle
d. Neutrophilic infiltration leading to excess production of antiprotease activity in
the lung parenchyma
e. Monocytic infiltration leading to excess production of antiprotease activity in
the lung parenchyma
2-22. Parents of a child with attention deficit hyperactivity disorder
(ADHD) consult with you to inquire about the heritability of the disorder.
The husband had attention span and learning problems in secondary
school. One of his brothers did also, and an uncle may have had learning
problems. You response would include the fact that ADHD has a heritability of approximately
a.
b.
c.
d.
e.
70%
60%
50%
40%
30%
Block 2
Questions
35
2-23. A 4-year-old male with mental retardation, self-mutilation, and
hyperuricemia is likely to have a deficiency of an enzyme involved in the
a.
b.
c.
d.
e.
Conversion of homogentisic acid to methylacetoacetate
Degradation of galactocerebroside
Breakdown of branched-chain amino acids
Recycling of guanine and hypoxanthine
Synthesis of UMP and CTP
2-24. A teenage girl is brought to the medical center because of her complaints that she gets too tired when asked to participate in gym class. A
consulting neurologist finds muscle weakness in the girl’s arms and legs.
When no obvious diagnosis can be made, biopsies of her muscles are taken
for tests. Chemistries reveal greatly elevated amounts of triacylglycerides
esterified with primarily long-chain fatty acids. Pathology reports the presence of significant numbers of lipid vacuoles in the muscle biopsy. Which
one of the following is the most likely diagnosis?
a.
b.
c.
d.
e.
Fatty acid synthase deficiency
Tay-Sachs disease
Carnitine deficiency
Biotin deficiency
Lipoprotein lipase deficiency
2-25. A person who had recently consumed half a box of raspberries came
down with severe watery diarrhea. Surprisingly, the patient felt tired for a
few days and had a low-grade fever. The most likely cause of infection is
a.
b.
c.
d.
e.
Cryptosporidium
Escherichia coli 0157:H7
Isospora
Vibrio
Cyclospora
36
Clinical Vignettes for the USMLE Step 1
YOU SHOULD HAVE COMPLETED APPROXIMATELY
25 QUESTIONS AND HAVE 30 MINUTES REMAINING.
2-26. A 50-year-old male is seen in the emergency department (ED)
with a blood pressure of 260/160 mmHg. Blurring optic discs with indistinct margins are seen on ophthalmologic examination. An intravenous
drip of sodium nitroprusside is administered. What is the mechanism of
action of sodium nitroprusside?
a.
b.
c.
d.
e.
f.
g.
h.
i.
α-adrenergic receptor agonist
α-adrenergic receptor antagonist
β-adrenergic receptor agonist
β-adrenergic receptor antagonist
Ganglionic blocking agent
Depletion of nerve terminal storage of NE
Direct smooth-muscle vasodilator
ACE antagonist
Angiotensin receptor antagonist
Block 2
Questions
37
2-27. A 19-year-old male presents with a rash that involves a large, irregular portion of his trunk. Examination reveals several annular lesions that
have a raised papulovesicular border with central hypopigmentation.
Examination of this area under a Wood’s lamp reveals a yellow fluorescence. A scraping of this area viewed under the microscope after KOH is
added reveals characteristic “spaghetti and meatball” forms. What is the
cause of this skin lesion?
a.
b.
c.
d.
e.
Malassezia furfur
Molluscum contagiosum
Sarcoptes scabiei
Staphylococcus aureus
Trichophyton rubrum
2-28. A child with a large head, multiple fractures, and blue scleras
(whites of the eyes) is evaluated for osteogenesis imperfecta (166200). One
study involves labeling of collagen chains in tissue culture to assess their
mobility by gel electrophoresis. Amino acids labeled with radioactive carbon 14 are added to the culture dishes in order to label the collagen. Which
of the following amino acids would not result in labeled collagen?
a.
b.
c.
d.
e.
Serine
Glycine
Aspartate
Glutamate
Hydroxylserine
2-29. A physician examines a patient who complains of pain and paresthesia in the left leg. The distribution of the pain—running down the
medial aspect of the leg and the medial side of the foot and including the
great toe—is suggestive of a herniated intervertebral disk. The physician
links the distribution of symptoms with nerve L4 and concludes that herniation has occurred at which location?
a.
b.
c.
d.
e.
L3–L4 intervertebral disk
L4–L5 intervertebral disk
L5–S1 intervertebral disk
S1–S2 intervertebral disk
Insufficient data to determine
38
Clinical Vignettes for the USMLE Step 1
2-30. A former heroin addict is maintained on methadone, but succumbs
to temptation and buys an opioid on the street. He takes it and rapidly goes
into withdrawal. Which opioid did he take?
a.
b.
c.
d.
e.
Meperidine
Heroin
Pentazocine
Codeine
Propoxyphene
2-31. A 26-year-old female acutely develops lower abdominal pain and
vaginal bleeding. While in the bathroom she passes a cast of tissue composed of clot material and then collapses. She is brought to the hospital,
where a physical examination reveals a soft, tender mass in right adnexa
and pouch of Douglas. Histologic examination of the tissue passed in the
bathroom reveals blood clots and decidualized tissue. No chorionic villi or
trophoblastic tissue are present. Which one of the following conditions is
most likely present in this individual?
a.
b.
c.
d.
e.
Aborted intrauterine pregnancy
Complete hydatidiform mole
Ectopic pregnancy
Endometrial hyperplasia
Partial hydatidiform mole
2-32. A young woman had an initial episode of psychosis at age 19, with
paranoid delusions, auditory hallucinations, and disorganized behavior.
She responded well to an atypical neuroleptic, but has not been able to live
independently and develop an occupation. She has had two subsequent
psychotic episodes similar to the initial one. The etiology of her chronic
psychiatric illness is most strongly related to
a.
b.
c.
d.
e.
Environmental factors
Polygenic inheritance
A chromosomal abnormality
Simple recessive inheritance
An inborn error of metabolism
Block 2
Questions
39
2-33. Following childbirth, a woman experienced urinary incontinence,
particularly when coughing. This was most likely caused by tearing of the
a.
b.
c.
d.
e.
Puborectalis muscle
Obturator internus muscle
Pubococcygeus muscle
Superficial transverse perineus muscle
Piriformis muscle
2-34. A 22-year-old man comes to the emergency room of your hospital
because he has a diffuse, erythematous rash involving nearly all of his body.
His total WBC count is greater than 100,000 cells/mm3. He also complains
of bone pain, severe irritability, weakness, fatigue, nausea and vomiting,
constipation, photophobia, and polyuria. His electrocardiogram (ECG)
shows shortening of the QT interval, prolongation of the PR interval, and
nonspecific T wave changes. The most likely cause of his symptoms is
a.
b.
c.
d.
Hypercalcemia
Hypocalcemia
Hypophosphatemia
Hyperkalemia
40
Clinical Vignettes for the USMLE Step 1
2-35. An adolescent presents with shortness of breath during exercise and
is found to be anemic. A hemoglobin electrophoresis is performed that is
depicted in the figure below. The adolescent’s sample is run with controls
including normal, sickle trait, and sickle cell anemia, and serum. The adolescent is determined to have an unknown hemoglobinopathy. Which one
of the lanes contains the adolescent’s sample?
a.
b.
c.
d.
e.
Lane A
Lane B
Lane C
Lane D
Lane E
2-36. A 30-year-old pregnant female develops a UTI that is caused by
Chlamydia trachomatis. Of the following, which is the best agent to use in
this patient?
a.
b.
c.
d.
e.
Tetracycline
Levofloxacin
Gentamycin
Erythromycin
Sulfamethoxazole-trimethoprim
Block 2
Questions
41
2-37. A patient takes excessive amounts of bicarbonates to treat his heartburn. Which one of the following blood-gas values will be observed in this
patient?
a.
b.
c.
d.
e.
PaCO2
(mM)
25
35
45
55
65
pH
7.7
7.6
7.5
7.4
7.3
2-38. A 25-year-old female presents with lower abdominal pain, fever,
and a vaginal discharge. Pelvic examination reveals bilateral adnexal (ovarian) tenderness and pain when the cervix is manipulated. Cultures taken
from the vaginal discharge grow Neisseria gonorrhoeae. What is your diagnosis of the cause of this patient’s adnexal pain?
a.
b.
c.
d.
e.
Adenomatoid tumor
Ectopic pregnancy
Endometriosis
Luteoma of pregnancy
Pelvic inflammatory disease
2-39. A newborn female has a large and distorted cranium, short and
deformed limbs, and very blue scleras (whites of the eyes). Radiographs
demonstrate multiple limb fractures and suggest a diagnosis of osteogenesis imperfecta (brittle bone disease). Analysis of type I collagen protein, a
triple helix formed from two α1 and one α2 collagen chains, shows a 50%
reduction in the amount of type I collagen in the baby’s skin. DNA analysis
demonstrates the presence of two normal α1 alleles and one normal α2
allele. These results are best explained by
Deficiency of α1 collagen peptide synthesis
Inability of α1 chains to incorporate into triple helix
Defective α1 chains that interrupt triple helix formation
Incorporation of defective α2 chains that cause instability and degradation of
the triple helix
e. A missense mutation that alters the synthesis of α1 chains
a.
b.
c.
d.
42
Clinical Vignettes for the USMLE Step 1
2-40. A child has mononucleosis-like symptoms yet the test for mononucleosis and the EBV titers are negative. One of the causes of heterophilenegative mononucleosis is
a.
b.
c.
d.
e.
Cytomegalovirus
Herpes simplex virus
Varicella-zoster virus
Adenovirus
Coxsackievirus
2-41. A 43-year-old woman who has suffered from diabetes for 30 years
comes into the clinic. She is anemic with a hematocrit of 22. Which of the
following would most likely explain her condition?
a. Decreased hepatic production of erythropoietin, leading to decreased numbers
of circulating reticulocytes in the bloodstream
b. Increased erythropoietin production by the liver, resulting in increased numbers of reticulocytes
c. Decreased renal erythropoietin production, leading to reduced numbers of red
blood cells
d. Decreased estrogen levels, stimulating hepatic production of erythropoietin
e. Decreased estrogen levels, inhibiting renal production of erythropoietin
2-42. A 15-year-old male attempts suicide with a liquid that causes
intense abdominal pain, skeletal muscle cramps, projectile vomiting,
severe diarrhea, and difficulty swallowing. On examination, he is found to
be volume depleted and is showing signs of alteration of consciousness.
Which of the following may account for these symptoms?
a.
b.
c.
d.
e.
Arsenic (As)
Cadmium (Cd)
Iron (Fe)
Lead (Pb)
Zinc (Zn)
2-43. A patient has arthralgia, a rash, lymphadenopathy, pneumonia but
no fever. Which of the following diseases is most likely based on these
symptoms?
a.
b.
c.
d.
e.
Dengue fever
St. Louis encephalitis
Infectious mononucleosis
Hepatitis
HIV infection
Block 2
Questions
43
2-44. The blood pressure of a 65-year-old male is well controlled by a Ca2+
channel blocker that is used to treat his essential hypertension. When
placed on cimetidine to control symptoms related to gastroesophageal
reflux disease (GERD), he has episodes of dizziness. How does cimetidine’s
effect on Ca2+ channel blockers account for the dizziness?
a.
b.
c.
d.
e.
It increases their rate of intestinal absorption
It decreases their plasma protein binding
It decreases their volume of distribution
It decreases their metabolism by cytochrome P450
It decreases their tubular renal secretion
2-45. An infant smiles every time the parents approach the crib and look
at him. Emotional expressions in an infant, such as smiling, are stereotyped
sequences of movements that are under the control of
a.
b.
c.
d.
e.
A specific sign stimulus
Genetic influences
A conditioned response
Imprinting
Cultural determinants
2-46. A 39-year-old female presents with increasing shortness of breath.
She states that for the past 6 months she has been taking an unauthorized
appetite suppressant to try to lose weight. Physical examination reveals
signs of right heart failure. She is admitted to the hospital to work up her
symptoms, but she dies suddenly. A section from her heart at the time of
autopsy reveals marked thickening of the right ventricle, but the thickness
of the left ventricle is within normal limits. The endocardium does not
appear to be increased in thickness or fibrotic, and the cardiac valves do
not appear abnormal. Neither ventricular cavity is dilated. Which one of
the following best describes this cardiac pathology?
a.
b.
c.
d.
e.
Carcinoid heart disease
Cor pulmonale
Eccentric hypertrophy
Systemic hypertensive heart disease
Volume overload to the heart
44
Clinical Vignettes for the USMLE Step 1
2-47. A 30-year-old man presents with weight gain, dorsocervical fat pad,
and proximal muscle weakness. His urinary free cortisol is significantly elevated and does not suppress with dexamethasone. The plasma ACTH is
undetectable. Your next best diagnostic test is
a.
b.
c.
d.
e.
Serum antidiuretic hormone (ADH)
Chest CT
MRI of the pituitary
ACTH stimulation test
Abdominal CT
Questions 2-48 through 2-49
An elderly female patient complains that she cannot taste the food that
she eats. A careful neurological examination reveals no evidence of peripheral damage of the taste receptors. The evidence suggests, instead, that
there was selective damage of certain regions of the brainstem.
2-48. One of the sites where damage could result in the selective loss of
taste includes the
a.
b.
c.
d.
e.
Superior olivary nucleus
Inferior salivatory nucleus
Solitary nucleus
Spinal nucleus of the trigeminal nerve
Reticular tegmental nucleus of the pons
2-49. A principal target of the brainstem structure (referring to the answer
to the previous question) is the
a.
b.
c.
d.
e.
Anterior thalamic nucleus
Reticular thalamic nucleus
Ventral posteromedial thalamic nucleus
Ventrolateral thalamic nucleus
Dorsomedial thalamic nucleus
Block 2
Questions
45
2-50. A 46-year-old woman presents with a pain in the left leg that worsens on weight-bearing. An x-ray shows demineralization and a decalcified
(EDTA-treated) biopsy shows reduction in bone quantity. The patient had
undergone menopause at age 45 without estrogen replacement. She reports
long-standing diarrhea. In addition, laboratory tests show low levels of 25hydroxyvitamin D, calcium, and phosphorus and elevated alkaline phosphatase. A second bone biopsy, which was not decalcified, shows
uncalcified osteoid on all the bone surfaces. On the basis of these data, the
most likely diagnosis would be
a.
b.
c.
d.
e.
Osteoporosis
Osteomalacia
Scurvy
Paget’s disease
Hypoparathyroidism
This page intentionally left blank.
BLOCK 3
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
BLOCK 3
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Questions
3-1. A 52-year-old white woman with breast cancer receiving adjuvant therapy presents with back pain that intensifies on movement and pain over the
L1 vertebral body when she coughs and that radiates down her left lower
extremity to her leg and foot. The most likely etiology of this disorder is
a.
b.
c.
d.
Paraneoplastic disorder
Trauma to the lumbar disk
Muscular spasm of the intercostal muscles
Possible spinal cord compression
3-2. An obese 18-year-old male patient presents with small, firm testes, a
small penis, little axillary and and facial hair, azoospermia, gynecomastia,
and elevated levels of plasma gonadotropins. He has had difficulty in social
adjustment throughout high school, but this has worsened and he has been
referred for genetic and endocrine screening. The karyotype from periphBarr bodies?
eral blood leukocytes would most likely show
a.
b.
c.
d.
e.
No
One
Two
Three
Four
49
50
Clinical Vignettes for the USMLE Step 1
3-3. A nine-year-old boy is diagnosed with acute lymphoblastic leukemia.
He is maintained on methotrexate. A recent platelet count is below normal,
and a stool guaiac is 4+. Which of the following agents should be administered to counteract methotrexate toxicity?
a.
b.
c.
d.
e.
N-acetyl-L-cysteine
Vitamin K
Penicillamine
Leucovorin
Deferoxamine
3-4. An individual has difficulty in adjusting his head, especially after he
changes his posture. The most likely pathway affected that might cause this
deficit is the
a.
b.
c.
d.
e.
Lateral vestibulospinal tract
Medial vestibulospinal tract
Medial reticulospinal tract
Lateral reticulospinal tract
Rubrospinal tract
3-5. A 27-year-old female has just returned from a trip to Southeast Asia.
In the past 24 hours, she has developed shaking, chills, and a temperature
of 104°F. A blood smear reveals Plasmodium vivax. Which of the following
agents should be used to eradicate the extraerythrocytic phase of the
organism?
a.
b.
c.
d.
e.
Primaquine
Pyrimethamine
Quinacrine
Chloroquine
Chloroguanide
3-6. During a viral infection, a 23-year-old female develops enlarged lymph
nodes at multiple sites (lymphadenopathy). A biopsy from one of these
enlarged lymph nodes reveals a proliferation of reactive T immunoblasts,
cells that have prominent nucleoli. These reactive T cells are most likely to be
found in which one of the following regions of the lymph node?
a.
b.
c.
d.
e.
Hilum
Medullary sinuses
Paracortex
Primary follicles
Secondary follicles
Block 3
Questions
51
3-7. An immunocompromised person with history of seizures had an MRI
that revealed a temporal lobe lesion. Brain biopsy results showed multinucleated giant cells with intranuclear inclusions. The most probable cause of
the lesion is
a.
b.
c.
d.
e.
Hepatitis C virus
Herpes simplex virus
Listeria monocytogenes
Coxsackievirus
Parvovirus
3-8. A 55-year-old woman presents with pain in her right hip and thigh.
The pain started approximately six months ago and is a deep ache that
worsens when she stands or walks. Your examination reveals increased
warmth over the right thigh. The only laboratory abnormalities are alkaline
phosphatase 656 IU/L (normal 23 to 110 IU/L), elevated 24-h urine
hydroxyproline, and osteocalcin 13 ng/mL (normal 6 ng/mL). X-ray of hips
and pelvis shows osteolytic lesions and regions with excessive osteoblastic
activity. Bone scan shows significant uptake in the right proximal femur.
Which of the following would you include in your differential diagnosis?
a.
b.
c.
d.
e.
Paget’s disease
Multiple myeloma
Osteomalacia
Osteoporosis
Hypoparathyroidism
52
Clinical Vignettes for the USMLE Step 1
3-9. Allen is a 30-year-old bachelor who frequents singles bars. He is cautious and always uses a condom in his sexual encounters. Recently, he has
felt “off,” experiencing a sore throat, malaise, and a slight fever. When you
see him in your office, he has a few swollen lymph nodes and has a large
palpable structure in the left upper abdomen indicated by the * in the
accompanying radiograph. He had a positive monospot test and an elevated sedimentary rate. Your diagnosis is infectious mononucleosis. The
structure you palpated was
a.
b.
c.
d.
e.
An enlarged liver (hepatomegaly)
An enlarged spleen (splenomegaly)
The stomach
A tumor of the liver
Liver cirrhosis
Block 3
Questions
53
3-10. A woman tests positive for pregnancy. In order for the pregnancy to
proceed uneventfully, which of the following must occur?
a.
b.
c.
d.
e.
The corpus luteum must secrete progesterone to sustain the endometrium
The pituitary must secrete hCG to maintain the corpus luteum
The pituitary must secrete prolactin to sustain the placenta
The placenta must secrete FSH to maintain ovarian function
The placenta must secrete LH to maintain ovarian function
3-11. A 4-year-old boy presents with a history of numerous fractures that
are not related to excessive trauma. Physical examination reveals evidence
of previous fractures along with abnormally loose joints, decreased hearing, and blue scleras. X-rays of the boy’s arms reveal the bones to be
markedly thinned. What is the correct diagnosis?
a.
b.
c.
d.
e.
Osteopetrosis
Osteoporosis
Osteomalacia
Osteogenesis imperfecta
Osteitis deformans
3-12. A 17-year-old girl presents with cervical lymphadenopathy, fever,
and pharyngitis. Infectious mononucleosis is suspected. The most rapid
and clinically useful test to make this diagnosis is
a.
b.
c.
d.
e.
IgM antibody to viral core antigen (VCA)
IgG antibody to VCA
Antibody to Epstein-Barr nuclear antigen (EBNA)
Culture
C reactive protein (CRP)
3-13. A 76-year-old female with an eight-year history of CHF that has
been well controlled with digoxin and furosemide develops recurrence of
dyspnea on exertion. On physical examination, she has sinus tachycardia,
rales at the base of both lungs, and 4+ pitting edema of the lower extremities. Which agent could be added to her therapeutic regimen?
a.
b.
c.
d.
e.
Dobutamine
Hydralazine
Minoxidil
Prazosin
Enalapril
54
Clinical Vignettes for the USMLE Step 1
3-14. A 30-year-old woman undergoes surgery for a very large, but fortunately benign, brain tumor. For 2 days after the surgery she is unable to
perform certain previously learned motor functions. This disorder is called
a.
b.
c.
d.
e.
Apraxia
Aphasia
Abulia
Anomia
Alexia
3-15. A 50-year-old man asks for help in establishing an effective weight
loss program. He has been 40 lbs overweight for several years. In planning
a weight loss intervention, the most effective self-management procedure is
a.
b.
c.
d.
e.
Information control
Self-monitoring
Self-punishment
Self-reward
Enlisting social support
3-16. A patient presents in her fifth pregnancy with a history of numbness
and tingling in her right thumb and index finger during each of her previous four pregnancies. Currently, the same symptoms are constant,
although generally worse in the early morning. Symptoms could be somewhat relieved by vigorous shaking of the wrist. Neurologic examination
revealed atrophy and weakness of the abductor pollicis brevis, the opponens pollicis, and the first two lumbrical muscles. Sensation was decreased
over the lateral palm and the volar aspect of the first three digits. Numbness and tingling were markedly increased over the first three digits and
the lateral palm when the wrist was held in flexion for 30 s. The symptoms
suggest damage to
a.
b.
c.
d.
e.
The radial artery
The median nerve
The ulnar nerve
Proper digital nerves
The radial nerve
Block 3
Questions
55
3-17. A 3-year-old female ingests a bottle of aspirin by accident. Among
the therapeutic interventions, which of the following should be included?
a.
b.
c.
d.
e.
Dimercaprol
Deferoxamine
Penicillamine
Na2EDTA
Activated charcoal
3-18. A 45-year-old woman veterinarian who is a faculty member at the
nearby veterinary school comes to your office with complaints of a flulike
syndrome of 9 days’ duration including persistent fever for all 9 days,
extreme fatigue, and severe headache. She has a dry cough, an increased
white count, and thrombocytopenia. Which one of the following is the
likely cause of her infection?
a.
b.
c.
d.
e.
Influenzavirus
Mycoplasma pneumoniae
Chlamydia psittaci
Coxiella burnetii
Chlamydia pneumoniae
3-19. A 30-year-old man with recently developed AIDS is referred to you,
as a primary care physician. What is apt to be the most prominent psychosocial factor or reaction that you can expect from him and perhaps help
prevent?
a.
b.
c.
d.
e.
Loss of independence
Fear of losing confidentiality
Guilt
Depressed mood
Suicidal thoughts
3-20. A patient complains that he cannot move his right eye to the right
and that the right side of his face is expressionless. The likely locus of the
lesion is the
a.
b.
c.
d.
e.
Dorsal aspect of the medulla
Ventromedial medulla
Dorsal pons
Ventromedial pons
Medial midbrain
56
Clinical Vignettes for the USMLE Step 1
3-21. A young boy is being evaluated for developmental delay, mild
autism, and mental retardation. Physical examination reveals the boy to
have large, everted ears and a long face with a large mandible. He is also
found to have macroorchidism (large testes), and extensive workup reveals
multiple tandem repeats of the nucleotide sequence CGG in his DNA.
Which one of the following is the correct diagnosis for this patient?
a.
b.
c.
d.
e.
Fragile X syndrome
Huntington’s chorea
Myotonic dystrophy
Spinal-bulbar muscular atrophy
Ataxia-telangiectasia
Block 3
Questions
57
3-22. An AIDS patient presents to his primary care physician with a
2-week history of watery, nonbloody diarrhea. This stool revealed an organism which can be seen in the figure below. The most likely diagnosis is
(Reproduced, with permission, from Garcia LS: Laboratory Methods for Diagnosis of
Parasitic Infection. In Baron EJ and Finegold SM: Diagnostic Microbiology, 8/e,
St. Louis, Mosby-Year Book: 1990.)
a.
b.
c.
d.
e.
Cyclospora
Cryptosporidium
Enterocytozoon
Yeast
Acid-fast bacilli
58
Clinical Vignettes for the USMLE Step 1
3-23. A 55-year-old female with a blood pressure of 170/105 mmHg has
pitting edema of the lower extremities and an elevated serum creatinine
associated with a normal serum potassium. Which of the following agents
is contraindicated in this patient?
a.
b.
c.
d.
e.
Triamterene
Hydrochlorothiazide
Metolazone
Ethacrynic acid
Acetazolamide
3-24. Several days following a myocardial infarction, a 51-year-old male
develops the sudden onset of a new pansystolic murmur along with a diastolic flow murmur. Workup reveals increased left atrial pressure that
develops late in systole and extends into diastole. These abnormalities in
this individual are most likely the result of
a.
b.
c.
d.
e.
Aneurysmal dilation of the left ventricle
Obstruction of the aortic valve
Rupture of the left ventricle wall
Rupture of a papillary muscle
Thrombosis of the left atrial cavity
3-25. An adolescent female develops hemiballismus (repetitive throwing
motions of the arms) after anesthesia for a routine operation. She is tall and
lanky, and it is noted that she and her sister both had previous operations
for dislocated lenses of the eyes. The symptoms are suspicious for the disease homocystinuria (236300). Which of the statements below is descriptive of this disease?
a.
b.
c.
d.
e.
Patients may be treated with dietary supplements of vitamin B12
Patients may be treated with dietary supplements of vitamin C
There is deficient excretion of homocysteine
There is increased excretion of cysteine
There is a defect in the ability to form homocysteine from methionine by methylation
Block 3
Questions
59
YOU SHOULD HAVE COMPLETED APPROXIMATELY
25 QUESTIONS AND HAVE 30 MINUTES REMAINING.
3-26. A woman, recently returned from Africa, complains of having
paroxysmal attacks of chills, fever, and sweating; these attacks last a day or
two at a time and recur every 36 to 48 h. Examination of a stained blood
specimen reveals ringlike and crescent-like forms within red blood cells.
The infecting organism most likely is
a.
b.
c.
d.
e.
Plasmodium falciparum
Plasmodium vivax
Trypanosoma gambiense
Wuchereria bancrofti
Schistosoma mansoni
60
Clinical Vignettes for the USMLE Step 1
3-27. An adult with mild, chronic anemia does not respond to iron supplementation. Blood is drawn and the red cell hemoglobin is analyzed.
Which of the following results is most likely if the patient has an altered
hemoglobin molecule (hemoglobinopathy)?
a. Several proteins but only one red protein detected by high-performance liquid
chromatography (HPLC)
b. Two proteins detected in normal amounts by western blotting
c. Several proteins and two red proteins separated by native gel electrophoresis
d. Two labeled bands a slight distance apart after SDS-gel electrophoresis and reaction with labeled antibody to α- and β-globin
e. A reddish mixture of proteins retained within a dialysis membrane
3-28. A medical student presents to the emergency room with a two-day
history of severe vomiting and orthostatic hypotension. What kind of
metabolic abnormalities would you expect?
a.
b.
c.
d.
e.
Hypokalemia, hypochloremia, and metabolic acidosis
Hyperkalemia, hyperchloremia, and metabolic alkalosis
Normal serum electrolytes and metabolic acidosis
Normal serum electrolytes and metabolic alkalosis
Hypokalemic, hypochloremic, metabolic alkalosis
3-29. Two parents are both affected with albinism (203100, 203200), but
have a normal child. Which of the following terms best applies to this situation?
a.
b.
c.
d.
e.
Allelic heterogeneity
Locus heterogeneity
Variable expressivity
Incomplete penetrance
New mutation
Block 3
Questions
61
3-30. A 24-year-old female presents with a 2-year history of infertility. An
endometrial biopsy is obtained approximately 5 to 6 days after the predicted time of ovulation. This biopsy specimen reveals secretory endometrium, but there is a significant difference (asynchrony) between the
estimated chronologic menstrual date and the estimated histologic menstrual date. No proliferative endometrium is seen. Based on this information, what is the correct diagnosis for this biopsy specimen?
a.
b.
c.
d.
Anovulatory cycle (no corpus luteum formed)
Inadequate luteal phase (decreased functioning of the corpus luteum)
Irregular shedding (prolonged functioning of the corpus luteum)
Normal endometrium during the follicular phase of the cycle (no corpus
luteum formed)
e. Normal endometrium during the luteal phase of the cycle (normal corpus
luteum)
3-31. During a visit to her gynecologist, a patient reports she received vitamin A treatment for her acne unknowingly during the first two months of
an undetected pregnancy. Which organ systems in the developing fetus are
most likely to be affected?
a.
b.
c.
d.
e.
The digestive system
The endocrine organs
The respiratory system
The urinary and reproductive systems
The skeletal and central nervous systems
3-32. A 32-year-old cancer patient, who has smoked two packs of cigarettes a day for 10 years, presents a decreased pulmonary function test.
Physical examination and chest x-rays suggest preexisting pulmonary disease. Of the following drugs, which is best not prescribed?
a.
b.
c.
d.
e.
Vinblastine
Doxorubicin
Mithramycin
Bleomycin
Cisplatin
62
Clinical Vignettes for the USMLE Step 1
3-33. In the operating room, a child receives succinylcholine as a muscle
relaxant to facilitate intubation and anesthesia. The operation proceeds
until it is time for recovery, when the child does not begin breathing. A hurried discussion with the father discloses no additional problems in the family, but he does say that he and his wife are first cousins. The most likely
possibility is
a. An autosomal dominant disorder that interferes with succinylcholine metabolism
b. An autosomal recessive disorder that interferes with succinylcholine metabolism
c. An X-linked disorder that interferes with succinylcholine metabolism
d. A lethal gene transmitted through consanguinity that affects the respiratory system
e. Mismanagement of halothane anesthesia during the operation
3-34. A 12-year-old boy is brought to your office by his mother because
he developed a painless rash on his face and legs. The rash began as red
papules and then became vesicular and pustular and finally it coalesced in
honeycomb-like crusts. The boy does not have fever, but he does have several insect bites and he is unwashed and dressed in dirty clothes. This rash
is likely to be
a.
b.
c.
d.
e.
Herpes simplex
Shingles
Impetigo
Scarlet fever
Erysipelas
3-35. A patient has all the gastrointestinal symptoms of infection with
hepatitis A virus (HAV), yet all the tests for HAV-IgG and HAV-IgM are nonreactive. A possible cause of this infection is
a.
b.
c.
d.
e.
Hepatitis B surface antigen
Hepatitis C
Hepatitis D
Hepatitis E
Rotavirus
Block 3
Questions
63
3-36. A middle-aged man is admitted to the hospital for further workup of
a suspected malignancy. Which of the following defense mechanisms is
most likely to be observed in this individual?
a.
b.
c.
d.
e.
Rationalization
Projection
Displacement
Sublimation
Denial
3-37. A 68-year-old man goes to a sleep clinic after he has repeated
episodes of loud snoring during sleep coupled with sudden periods of restlessness and cessation of breathing. After extensive analysis, the physicians
concluded that the patient’s problem was not a result of obstructive sleep.
Instead, it was judged that this condition reflected central sleep apnea due
to loss of chemoreceptor sensitivity of the neuronal control mechanisms
governing respiration. The most likely site within the CNS that is most
closely associated with these effects is the
a.
b.
c.
d.
e.
Dorsal horn of the thoracic spinal cord
Reticular formation of the medulla
Midbrain periaqueductal gray
Hippocampal formation
Border of occipital and parietal lobes
3-38. A 26-year-old man contracted viral influenza with an unremitting
fever of 39.5°C (103°F) for three days. Because spermatogenesis cannot
occur above a scrotal temperature of 35.5°C (96°F), he was left with no
viable sperm on his recovery. The time required for spermatogenesis,
spermiogenesis, and passage of viable sperm to the epididymis is approximately
a.
b.
c.
d.
e.
3 days
1 week
5 weeks
2 months
4 months
64
Clinical Vignettes for the USMLE Step 1
3-39. A 35-year-old male has renal stones and increased calcium (Ca) in
the urine that is associated with normal serum Ca and parathyroid hormone levels. Which of the following agents could be used to treat this
patient?
a.
b.
c.
d.
e.
Furosemide
Acetazolamide
Triamterene
Hydrochlorothiazide
Vasopressin
Block 3
Questions
65
3-40. The MRI scan in the figure below reveals a large chromophobe adenoma (T) of the pituitary that impinges on the adjoining brain tissue. This
tumor caused a
a.
b.
c.
d.
e.
Binasal hemianopsia
Bitemporal hemianopsia
Loss of the accommodation reflex
Loss of the pupillary light reflex
Loss of conjugate gaze
66
Clinical Vignettes for the USMLE Step 1
3-41. A middle-aged man has undergone a series of biofeedback sessions
to control brief elevations in blood pressure under stressful situations. The
most important component of this treatment is
a.
b.
c.
d.
e.
Feelings
Information
Motivation
Attitude
Interpersonal relations
3-42. A 67-year-old male is found on rectal examination to have a single,
hard, irregular nodule within his prostate. A biopsy of this lesion reveals
the presence of small glands lined by a single layer of cells with enlarged,
prominent nucleoli. From what portion of the prostate did this lesion most
likely originate?
a.
b.
c.
d.
e.
Anterior zone
Central zone
Peripheral zone
Periurethral glands
Transition zone
3-43. A 60-year-old woman recently was widowed when her husband
died suddenly in an acute myocardial infarction. You are seeing her in a
primary care practice for a variety of nonspecific complaints. She is clearly
in the midst of grieving for her husband. She is likely to have which of the
following physiologic changes?
a.
b.
c.
d.
e.
Decreased responsiveness of lymphocytes to mitogens
Decreased corticotrophin-releasing hormone levels
Decreased responsiveness of serotonin-3 receptors
Decreased sensitivity of α-adrenergic receptors
Decreased antibody titers to Epstein-Barr virus
Block 3
Questions
67
3-44. A 22-year-old woman marathon runner comes into the office complaining of amenorrhea for 8 months. There has been no weight change,
and the serum pregnancy test is negative. She has never been pregnant.
Menarche was at 13 years of age, and she had monthly menses until 8
months ago. Physical exam shows a women who is 66 inches tall, 90
pounds, and is otherwise fully normal. Why does she have amenorrhea?
a.
b.
c.
d.
e.
Hypothyroidism
Prolactinoma
Early menopause
Resistance to LH and FSH
Excessive exercise
3-45. A 9-year-old child is brought to the emergency room with the chief
complaint of enlarged, painful axillary lymph nodes. The resident physician
also notes a small, inflamed, dime-sized lesion surrounding what appears to
be a small scratch on the forearm. The lymph node is aspirated and some pus
is sent to the laboratory for examination. A Warthin-Starry silver impregnation stain reveals many highly pleomorphic, rod-shaped bacteria. The most
likely cause of this infection is
a.
b.
c.
d.
e.
Y. pestis
Yersinia enterocolitica
Mycobacterium scrofulaceum
B. canis
Bartonella henselae
3-46. A man, the victim of several knife wounds to the abdomen during a
barroom brawl, subsequently developed a direct inguinal hernia. Damage
to which of the following nerves is most likely responsible for the predisposing weakness of the abdominal wall?
a.
b.
c.
d.
e.
Genitofemoral nerve
Ilioinguinal nerve
The subcostal nerve
Pelvic splanchnic nerves
The nerve of the tenth intercostal space (T10)
68
Clinical Vignettes for the USMLE Step 1
3-47. A 10-year-old male displays hyperactivity and is unable to focus on
his schoolwork because of an inability to focus on the activity. Which of the
following might prove effective in this patient?
a.
b.
c.
d.
e.
f.
Methylphenidate
Terbutaline
Dobutamine
Pancuronium
Prazosin
Scopalamine
3-48. A full-term male infant displays projectile vomiting 1 h after suckling. There is failure to gain weight during the first two weeks. The vomitus
is not bile-stained and no respiratory difficulty is evident. Examination
reveals an abdomen neither tense nor bloated. The most probable explanation is
a.
b.
c.
d.
e.
Congenital hypertrophic pyloric stenosis
Duodenal atresia
Patent ileal diverticulum
Imperforate anus
Tracheoesophageal fistula
3-49. You have been designated as coordinator of construction of a bone
marrow transplant unit (BMTU). There will be extensive removal of walls
and floors in order to install the laminar flow rooms required for a BMTU.
From the standpoint of frequency and lethality, which one of the following
fungi should be your biggest concern?
a.
b.
c.
d.
e.
Aspergillus
Candida
Wangiella
Cryptococcus
Blastomyces
3-50. A patient on long-term lithium comes into your office complaining
of polyuria; you would expect his serum sodium to be
a.
b.
c.
d.
Elevated because he has central diabetes insipidus
Elevated because he has nephrogenic diabetes insipidus
Nearly normal because he is drinking increased amounts of water
Low because he is suffering from psychogenic polydipsia
BLOCK 4
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
BLOCK 4
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Questions
4-11. A 38-year-old female presents with the new onset of multiple purpuric skin lesions. Two years ago she developed late-onset asthma and mild
hypertension. Laboratory examination reveals an increase in the number of
eosinophils in the peripheral blood (peripheral eosinophilia), and a biopsy
from one of the purpuric skin lesions reveals leukocytoclastic vasculitis. No
perivascular IgA deposits are found, and no antineutrophil cytoplasm
autoantibodies are present. Which one of the listed disorders is the best
diagnosis for this individual?
a.
b.
c.
d.
e.
Churg-Strauss syndrome
Henoch-Schönlein purpura
Macroscopic polyarteritis nodosa
Microscopic polyangiitis
Wegener’s granulomatosis
71
72
Clinical Vignettes for the USMLE Step 1
4-2. A 28-year-old woman presents to the office with 2 days of abdominal
pain and a positive pregnancy test. Her last menstrual period was 9 weeks
ago. She reports no dysuria. She reports a history of two episodes of pelvic
inflammatory disease. Which of these is the most likely cause of the abdominal pain?
a.
b.
c.
d.
e.
Endometriosis
Urinary tract infection
Ectopic pregnancy
Placental abruption
Premenstrual syndrome
4-3. Sudden standing evokes the baroreceptor reflex. Which one of the
following will be greater after a person suddenly stands up than it was
before the person stood?
a.
b.
c.
d.
e.
The end-diastolic volume
The renal blood flow
The venous return
The pulse pressure
The ejection fraction
Questions 4-4 to 4-5
A 45-year-old plumber presented in the clinic complaining of longstanding pain in the elbow. Subsequent examination revealed normal flexion/
extension at both the elbow and the wrist but weakened abduction of the
thumb and extension at the metacarpophalangeal joints of the fingers.
These symptoms were found to be caused by entrapment of the posterior
interosseus nerve.
4-4. Which of the following muscles could be expected to demonstrate
normal contraction?
a.
b.
c.
d.
e.
Extensor indices
Extensor digitorum
Extensor carpi radialis longus
Abductor pollicis longus
Extensor digit minimi
Block 4
Questions
73
4-5. Which of the following muscles could itself cause entrapment of the
posterior interosseus nerve?
a.
b.
c.
d.
e.
Extensor carpi ulnaris
Extensor indices
Anconeus
Extensor digitorum
Supinator
4-6. A 72-year-old female with a long history of anxiety treated with
diazepam decides to triple her dose because of increasing fearfulness about
“environmental noises.” Several days after her attempt at self-prescribing,
her neighbor finds her to be extremely lethargic and nonresponsive. On
examination, she is found to be stuporous and have diminished reaction to
pain and decreased reflexes. Her respiratory rate is 8 breaths per minute
(BPM), and she has shallow respirations. Which antidote could be given to
reverse these findings?
a.
b.
c.
d.
Naltrexone
Physostigmine
Pralidoxime
Flumazenil
74
Clinical Vignettes for the USMLE Step 1
4-7. A 22-year-old female presents with fever, weight loss, night sweats,
and painless enlargement of several supraclavicular lymph nodes. A biopsy
from one of the enlarged lymph nodes is shown in the photomicrograph
below. The binucleate or bilobed giant cell with prominent acidophilic
“owl-eye” nucleoli shown is a
a.
b.
c.
d.
e.
Call-Exner cell
Hürthle cell
Reed-Sternberg cell
Sézary cell
Strap cell
4-8. A 25-year-old female post–renal transplant shows signs of acute renal
allograph rejection. Of the following agents, which should be administered?
a.
b.
c.
d.
e.
Interferon α
Aldesleukin
Muromonab-CD3
Sargramostim
Filgrastim
Block 4
Questions
75
4-9. Upon examination, a patient is unable to move his right eye medially.
The lesion is likely to be located in the
a.
b.
c.
d.
e.
Dorsal medulla
Ventromedial medulla
Dorsal pons
Ventromedial pons
Medial midbrain
4-10. A young woman has recently completed an inpatient program for
alcohol dependence. Using the classical conditioning model, the patient’s
risk of relapse is increased if she is
a. Maintained in an environment free of alcohol-associated stimuli
b. Provided therapeutic strategies to extinguish alcohol-compensatory conditioned responses
c. Returned to an environment different from the one in which the dependence
was acquired
d. Provided procedures to extinguish conditioned associations between aversive
affective states and alcohol
e. Allowed to substitute the use of other nonalcoholic drugs when negative affective states occur
4-11. A 24-year-old male visited the community clinic complaining of a
draining abscess on his anterior thigh. Subsequent testing revealed an
active tuberculosis infection localized in the lumbar vertebrae. The spread
of infection most likely occurred via
a.
b.
c.
d.
The ischiorectal fossa
The sheath of the psoas muscle
The inguinal ligament
A paracolic gutter
4-12. A 65-year-old male has a blood pressure of 170/105 mmHg. Which
of the following would be effective in lowering this patient’s blood pressure?
a.
b.
c.
d.
e.
f.
Methylphenidate
Terbutaline
Dobutamine
Pancuronium
Prazosin
Scopalamine
76
Clinical Vignettes for the USMLE Step 1
4-13. A middle-aged patient with an elevated serum creatinine, hypertension, and mild anemia comes to you for evaluation. Urine dipstick shows
trace protein without red cells or cellular casts. A 24-h urine collection
reveals 5 g of protein. The most likely etiology is
a.
b.
c.
d.
Focal segmental sclerosis
Hypertensive nephrosclerosis
Amyloidosis
Multiple myeloma
4-14. Bleeding time is determined by nicking the skin superficially with a
scalpel blade and measuring the time required for hemostasis. It will be
markedly abnormal (prolonged) in a person who
a.
b.
c.
d.
e.
Lacks factor VIII
Cannot absorb vitamin K
Has liver disease
Takes large quantities of aspirin
Takes coumarin derivatives
4-15. A 3-year-old child is brought into the ER while you are on duty. She
is cold and clammy and is breathing rapidly. She is obviously confused and
lethargic. Her mother indicates she has accidentally ingested automobile
antifreeze while playing in the garage. Following gastrointestinal lavage
and activated charcoal administration, one of the treatments you immediately initiate involves
a.
b.
c.
d.
e.
Intravenous infusion of oxalic acid
Nasogastric tube for ethanol administration
Flushing out the bladder via a catheter
Intramuscular injection of epinephrine
Simply waiting and measuring vital signs
4-16. An obstetrician sees a pregnant patient who was exposed to rubella
virus in the eighteenth week of pregnancy. She does not remember getting
a rubella vaccination. The best immediate course of action is to
a. Terminate the pregnancy
b. Order a rubella antibody titer to determine immune status
c. Reassure the patient because rubella is not a problem until after the thirtieth
week
d. Administer rubella immune globulin
e. Administer rubella vaccine
Block 4
Questions
77
4-17. The bone marrow biopsy shown in the photomicrograph below was
performed because of splenomegaly and anemia in an adult. On the basis
of the appearance of the bone marrow core, the most likely diagnosis is
a.
b.
c.
d.
e.
Chronic myeloid leukemia (CML)
Aplastic anemia
Acute leukemia
Myeloid metaplasia with myelofibrosis
Microangiopathic hemolytic anemia
4-18. A 60-year-old female with deep-vein thrombosis (DVT) is given a
bolus of heparin, and a heparin drip is also started. Thirty minutes later,
she is bleeding profusely from the intravenous site. The heparin is stopped,
but the bleeding continues. You decide to give protamine to reverse the
adverse effect of heparin. How does protamine act?
a.
b.
c.
d.
It causes hydrolysis of heparin
It changes the conformation of antithrombin III to prevent binding to heparin
It activates the coagulation cascade, overriding the action of heparin
It combines with heparin as an ion pair, thus inactivating it
78
Clinical Vignettes for the USMLE Step 1
4-19. Leukocyte samples isolated from the blood of a newborn infant are
homogenized and incubated with ganglioside GM2. Approximately 47% of
the expected normal amount of N-acetylgalactosamine is liberated during
the incubation period. These results indicate that the infant
a.
b.
c.
d.
e.
Is a heterozygote (carrier) for Tay-Sachs disease
Is homozygous for Tay-Sachs disease
Has Tay-Sachs syndrome
Will most likely have mental deficiency
Has relatively normal β-N-acetylhexosaminidase activity
4-20. A 70-year-old man presents to you because he has not been feeling
well for several months. He mainly complains of malaise and achiness. He
takes ibuprofen occasionally for these symptoms. His urine shows protein
and erythrocyte casts. A 24-h urine shows 1 g of protein per day. His creatinine clearance is 24 mL/min. About 4 months ago, his serum creatinine
was normal. The most likely diagnosis is
a.
b.
c.
d.
Amyloidosis
Light chain deposition disease
Nonsteroidal induced interstitial nephritis
Vasculitis
4-21. A 60-year-old male complains of severe headaches, nausea, dizziness, and a diminution in vision. He has a decrease in oxygen (O2)-carrying
capacity without a change in the PO2 of arterial blood. Which of the following might account for these findings?
a.
b.
c.
d.
e.
Sulfur dioxide
Ozone
Nitrogen dioxide
Carbon monoxide (CO)
Methane
Questions 4-22 through 4-23
A 46-year-old bakery worker is admitted to a hospital in acute distress.
She has experienced severe abdominal pain, nausea, and vomiting for two
days. The pain, which is sharp and constant, began in the epigastric region
and radiated bilaterally around the chest to just below the scapulas. Subsequently, the pain became localized in the right hypochondrium. The
patient, who has a history of similar attacks after hearty meals over the past
Block 4
Questions
79
five years, is moderately overweight and the mother of four. Palpation
reveals marked tenderness in the right hypochondriac region and some
rigidity of the abdominal musculature. An x-ray without contrast medium
shows numerous calcified stones in the region of the gallbladder. The
patient shows no sign of icterus (jaundice).
4-22. Diffuse pain referred to the epigastric region and radiating circumferentially around the chest is the result of afferent fibers that travel via
which of the following nerves?
a.
b.
c.
d.
Greater splanchnic
Intercostal
Phrenic
Vagus
4-23. The above patient receives a general anesthetic in preparation for a
cholecystectomy. A right subcostal incision is made, which begins near the
xiphoid process, runs along and immediately beneath the costal margin to
the anterior axillary line, and transects the rectus abdominis muscle and
rectus sheath. At the level of the transpyloric plane, the anterior wall of the
sheath of the rectus abdominis muscle receives contributions from the
a. Aponeuroses of the internal and external oblique muscles
b. Aponeuroses of the transversus abdominis and internal oblique muscles
c. Aponeuroses of the transversus abdominis and internal and external oblique
muscles
d. Transversalis fascia
e. Transversalis fascia and aponeurosis of the transversus abdominis muscle
4-24. A 30-year-old male with a two-year history of chronic renal failure
requiring dialysis consents to transplantation. A donor kidney becomes
available. He is given cyclosporine to prevent transplant rejection just before
surgery. What is the most likely adverse effect of this drug?
a.
b.
c.
d.
e.
Bone marrow depression
Nephrotoxicity
Oral and GI ulceration
Pancreatitis
Seizures
80
Clinical Vignettes for the USMLE Step 1
4-25. A 47-year-old male presents with the sudden onset of fever, chills,
and dysuria. During the review of symptoms you discover that he has no
history of recurrent urinary tract infections. Rectal examination finds that
the prostate gland is very sensitive and examination is painful. What is the
most likely diagnosis for this patient?
a.
b.
c.
d.
e.
Acute prostatitis
Chronic bacterial prostatitis
Chronic abacterial prostatitis
Granulomatous prostatitis
Benign prostatic hyperplasia
Block 4
Questions
81
YOU SHOULD HAVE COMPLETED APPROXIMATELY
25 QUESTIONS AND HAVE 30 MINUTES REMAINING.
4-26. An 82-year-old woman presents with headaches, visual disturbances, and muscle pain. A biopsy of the temporal artery is shown in the
associated photomicrograph. The next course of action is to
a.
b.
c.
d.
e.
Administer corticosteroids
Verify with a repeat biopsy
Administer anticoagulants
Perform angiography
Order a test of the erythrocyte sedimentation rate
82
Clinical Vignettes for the USMLE Step 1
4-27. The following test results were observed in a woman tested in November who reported being in the woods in Pennsylvania during the past summer, was bitten by a tick, and now has Bell’s palsy: Lyme IgG antibody
1:1280; Lyme IgM antibody negative. Which one of the following courses of
action is most appropriate?
a. Order tests for syphilis (VDRL, FTA-ABS) because there are cross-reactions
reported with Borrelia burgdorferi
b. Ask the patient if she has a severe headache
c. Consider treatment of the patient with an appropriate antibiotic such as tetracycline
d. Ask the patient if she has had a urinary tract infection with E. coli
e. Ignore the results because there is no Lyme disease in Pennsylvania
Block 4
Questions
83
4-28. Your patient reports he spent two weeks on a desert island as part of
a television survival show. It rained and was cool the last five days and he
developed a cough. He is now in the ER with a productive cough that produces rusty and bloodstained sputum. He also complains of significant
pleural pain. You suspect a pneumococcal lobar pneumonia. From this CT
scan at the T4 level, which lung lobe (indicated by the *) is involved with
the pneumonia?
a.
b.
c.
d.
e.
Right upper lobe
Right middle lobe
Right lower lobe
Left upper lobe
Left lower lobe
84
Clinical Vignettes for the USMLE Step 1
4-29. A 60-year-old male with AIDS develops a systemic fungal infection
that is treated with fluconazole. What is the mechanism of action of fluconazole?
a.
b.
c.
d.
It inhibits ergosterol synthesis
It inhibits DNA synthesis
It inhibits peptidoglycan synthesis
It inhibits protein synthesis
4-30. You are working up a middle-aged patient who has moderate essential hypertension. You start the patient on an initial pharmacologic requiem
of an ACE inhibitor. Which behavioral risk factors would you approach
first in your long-term follow-up of the patient?
a.
b.
c.
d.
Type A personality
Dietary salt intake
Stress in the workplace
Obesity
4-31. A section of tissue from the foot of a person assumed to have eumycotic mycetoma shows a white, lobulated granule composed of fungal
hyphae. In the United States, the most common etiologic agent of this condition is a species of
a.
b.
c.
d.
e.
Acremonium
Nocardia
Actinomyces
Pseudallescheria (Petriellidium)
Madurella
4-32. A 55-year-old man who is a longtime alcoholic comes to the emergency room after vomiting small amounts of bright red blood four times
today. Your differential diagnosis is constructed around causes of bleeding
from the
a.
b.
c.
d.
e.
Colon
Liver and pancreas
Kidneys
Lungs
Upper gastrointestinal (GI) tract
Block 4
Questions
85
4-33. A 5-year-old girl displays decreased appetite, increased urinary frequency, and thirst. Her physician suspects new-onset diabetes mellitus and
confirms that she has elevated urine glucose ketones. Which of the following blood values would be most compatible with diabetic ketoacidosis?
a.
b.
c.
d.
e.
pH
7.05
7.25
7.40
7.66
7.33
Bicarbonate (mM)
16.0
20.0
24.5
37.0
12.0
Arterial PCO2
52
41
39
30
21
4-34. A 71-year-old female presents with the sudden onset of severe lower
back pain. Physical examination reveals severe kyphosis, while an x-ray of
her back reveals a compression fracture of a vertebral body in the lumbar
area along with marked thinning of the bones. Serum calcium, phosphorus, alkaline phosphatase, and parathyroid hormone levels are all within
normal limits. This woman’s bone changes are most likely due to
a.
b.
c.
d.
e.
Osteopetrosis
Osteoporosis
Osteomalacia
Osteitis fibrosa cystica
Osteitis deformans
4-35. A 40-year-old female post–renal transplant has developed evidence
of osteoporosis, most likely due to cyclosporine. Which of the following
agents might replace cyclosporine?
a.
b.
c.
d.
e.
f.
g.
h.
i.
Allopurinol
Asparaginase
Methotrexate
Streptozocin
6-MP
Azathioprine
Pentostatin
Leucovorin
BCG vaccine
86
Clinical Vignettes for the USMLE Step 1
4-36. A medical technologist visited Scandinavia and consumed raw fish
daily for 2 weeks. Six months after her return home, she had a routine
physical and was found to be anemic. Her vitamin B12 levels were below
normal. The most likely cause of her vitamin B12 deficiency anemia is
a.
b.
c.
d.
e.
Excessive consumption of ice-cold vodka
Infection with parvovirus B 19
Infection with the fish tapeworm D. latum
Infection with Yersinia
Cysticercosis
Questions 4-37 to 4-38
As a result of a leg injury, a 30-year-old male developed chronic pain
and was subsequently treated with morphine. Consequently, he developed
an addiction to morphine.
4-37. The predominant site where this effect is mediated is the
a.
b.
c.
d.
e.
Opioid nociceptin receptor
Opioid µ receptor
Opioid δ receptor
Opioid κ receptor
Dopamine D2-receptor
4-38. A region of the brain where this receptor has been shown through
extensive research to be heavily concentrated is the
a.
b.
c.
d.
e.
Mammillary bodies
Precentral gyrus
Midbrain periaqueductal gray
Inferior olivary nucleus
Deep pontine nuclei
Block 4
Questions
87
4-39. A newborn with tachypnea and cyanosis (bluish color) is found to
have a blood pH of 7.1. A serum bicarbonate is measured as 12 mM, but
the blood gas machine that would determine the partial pressures of oxygen (PO2) and carbon dioxide (PCO2) is broken. Recall the pKa of 6.1 for carbonic acid (reflecting the HCO3−/CO2 equilibrium in blood) and the fact
that the blood CO2 concentration is equal to the PCO2 in mmHg (normal
value = 40 mmHg) multiplied by 0.03. Which of the following treatment
strategies is indicated?
a.
b.
c.
d.
e.
Administer oxygen to improve tissue perfusion and decrease metabolic acidosis
Administer oxygen to decrease respiratory acidosis
Increase the respiratory rate to treat respiratory acidosis
Decrease the respiratory rate to treat respiratory acidosis
Administer medicines to decrease renal hydrogen ion excretion
4-40. A butcher, who is fond of eating raw hamburger, develops chorioretinitis; a Sabin-Feldman dye test is positive. This patient is most likely
infected with
a.
b.
c.
d.
e.
Trichinosis
Schistosomiasis
Toxoplasmosis
Visceral larva migrans
Giardiasis
4-41. A teenage girl presents for evaluation of hearing loss in her right ear.
She has a history of at least 12 episodes of otitis media as a child; at least
one time she perforated her ear drum. Her hearing loss is classified as
a.
b.
c.
d.
e.
Conductive deafness
Sensorineural deafness
Central deafness
Tinnitus
Presbycusis
4-42. A 70-year-old female is treated with sublingual nitroglycerin for her
occasional bouts of angina. Which of the following is involved in the action
of nitroglycerin?
a.
b.
c.
d.
e.
α-adrenergic activity
Phosphodiesterase activity
Phosphorylation of light chains of myosin
Norepinephrine release
cGMP
88
Clinical Vignettes for the USMLE Step 1
4-43. A 49-year-old man develops an acute myocardial infarction because
of the sudden occlusion of the left anterior descending coronary artery. The
areas of myocardial necrosis within the ventricle can best be described as
a.
b.
c.
d.
e.
Coagulative necrosis
Liquefactive necrosis
Fat necrosis
Caseous necrosis
Fibrinoid necrosis
Questions 4-44 to 4-45
4-44. The patient whose CT scan is shown in the figure above sustained
an occlusion of a major artery on the left side of the brain. The most prominent deficits will most likely include
a.
b.
c.
d.
e.
A right homonymous hemianopsia only
Aphasia only
A right homonymous hemianopsia coupled with aphasia
Marked intellectual deficits
Marked intellectual deficits coupled with hemiballism
Block 4
Questions
89
4-45. The blood vessel occluded in the above figure is the
a.
b.
c.
d.
e.
Anterior cerebral artery
Middle cerebral artery
Posterior cerebral artery
Posterior choroidal artery
Superior cerebellar artery
4-46. You are designing a weight-reduction program for a patient with
long-term obesity. You wish to use a group of behavioral techniques that
derive from the principle of stimulus control. Which of these instructions
would be consistent with this plan?
a.
b.
c.
d.
e.
Watching TV or reading when eating
Eating only when hungry, not at specific times
Eating in a variety of different places
Shopping for groceries only when hungry
Eating at specific times and places
4-47. A 50-year-old woman executive has for the past 3 months experienced abdominal pain that often is relieved by antacids. Because of the persistent abdominal pain, she consults a gastroenterologist. He does an upper
GI endoscopy and visualizes a duodenal ulcer. Now, the gastroenterologist
should
a.
b.
c.
d.
e.
Biopsy the ulcer
Arrange for a surgeon to operate on the ulcer
Suggest medical treatment of the ulcer
Cauterize the ulcer
Order an abdominal CT scan
4-48. A 15-year-old male comes into the office complaining about a lack
of pubic hair growth. He also informs you that his voice has not yet deepened, and he has no interest in sexual activity. He is an only child. Blood
drawn reveals a very high testosterone level. What is the problem?
a.
b.
c.
d.
e.
Low FSH and LH
High FSH and LH
Androgen insensitivity
Hyperthyroidism
XXY karyotype
90
Clinical Vignettes for the USMLE Step 1
4-49. A 19-year-old female presents with urticaria that developed after she
took aspirin for a headache. She has a history of chronic rhinitis, and physical examination reveals the presence of nasal polyps. This patient is at an
increased risk of developing which one of the following pulmonary diseases following the ingestion of aspirin?
a.
b.
c.
d.
e.
Asthma
Chronic bronchitis
Emphysema
Interstitial fibrosis
Pulmonary hypertension
4-50. A 60-year-old male with hematuria is found to have a small localized tumor of the bladder that is diagnosed as a carcinoma. Which of the
following agents should be given intravesicularly?
a.
b.
c.
d.
e.
f.
g.
h.
i.
Allopurinol
Asparaginase
Methotrexate
Streptozocin
6-MP
Azathioprine
Pentostatin
Leucovorin
BCG vaccine
BLOCK 5
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
BLOCK 5
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Questions
5-1. A 32-year-old male presents with scrotal enlargement. Physical examination, including scrotal transillumination, reveals the presence of a testicular cyst containing clear fluid. This abnormality most likely results from
fluid accumulating within the
a.
b.
c.
d.
e.
Ampulla of the ductus deferens
Appendix testis
Epididymis
Seminal vesicles
Tunica vaginalis
5-2. A patient displays an ipsilateral paralysis of lateral gaze coupled with
a contralateral hemiplegia. A lesion is most likely situated in the
a.
b.
c.
d.
e.
Ventromedial medulla
Dorsomedial medulla
Ventrocaudal pons
Dorsorostral pons
Ventromedial midbrain
93
94
Clinical Vignettes for the USMLE Step 1
5-3. A 47-year-old male presents with pain in the midportion of his chest.
The pain is associated with eating and swallowing food. Endoscopic examination reveals an ulcerated area in the lower portion of his esophagus. Histologic sections of tissue taken from this area reveal an ulceration of the
esophageal mucosa that is filled with blood, fibrin, proliferating blood vessels, and proliferating fibroblasts. Mitoses are easily found, and most of the
cells have prominent nucleoli. Which one of the following correctly
describes this ulcerated area?
a.
b.
c.
d.
e.
Caseating granulomatous inflammation
Dysplastic epithelium
Granulation tissue
Squamous cell carcinoma
Noncaseating granulomatous inflammation
5-4. A 45-year-old obese woman with cholelithiasis presents to the emergency room complaining of nausea and vomiting for 2 days, along with
severe continuous midabdominal pain. She has a low-grade fever and the
ER physician finds that she has a slightly elevated WBC count (12,000) and
an elevated serum amylase. The most likely diagnosis is
a.
b.
c.
d.
e.
Ruptured abdominal aortic aneurysm
Hepatitis
Peptic ulcer disease
Early phase of acute appendicitis
Acute pancreatitis
Block 5
Questions
95
5-5. A 22-year-old male who belongs to a weekend football league was
running with the ball when a defender tackled him mid-lower limb from
the side. After the tackle, he felt that the knee was hurt and went to the
emergency room. From an MRI of the knee, the lateral meniscus is uniformly black; however, the medial meniscus has a tear (lucent area within
the meniscus). Which of the following is the reason why the medial meniscus is more susceptible to damage than the lateral meniscus?
a. The medial meniscus is attached to the popliteus muscle tendon, which can
move into a position making it more susceptible.
b. The medial meniscus is attached to the medial (tibial) collateral ligament,
which holds it relatively immobile, making it more susceptible.
c. The medial meniscus is attached to the anterior cruciate ligament, which holds
it relatively immobile, making it more susceptible.
d. The only reason the medial meniscus is more susceptible to damage is that the
knee usually gets hit laterally, causing more torsion on the medial meniscus.
96
Clinical Vignettes for the USMLE Step 1
5-6. A fur trapper complains of sore muscles, has swollen eyes, and
reports eating bear meat on a regular basis. He is at risk for
a.
b.
c.
d.
e.
Trichinosis
Schistosomiasis
Toxoplasmosis
Visceral larva migrans
Giardiasis
5-7. A newborn female infant develops edema, jaundice, and trouble
breathing. The blood type of the mother is AB negative, while the baby and
the father are both B positive. The mother’s only other pregnancy was unremarkable, and she has never received any blood or blood products. Laboratory examination reveals a positive Coombs (DAT) test. What is the best
diagnosis?
a.
b.
c.
d.
e.
ABO hemolytic disease of the newborn
Hemoglobin H disease
Hyaline membrane disease of the newborn
Hydrops fetalis
Rh hemolytic disease of the newborn
5-8. A 45-year-old female has a bone marrow transplant for treatment of
ovarian cancer. Cyclosporine is given as an immunosuppressant. What is
the mechanism of action of cyclosporine?
a.
b.
c.
d.
e.
Direct destruction of proliferating lymphoid cells
Inhibition of T cell response to cytokines
Inhibition of folic acid metabolism
Inhibition of factors that stimulate T cell growth
Inhibition of enzymes that are related to purine metabolism
5-9. A 60-year-old male has high blood pressure and the diagnosis indicates that it is due in part to retention of water. Which of the following
compounds would most likely relate to this process?
a.
b.
c.
d.
e.
Oxytocin
Serotonin
Histamine
Vasopressin
Somatostatin
Block 5
Questions
97
5-10. A 45-year-old man has a mild heart attack and is placed on diet and
mevastatin therapy. Which of the following will be a result of this therapy?
a.
b.
c.
d.
e.
f.
g.
Low blood glucose
Low blood LDLs
High blood cholesterol
High blood glucose
Low oxidation of fatty acids
Ketosis
Lipolysis
5-11. A 19-year-old pregnant female feels tired and out of pep. Her conjunctivae are pale; laboratory tests show she has a mild normocytic, normochromic anemia with a low serum iron and an increased TIBC
(transferrin iron-binding capacity). Hemoccult tests are negative. Which is
the likely cause of her anemia?
a.
b.
c.
d.
e.
Gastrointestinal bleeding
Iron or folate deficiencies
Autoantibodies
Vitamin B12 deficiency
Menstrual blood loss
5-12. A 75-year-old male develops a cough that produces blood-tinged
sputum. He has a fever of 104°F. Gram-positive cocci in clusters are found
in a sputum smear. A chest x-ray shows increased density in the right
upper lobe. Of the following penicillins, which is most likely to be ineffective?
a.
b.
c.
d.
e.
Oxacillin
Cloxacillin
Ticarcillin
Nafcillin
Dicloxacillin
98
Clinical Vignettes for the USMLE Step 1
5-13. A 28-year-old woman comes into the emergency room exhibiting
dyspnea and mild cyanosis, but no signs of trauma. Her chest x-ray is
shown below. The most obvious abnormal finding in the inspiratory posteroanterior chest x-ray of this patient (viewed in the anatomic position) is a
a.
b.
c.
d.
e.
Bilateral expansion of the pleural cavities above the first rib
Grossly enlarged heart
Left pneumothorax (collapsed lung)
Paralysis of the left hemidiaphragm
Right hemothorax (blood in the pleural cavity)
5-14. A 34-year-old patient with chronic schizophrenia is hospitalized on
a chronic ward of a psychiatric hospital and is on an appropriate dose of
antipsychotic medication. He frequently shouts in the halls, disrupting
activities and annoying the other patients. The best behavioral strategy for
this patient would be
a.
b.
c.
d.
e.
Psychological counseling
Contingency management
Stimulus control
Role-play therapy
Modeling
Block 5
Questions
99
5-15. A patient is confused and displays localized jerks in his right hand,
which progress to jerks of the entire arm with a brief loss of consciousness.
This disorder can best be characterized as a
a.
b.
c.
d.
e.
Generalized seizure
Absence seizure
Simple partial seizure
Complex partial seizure
Petit mal seizure
5-16. A 2-year-old child was admitted to the hospital with acute meningitis.
The Gram stain revealed Gram-positive short rods, and the mother indicated
that the child had received “all” of the meningitis vaccinations. What is the
most likely cause of the disease?
a.
b.
c.
d.
e.
N. meningitidis, group A
N. meningitidis, group C
Listeria
S. pneumoniae
H. influenzae
5-17. A 5-year-old boy presents with clumsiness, a waddling gait, and difficulty climbing steps. Physical examination reveals that this boy uses his
arms and shoulder muscles to rise from the floor or a chair. Additionally,
his calves appear to be somewhat larger than normal. This boy’s physical
findings are most consistent with a diagnosis of
a.
b.
c.
d.
e.
Inclusion body myositis
Werdnig-Hoffmann disease
Dermatomyositis
Duchenne’s muscular dystrophy
Myotonic dystrophy
100
Clinical Vignettes for the USMLE Step 1
5-18. A child is referred for evaluation because of low muscle tone and
developmental delay. Shortly after delivery the child was a poor feeder and
had to be fed by tube. In the second year, the child began to eat voraciously
and became obese. He has a slightly unusual face with almond-shaped eyes
and downturned corners of the mouth. The hands, feet, and penis are
small, and the scrotum is poorly formed. The diagnostic category and laboratory test to be considered for this child are
a.
b.
c.
d.
e.
Sequence, serum testosterone
Single birth defect, serum testosterone
Deformation, karyotype
Syndrome, karyotype
Disruption, karyotype
5-19. A 70-year-old man complains of a sensation of food sticking in his
lower chest area. This happens when he eats either liquids or solids. He
also has a slight weight loss. The most likely diagnosis is
a.
b.
c.
d.
e.
Achalasia
Esophageal spasm
Hypertensive LES
Hiatal hernia with GERD
Barrett’s esophagus
5-20. A 16-year-old male treated for acute lymphocytic leukemia develops
severe lumbar and abdominal pain. His serum amylase is markedly elevated. Which of the following agents most likely caused these findings?
a.
b.
c.
d.
e.
6-MP
Asparaginase
Doxorubicin
Methotrexate
Vincristine
Block 5
Questions
101
5-21. A middle-aged woman has developed a pattern of compulsive eating
of snack foods and fast foods from restaurant chains, in response to tension
and anxiety. Over several years she has gained 80 lbs from a normal weight
for her height. This pathologic eating behavior is most likely to predispose
the patient to
a.
b.
c.
d.
e.
Diabetes mellitus
Atherosclerosis
Hypertension
Sleep apnea
Gallstones
5-22. A 40-year-old man with occasional dysphagia and who otherwise
feels well undergoes esophageal motility studies that show an LES amplitude of approximately 60 mmHg. The esophagus relaxes completely when
he swallows. The most likely diagnosis is
a.
b.
c.
d.
e.
GERD (gastroesophageal reflux disease)
Achalasia
Hypertensive LES
Barrett’s esophagus
Esophageal spasm
5-23. A newborn with ambiguous genitalia and a 46,XY karyotype develops vomiting, low serum sodium concentration, and high serum potassium. Which of the following proteins is most likely to be abnormal?
a.
b.
c.
d.
e.
21-hydroxylase
An ovarian enzyme
5α-reductase
An androgen receptor
A testicular enzyme
102
Clinical Vignettes for the USMLE Step 1
Questions 5-24 through 5-25
Herb, a 62-year-old man who has smoked two packs of cigarettes per
day for 35 years, was suffering from a chronic cough that was attributed to
smoking habit by his physician. One day, Herb noticed that his right eyelid
drooped slightly and that his right pupil was smaller than the left. He also
noticed that the inner side of his right hand was numb and that he had
begun to drop things from his right hand. He had no other symptoms.
Herb consulted his physician who directed him to a neurologist.
The neurologist noted that although the right pupil was smaller than
the left, it was still reactive to light. Although Herb’s right eyelid drooped
slightly, he could close his eyes tightly when asked to do so. The neurologist noted that Herb did not sweat on the right side of his face. He was
unable to feel a pinprick on the inner surface of his right hand, and his
right triceps and hand muscles were weak.
5-24. Where in the nervous system has damage occurred?
a.
b.
c.
d.
Left oculomotor nerve
Right oculomotor nerve
Edinger-Westphal nucleus
Sympathetic fibers coursing from the hypothalamus to the intermediolateral
cell column
e. Parasympathetic fibers coursing from the Edinger-Westphal nucleus
5-25. Herb’s small pupil is due to
a.
b.
c.
d.
e.
Unopposed action of the muscles with parasympathetic innervation
Unopposed action of the muscles with sympathetic innervation
Both sympathetic and parasympathetic damage
A lesion in the nucleus of the third nerve
A lesion distal branches of the trochlear nerve
Block 5
Questions
103
YOU SHOULD HAVE COMPLETED APPROXIMATELY
25 QUESTIONS AND HAVE 30 MINUTES REMAINING.
5-26. A 50-year-old patient has just lost his wife of 30 years and is suffering
from the acute stress of bereavement. Without medical intervention such as
supervision of factors affecting his mental and physical health, recommendation of support groups, and the scheduling of regular visits over the next six
months, the patient will be subject to an increased mortality risk of
a.
b.
c.
d.
e.
10%
20%
30%
40%
50%
5-27. A teenager who works in a dog kennel after school has had a skin
rash, eosinophilia, and an enlarged liver and spleen for 2 years. The most
likely cause of this infection is
a.
b.
c.
d.
e.
Trichinosis
Schistosomiasis
Toxoplasmosis
Visceral larva migrans
Giardiasis
104
Clinical Vignettes for the USMLE Step 1
5-28. An Asian child has severe anemia with prominence of the forehead
(frontal bossing) and cheeks. The red cell hemoglobin concentration is dramatically decreased, and it contains only β-globin chains with virtual deficiency of α-globin chains. Which of the following mechanisms is a
potential explanation?
a.
b.
c.
d.
e.
A transcription factor regulating the α-globin gene is mutated
A regulatory sequence element has been mutated adjacent to an α-globin gene
A transcription factor regulating the β-globin gene is mutated
A transcription factor regulating the α-globin and β-globin genes is deficient
A deletion has occurred surrounding an α-globin gene
5-29. A 23-year-old HIV-positive male presents with a cough and increasing shortness of breath. A histologic section from a transbronchial biopsy
stained with Gomori’s methenamine-silver stain is shown in the photomicrograph below. What is the correct diagnosis?
a.
b.
c.
d.
e.
Pseudomonas pneumonia
Aspergillus pneumonia
Pneumocystis carinii pneumonia
Cytomegalovirus pneumonia
Influenza pneumonia
Block 5
Questions
105
5-30. An enterococcus (E. faecium) was isolated from a urine specimen
(100,000 cfu/mL). Treatment of the patient with ampicillin and gentamicin
failed. The most clinically appropriate action is
a. Do no further clinical workup
b. Suggest to the laboratory that low colony counts may reflect infection
c. Determine if fluorescent microscopy is available for the diagnosis of actinomycosis
d. Consider vancomycin as an alternative drug
e. Suggest a repeat antibiotic susceptibility test
5-31. A 16-year-old male treated for bronchial asthma develops skeletal
muscle tremors. Which of the following agents may be responsible for this
finding?
a.
b.
c.
d.
e.
Ipratropium
Zileuton
Beclomethasone
Cromolyn
Salmeterol
5-32. During a routine physical examination, a 42-year-old female is
found to have an elevated blood pressure of 150/100 mmHg. Workup
reveals a small left kidney and a normal-sized right kidney. Laboratory
examination reveals elevated serum renin levels. Further workup reveals
that renal vein renin levels are increased on the left but decreased on the
right. This patient’s hypertension is most likely the result of
a.
b.
c.
d.
e.
Atherosclerotic narrowing of the left renal artery
Atherosclerotic narrowing of the right renal artery
Fibromuscular hyperplasia of the left renal artery
Fibromuscular hyperplasia of the right renal artery
Hyaline arteriolosclerosis
106
Clinical Vignettes for the USMLE Step 1
Questions 5-33 through 5-34
An individual is admitted to the emergency room and is diagnosed as
having cortical damage and resultant neuronal degeneration due to an
ischemic insult. The neurologist concluded that the brain damage involved
neurotoxicity of those cells.
5-33. The neurotransmitter change associated with neurotoxicity in this
case is believed to involve
a.
b.
c.
d.
e.
Extracellular accumulation of norepinephrine
Extracellular accumulation of ACh
Extracellular accumulation of glutamate
Extracellular loss of serotonin
Extracellular loss of GABA
5-34. The likely mechanism underlying neurotoxicity as a result of
ischemia involves
a.
b.
c.
d.
e.
Entry of Ca2+ into the cell
Reduction of extracellular chloride
Delayed removal of norepinephrine from the synapse
Hypersensitivity of the postsynaptic membrane to GABA
Failure of degradation of ACh
5-35. A 28-year-old woman presents complaining of infertility. She had a
healthy child 3 years ago and has been trying to get pregnant with the
child’s father for the last 18 months. She does not have dysmenorrhea. Her
menses occur regularly, but these show significantly less flow compared
with before her pregnancy. She recalls having a curettage performed to
remove placental remnants. What is the most likely diagnosis?
a.
b.
c.
d.
e.
Ovarian failure
Hypothyroidism
Asherman’s syndrome
Endometriosis
Prolactinoma
Block 5
Questions
107
5-36. A 5-year-old Egyptian boy receives a sulfonamide antibiotic as prophylaxis for recurrent urinary tract infections. Although he was previously
healthy and well-nourished, he becomes progressively ill and presents to
your office with pallor and irritability. A blood count shows that he is
severely anemic with jaundice due to hemolysis of red blood cells. Which
of the following would be the simplest test for diagnosis?
a.
b.
c.
d.
Northern blotting of red blood cell mRNA
Enzyme assay of red blood cell hemolysate
Western blotting of red blood cell hemolysates
Amplification of red blood cell DNA and hybridization with allele-specific
oligonucleotides (PCR-ASOs)
e. Southern blot analysis for gene deletions
5-37. A 45-year-old male post–myocardial infarction (post-MI) for one
week is being treated with intravenous (IV) heparin. Stool guaiac on admission was negative, but is now 4+, and he has had an episode of hematemesis. The heparin is discontinued, and a drug is given to counteract the
bleeding. What drug was given?
a.
b.
c.
d.
e.
Aminocaproic acid
Dipyridamole
Factor IX
Protamine
Vitamin K
108
Clinical Vignettes for the USMLE Step 1
5-38. Your patient is a 30-year-old male who lives in a group home. He
was playing with a pencil and, during a fall, accidentally drove the pencil
deeply into a nostril. The pencil was angled toward the midline structure
indicated by the arrow in this midsagittal MRI. The pencil was driven
toward the
(indicated by the arrow).
through the
a.
b.
c.
d.
e.
Nasal cavity and nasopharynx, toward the pharyngeal tonsil
Nasal cavity and sphenoidal sinus, toward the pituitary
Nasal cavity and sphenoidal sinus, toward the internal carotid artery
Nasal cavity and ethmoidal air cells, toward the circle of Willis
Nasal cavity, toward the basilar artery
Block 5
Questions
109
5-39. A patient is being treated by a behavioral technique for a phobia that
is precipitated by being in a crowded situation. The patient is taught muscular relaxation; then, while using the relaxation to inhibit the anxiety, the
patient is told to imagine a series of progressively more severe anxietyprovoking situations. This technique is called
a.
b.
c.
d.
e.
Modeling
Stress inoculation
Systematic desensitization
Conditioned compensatory response
Contingency conditioning
5-40. A 6-year-old female is being evaluated for recurrent episodes of
lightheadedness and sweating due to hypoglycemia. These symptoms are
not improved by subcutaneous injection of epinephrine. Physical examination reveals an enlarged liver and a single subcutaneous xanthoma. An
abdominal CT scan reveals enlargement of the liver along with bilateral
enlargement of the kidneys. Laboratory examination reveals increased
serum uric acid and cholesterol with decreased serum glucose levels. Following oral administration of fructose, there is no increase in blood glucose
levels. A liver biopsy specimen reveals increased amounts of glycogen in
hepatocytes, which also have decreased levels of glucose-6-phosphatase.
What is the correct diagnosis?
a.
b.
c.
d.
e.
Andersen’s syndrome (type IV glycogen storage disease)
Cori’s disease (type III glycogen storage disease)
McArdle’s syndrome (type V glycogen storage disease)
Pompe’s disease (type II glycogen storage disease)
von Gierke’s disease (type I glycogen storage disease)
5-41. A 16-year-old boy takes the drug of abuse, phencyclidine (PCP).
The deleterious effects of the drug are due in part to
a.
b.
c.
d.
e.
Blockade of NMDA receptors
Blockade of AMPA receptors
Blockade of cholinergic receptors
Blockade of GABAA receptors
Blockade of GABAB receptors
110
Clinical Vignettes for the USMLE Step 1
5-42. Your new patient is a 45-year-old, recently divorced woman. She
has just told you that her 25-year-old son returned home three days ago
with AIDS, and that she has experienced severe chest pains when she
thinks about it. She starts to tell you about some other disturbing symptoms, begins to cry, and looks away. Of the following, which would be the
most appropriate immediate response to facilitate the interview?
a.
b.
c.
d.
e.
Silence
“I know how you feel”
“Don’t worry, it’ll be OK”
“Why are you so upset? You know you can tell me anything”
“Are you thinking that you may have AIDS?”
5-43. A 45-year-old man complains of frequent “heartburn” and a mild
chronic cough. On examination, he has gastroesophageal reflux disease
(GERD). In addition to prescribing medications, which one of the following dietary recommendations would you make?
a. Avoid high-protein meals because they would increase lower esophageal
sphincter (LES) pressure
b. Avoid fats, chocolates, and alcohol because they would decrease LES pressure
c. Eat high-carbohydrate food to increase overall GI motility
d. Eat high-protein meals to decrease LES pressure
e. Avoid concentrated carbohydrates to decrease dopamine secretion
5-44. An elderly woman visits the hospital emergency room with the recent
onset of grotesque swelling of the right arm, neck, and face. Her right jugular vein is visibly engorged and her right brachial pulse is diminished. On
the basis of these signs, her chest x-rays might show
a.
b.
c.
d.
e.
A left cervical rib
A mass in the upper lobe of the right lung
Aneurysm of the aortic arch
Right pneumothorax
Thoracic duct blockage in the posterior mediastinum
Block 5
Questions
111
5-45. A 77-year-old man complains to you of an annoying buzzing sound
in his right ear that bothers him mostly at night. This is classified as
a.
b.
c.
d.
e.
Conductive deafness
Sensorineural deafness
Central deafness
Tinnitus
Presbycusis
5-46. Jill and Tom have been neighbors and close friends their whole lives.
They are both 13 years old and are in the same eighth grade class. Jill has
begun to notice and talk about a few of the ninth grade boys and she
spends less time with Tom. Tom is upset and feels hurt and inferior. The
most likely cause of this situation is that
a.
b.
c.
d.
Other boys are beginning to notice Jill
Jill’s girlfriends are beginning to spend more time with new friends
Tom’s physical development is slower than Jill’s
Jill’s cognitive and social development has made her more interested in her girlfriends
e. Tom’s physical development has made him show more interest in competitive
sports
5-47. A 6-year-old girl presents to the clinic with scaly patches on the
scalp. Primary smears and culture of the skin and hair were negative. A few
weeks later, she returned and was found to have inflammatory lesions. The
hair fluoresced under Wood’s light and primary smears of skin and hair
contained septate hyphae. On speaking with the parents, it was discovered
that there were several pets in the household. Which of the following is the
most likely agent?
a.
b.
c.
d.
e.
Microsporum audouinii
Microsporum canis
Trichophyton tonsurans
Trichophyton rubrum
Epidermophyton floccosum
112
Clinical Vignettes for the USMLE Step 1
5-48. A 54-year-old male presents with several problems involving his
face and pain in his shoulder. He states that he has smoked 2 packs of cigarettes a day for almost 40 years. Physical examination reveals ptosis of his
left upper eyelid, constriction of his left pupil, and lack of sweating
(anhidrosis) on the left side of his face. No other neurologic abnormalities
are found. This individual most likely has
a.
b.
c.
d.
e.
A bronchioloalveolar carcinoma involving the left upper lobe
A small cell carcinoma involving the hilum of his left lung
A squamous cell carcinoma involving the left mainstem bronchus
An adenocarcinoma involving the apex of his left lung
An endobronchial carcinoid tumor involving the right mainstem bronchus
5-49. An 18-year-old male high school baseball player gets hit in the head
with a fastball in the temporal area. He does not lose consciousness, but
afterward develops a slight headache. He is not taken to the emergency
room. By evening he develops severe headache with vomiting and confusion. At that time he is taken to the emergency room, where, after being
examined by a neurosurgeon, he is taken to the operating room for immediate surgery for an epidural hematoma. Which one of the following is
most likely present in this individual?
a.
b.
c.
d.
e.
Transection of a branch of the middle meningeal artery
Bleeding from torn bridging veins
Rupture of a preexisting berry aneurysm
Rupture of an arteriovenous malformation
Cortical bleeding occurring opposite the point of a traumatic injury
5-50. After a mild hemorrhage, compensatory responses initiated by the
baroreceptor reflex keeps blood pressure at or close to its normal value.
Which one of the following values is less after compensation for the hemorrhage than it was before the hemorrhage?
a.
b.
c.
d.
e.
Venous compliance
Heart rate
Ventricular contractility
Total peripheral resistance
Coronary blood flow
BLOCK 6
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
BLOCK 6
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Questions
6-1. A college student received an injury as a result of being tackled in a
football game. After the game, the student was treated at a local hospital
and was found to be unable to abduct and rotate the left arm at the shoulder, flex the elbow, and extend the wrist of the left side. Upon further
examination, testing revealed depression of the biceps reflex of this limb,
but the reflex activity involving the other limbs was normal. The most
likely site of the injury is
a.
b.
c.
d.
e.
Precentral gyrus
Basilar pons
Ventral horn cells at C1
Nerve roots of C5-C6
Triceps muscle
115
116
Clinical Vignettes for the USMLE Step 1
6-2. An elderly, somewhat obese man is brought to the emergency room
complaining of sudden spontaneous flailing movements of his right arm
and leg. The arm movements particularly were most severe proximally. No
other neurologic deficits were noted. The patient had most likely suffered a
hemorrhage in
a.
b.
c.
d.
e.
The cerebellum
The ventral horn of the spinal cord
The hypothalamus
Primary sensory cortex
The subthalamic nucleus
6-3. A 32-year-old man is admitted with a bleeding ulcer. This is his fifth
episode of bleeding from gastric ulcers and he also has moderate diarrhea.
Each time, his ulcers have been difficult to resolve. Which neoplastic lesion
is most likely to be found in this man?
a.
b.
c.
d.
e.
Small cell carcinoma of the lung
Gastric adenocarcinoma
Small intestinal carcinoid
Prostate adenocarcinoma
Gastrinoma
6-4. A 2-day-old neonate becomes lethargic and uninterested in breastfeeding. Physical examination reveals tachypnea (rapid breathing) with a
normal heartbeat and breath sounds. Initial blood chemistry values include
normal glucose, sodium, potassium, chloride, and bicarbonate (HCO3−)
levels; initial blood gas values reveal a pH of 7.53, partial pressure of oxygen (PO2) normal at 103 mmHg, and partial pressure of carbon dioxide
(PCO2) decreased at 27 mmHg. Which of the following treatment strategies
is indicated?
a.
b.
c.
d.
e.
Administer alkali to treat metabolic acidosis
Administer alkali to treat respiratory acidosis
Decrease the respiratory rate to treat metabolic acidosis
Decrease the respiratory rate to treat respiratory alkalosis
Administer acid to treat metabolic alkalosis
Block 6
Questions
117
6-5. The first child of a couple has trisomy 21 (not the result of
mosaicism), and they come to you wanting to know the risk of having
another child with Down’s syndrome. The mother’s age is 23, and the
father’s age is 25. Both appear normal and neither have had any unusual
diseases. You analyze their karyotypes and find that the father’s karyotype
is normal, but the mother has a Robertsonian translocation involving chromosome 21 (21q21q). Which one of the listed percentages is the best estimate of the chance that the next living child of this couple will have Down’s
syndrome?
a.
b.
c.
d.
e.
0%
15%
33%
50%
100%
6-6. Lethargy, malaise, and fatigue are observed in a patient 2 weeks after
eating raw hamburger at a restaurant. The most likely infectious cause is
a.
b.
c.
d.
e.
Toxoplasma
Cytomegalovirus
E. coli
Salmonella
Clostridium
6-7. A man presents with a wide-based, ataxic gait during his attempts at
walking. He also is unsteady and sways when standing and displays a tendency to fall backward or to either side in a drunken manner. A lesion is
most likely located in the
a.
b.
c.
d.
e.
Hemispheres of the posterior cerebellar lobe
Anterior limb of the internal capsule
Dentate nucleus
Anterior lobe of the cerebellum
Flocculonodular lobe of the cerebellum
118
Clinical Vignettes for the USMLE Step 1
6-8. A 55-year-old postmenopausal female develops weakness, polyuria,
and polydipsia. Nephrocalcinosis is detected by a computed tomography
(CT) scan. Her serum creatinine is elevated. Which of the following agents
may have caused these adverse effects?
a.
b.
c.
d.
e.
Estrogens
Prednisone
PTU
Etidronate
Vitamin D
6-9. A patient with jaundice complains of RUQ pain. Liver function tests
show a bilirubin of 3.0 mg/dL, alkaline phosphatase about four times normal and both AST and ALT increased about 50% above normal. The best
imaging test to order first in evaluating this patient would be
a.
b.
c.
d.
e.
Ultrasound
Abdominal CT scan
Abdominal MRI
Barium swallow
KUB (flat-plate x-ray of the abdomen)
6-10. A patient with symptoms of urinary tract infection had a culture
taken, which grew 5 × 103 E. coli. The laboratory reported it as “insignificant.” The most clinically appropriate action is
a. Do no further clinical workup
b. Suggest to the laboratory that low colony counts may reflect infection
c. Determine if fluorescent microscopy is available for the diagnosis of actinomycosis
d. Consider vancomycin as an alternative drug
e. Suggest a repeat antibiotic susceptibility test
Block 6
Questions
119
6-11. A 4-year-old girl presents in the clinic with megaloblastic anemia
and failure to thrive. Blood chemistries reveal orotic aciduria. Enzyme measurements of white blood cells reveal a deficiency of the pyrimidine biosynthesis enzyme orotate phosphoribosyltransferase and abnormally high
activity of the enzyme aspartate transcarbamoylase. Which one of the following treatments will reverse all symptoms if carried out chronically?
a.
b.
c.
d.
e.
Blood transfusion
White blood cell transfusion
Dietary supplements of phosphoribosylpyrophosphate (PRPP)
Oral thymidine
Oral uridine
6-12. A lumbar puncture is performed on a patient with headaches, photophobia, clouding of consciousness, and neck stiffness. If these symptoms
are the result of bacterial infection of the meninges, then what would
examination of the cerebrospinal fluid (CSF) most likely reveal?
a.
b.
c.
d.
e.
Pressure
Increased
Increased
Increased
Decreased
Increased
Gross
Appearance
Cloudy
Clear
Clear
Clear
Clear
Protein
Increased
Increased
Increased
Decreased
Increased
Glucose
Decreased
Normal
Normal
Normal
Normal
Inflammation
Neutrophils
Lymphocytes
Mononuclear cells
Lymphocytes
Mixed
120
Clinical Vignettes for the USMLE Step 1
Questions 6-13 through 6-14
A 67-year-old woman slipped on a throw-rug and fell with her right
arm extended in an attempt to ease the impact of the fall. She experienced
immediate severe pain in the region of the right collar bone and in the right
wrist. Painful movement of the right arm was minimized by holding the
arm close to the body and by supporting the elbow with the left hand.
6-13. There is marked tenderness and some swelling in the region of the
clavicle about one-third of the distance from the sternum. The examiner
can feel the projecting edges of the clavicular fragments. The radiograph
confirms the fracture and shows elevation of the proximal fragment with
depression and subluxation (underriding) of the distal fragment. Traction
by which of the following muscles causes subluxation (the distal fragment
underrides the proximal fragment)?
a.
b.
c.
d.
e.
Deltoid muscle
Pectoralis major muscle
Pectoralis minor muscle
Sternomastoid muscle
Trapezius muscle
6-14. Internal bleeding can be a complication if the subluxed bone fragment tears a vessel and punctures the pleura. Which of the following vascular structures is particularly vulnerable in a clavicular fracture?
a.
b.
c.
d.
e.
Axillary artery
Brachiocephalic artery
Lateral thoracic artery
Subclavian artery
Thoracoacromial trunk
Block 6
Questions
121
6-15. A 21-year-old man was bitten by a tick in Oregon. Two years later,
during the course of routine screening for an unknown ailment, a screening Lyme disease test was performed, which was negative. A Western blot
strip (IgG) showed the following pattern:
Which of the following is the correct interpretation of the test?
a.
b.
c.
d.
e.
The patient has acute Lyme disease
The patient has chronic Lyme disease
The pattern may represent nonspecific reactivity
The screening test should be repeated
The patient should be tested for HIV on the basis of the Western blot
6-16. A 24-year-old female presents after having several “attacks” that last
for about 24 h. She states that during these attacks she develops nausea,
vomiting, vertigo, and ringing in her ears. Physical examination reveals a
sensorineural hearing loss. The pathology of her condition involves
a.
b.
c.
d.
Acute suppurative inflammation
Dilation of the cochlear duct and saccule
A cyst of the middle ear filled with keratin
A tumor of the middle ear composed of lobules of cells in a highly vascular
stroma
e. New bone formation around the stapes and the oval window
122
Clinical Vignettes for the USMLE Step 1
6-17. A 27-year-old female is diagnosed with hypercortisolism. To determine whether cortisol production is independent of the pituitary gland,
you decide to suppress ACTH production by giving a high-potency glucocorticoid. Which glucocorticoid is the best for this indication?
a.
b.
c.
d.
e.
Triamcinolone
Prednisone
Hydrocortisone
Dexamethasone
Methylprednisolone
6-18. A patient with a peptic ulcer was admitted to the hospital and a gastric biopsy was performed. The tissue was cultured on chocolate agar incubated in a microaerophilic environment at 37°C for 5 to 7 days. At 5 days
of incubation, colonies appeared on the plate and were curved, Gramnegative rods, oxidase-positive. The most likely identity of this organism is
a.
b.
c.
d.
e.
Campylobacter jejuni
Vibrio parahaemolyticus
Haemophilus influenzae
Helicobacter pylori
Campylobacter fetus
6-19. A 62-year-old male alcoholic is brought into the emergency room
acting very confused. Physical examination reveals a thin and emaciated
male who has problems with memory, ataxia, and paralysis of his extraocular muscles. Extensive workup reveals atrophy and small hemorrhages in
the periventricular region of his brain and around the mamillary bodies.
These signs and symptoms are most consistent with a deficiency of
a.
b.
c.
d.
e.
Biotin
Riboflavin
Selenium
Pyridoxine
Thiamine
Block 6
Questions
123
6-20. A 45-year-old female being treated for a chronic UTI develops acute
alcohol intolerance. Which of the following agents could have caused this
intolerance?
a.
b.
c.
d.
e.
Cefoperazone
Amoxicillin
Sulfamethoxazole-trimethoprim
Norfloxacin
Tetracycline
6-21. A man known to be an alcoholic for at least 15 years presents with
fever, elevated serum bilirubin, elevated WBC count, and an AST/ALT ratio
greater than 2. A liver biopsy shows Mallory bodies, WBCs, and degenerating cells. You should tell this patient that the biopsy findings are
a. Consistent with cirrhosis
b. Essentially normal
c. Consistent with alcoholic hepatitis that may revert to normal if he stops drinking alcohol
d. Consistent with alcoholic hepatitis that will progress to cirrhosis
e. Not interpretable because of the presence of degenerating cells and it will need
to be repeated
6-22. You have been asked to evaluate a 62-year-old man for a possible
early dementia. The initial interview with the patient is not remarkable. The
most common presenting feature of Alzheimer’s disease that you should
now focus your diagnostic evaluation on is
a.
b.
c.
d.
e.
Change in personality
Loss of memory
Difficulty in learning new information
Impairment of orientation to time
Loss of intellectual skills
6-23. A 60-year-old female treated for breast cancer develops leukopenia
and severe stomatitis and oral ulcerations. Which of the following agents
most likely caused these findings?
a.
b.
c.
d.
e.
5-FU
Paclitaxel
Cyclophosphamide
Tamoxifen
Carboplatin
124
Clinical Vignettes for the USMLE Step 1
6-24. When a patient is asked to follow an object when it is placed in the
right side of his visual field, he is unable to move his right eye either up or
down. The lesion is most likely situated in the
a.
b.
c.
d.
e.
Medulla
Basilar aspect of the pons
Pontine tegmentum
Midbrain
Cerebellum
6-25. A man with chills, fever, and headache is thought to have “atypical”
pneumonia. History reveals that he raises chickens and that approximately
2 weeks ago he lost a large number of them to an undiagnosed disease. The
most likely diagnosis of this man’s condition is
a.
b.
c.
d.
e.
Anthrax
Q fever
Relapsing fever
Leptospirosis
Ornithosis (psittacosis)
Block 6
Questions
125
YOU SHOULD HAVE COMPLETED APPROXIMATELY
25 QUESTIONS AND HAVE 30 MINUTES REMAINING.
6-26. A patient is found to have internal (medially directed) strabismus of
the left eye, paralysis of the muscles of facial expression on the left side,
hyperacusis (louder perception of sounds) of the left ear, and loss of taste
from the anterior two-thirds of the tongue on the left. The mouth is somewhat drier than normal. In addition, in the left eye there is a lack of tearing, and a blink reflex cannot be elicited from the stimulation of either the
right or the left cornea. There is accompanying upper motor neuron paralysis of the right side of the body. Internal strabismus (deviation of the eye
medially) results from paralysis of which of the following cranial nerves?
a.
b.
c.
d.
e.
Cranial nerve II
Cranial nerve III
Cranial nerve IV
Cranial nerve V
Cranial nerve VI
126
Clinical Vignettes for the USMLE Step 1
6-27. A 44-year-old obese male has a significantly high level of plasma
triglycerides. Following treatment with one of the following agents, his
plasma triglyceride levels decrease to almost normal. Which agent did he
receive?
a.
b.
c.
d.
Neomycin
Lovastatin
Cholestyramine
Gemfibrozil
6-28. A 55-year-old man begins to be emotionally labile, tense, hyperexcitable. He has recently had difficulty with his job. He has lost 20 lbs in
weight. He is distractable, has a short attention span, and has impaired
recent memory. Your initial workup reveals a fine tremor of the hands, and
laboratory work suggests an endocrine abnormality. What is the most likely
diagnosis?
a.
b.
c.
d.
e.
Hypoparathyroidism
Hyperthyroidism
Hyperparathyroidism
Hypothyroidism
Addison’s disease
6-29. A 65-year-old man is diagnosed with a form of a peripheral neuropathy. This individual will likely display
a.
b.
c.
d.
e.
A loss in motor function, but sensory functions will remain largely intact
A reduction in conduction velocity of the affected nerve
An increase in the number of Ranvier’s nodes
Degeneration of myelin but the axon will typically remain intact
Signs of an upper motor neuron (UMN) paralysis
6-30. A patient in heart failure improves markedly after using a drug that
increases the inotropic state of her heart. Which one of the following
changes is primarily responsible for the improvement in her condition?
a.
b.
c.
d.
e.
A reduction in heart rate
A reduction in heart size
An increase in end-diastolic pressure
An increase in wall thickness
An increase in cardiac excitability
Block 6
Questions
127
6-31. A young girl has had repeated infections with Candida albicans and
respiratory viruses since the time she was 3 months old. As part of the clinical evaluation of her immune status, her responses to routine immunization procedures should be tested. In this evaluation, the use of which of the
following vaccines is contraindicated?
a.
b.
c.
d.
e.
Diphtheria toxoid
Bordetella pertussis vaccine
Tetanus toxoid
BCG
Inactivated polio
6-32. A 41-year-old female is seen in the psychiatric clinic for a follow-up
appointment. She has been taking an antidepressant for three weeks with
some improvement in mood. However, she complains of drowsiness, palpitations, dry mouth, and feeling faint on standing. Which antidepressant
is she taking?
a.
b.
c.
d.
e.
Amitriptyline
Trazodone
Fluoxetine
Venlafaxine
Bupropion
6-33. A 38-year-old woman with rheumatoid arthritis develops worse
joint pain and also pain and paresthesias in scattered locations in both
arms and both legs. Her sedimentation rate increases significantly and you
diagnose vasculitis causing
a.
b.
c.
d.
e.
Mononeuropathy
Brown-Séquard’s syndrome
Polyneuropathy
Mononeuropathy multiplex
Radiculopathy
128
Clinical Vignettes for the USMLE Step 1
6-34. A sputum sample was brought to the laboratory for analysis. Gram
stain revealed the following: rare epithelial cells, 8 to 10 polymorphonuclear leukocytes per high-power field, and pleomorphic Gram-negative
rods. As the laboratory consultant, which of the following interpretations
should you make?
a.
b.
c.
d.
e.
The sputum specimen is too contaminated by saliva to be useful
There is no evidence of an inflammatory response
The patient has pneumococcal pneumonia
The patient has Vincent’s disease
The appearance of the sputum is suggestive of Haemophilus pneumonia
6-35. A 55-year-old female with painful chronic diarrhea, multiple recurrent duodenal ulcers, and increased basal gastric acid output is most likely
to have
a.
b.
c.
d.
e.
A gastrin-secreting tumor of the pancreas
A serotonin-secreting tumor of the ileum
A somatostatin-secreting tumor of the duodenum
An epinephrine-secreting tumor of the adrenal medulla
An erythropoietin-secreting tumor of the liver
6-36. A middle-aged man presents with congestive heart failure with elevated liver enzymes. His skin has a grayish pigmentation. The levels of liver
enzymes are higher than those usually seen in congestive heart failure, suggesting an inflammatory process (hepatitis) with scarring (cirrhosis) of the
liver. A liver biopsy discloses a marked increase in iron storage. In humans,
molecular iron (Fe) is
a.
b.
c.
d.
e.
Stored primarily in the spleen
Stored in combination with ferritin
Excreted in the urine as Fe++
Absorbed in the intestine by albumin
Absorbed in the ferric (Fe+++) form
Block 6
Questions
129
6-37. A 41-year-old man comes to your office with his wife because she
has been unable to conceive with him. He is married for the first time. His
wife has two children by her previous marriage. The patient is well with
no risk factors for heart disease. As a child, he had the usual communicable diseases, including chickenpox and mumps, and as an adult he
received the recommended schedule of immunizations. The likely site of
his infertility is
a.
b.
c.
d.
Pretesticular
Testicular
Posttesticular
Idiopathic
6-38. A 65-year-old male with a pneumonia has a sputum culture that is
positive for a staphylococcal strain that is β-lactamase-positive. Which is
the best choice of penicillin therapy in this patient?
a.
b.
c.
d.
e.
Ampicillin
Oxacillin
Ticarcillin
Penicillin G
Carbenicillin
130
Clinical Vignettes for the USMLE Step 1
Questions 6-39 through 6-40
After an individual is admitted to the hospital, it is determined that he
displays a variable weakness of cranial nerve and limb muscles but shows
no clinical signs of denervation from tests, which include electromyogram
(EMG) recordings. This disorder was partially reversed by the administration of drugs that inhibit acetylcholinesterase.
6-39. The individual is likely to be suffering from
a.
b.
c.
d.
e.
Multiple sclerosis (MS)
Amyotrophic lateral sclerosis (ALS)
Myasthenia gravis
Combined system disease
Muscular dystrophy (MD)
6-40. The likely basis for this disorder is the result of
a.
b.
c.
d.
e.
The production of excessive quantities of acetylcholine (ACh)
The production of antibodies that act against nicotinic ACh receptors
A minor stroke involving the motor strip of the cerebral cortex
A vitamin B deficiency
Viral encephalitis
6-41. A family in which several individuals have arthritis and detached
retina is diagnosed with Stickler syndrome. The locus for Stickler syndrome has been mapped near that for type II collagen on chromosome 12,
and mutations in the COL2A1 gene have been described in Stickler syndrome. The family became interested in molecular diagnosis to distinguish
normal from mildly affected individuals. Which of the results below would
be expected in an individual with a promoter mutation at one COL2A1
gene locus?
a. Western blotting detects no type II collagen chains
b. Southern blotting using intronic restriction sites yields normal restriction fragment sizes
c. Reverse transcriptase–polymerase chain reaction (RT-PCR) detects one-half
normal amounts of COL2A1 mRNA in affected individuals
d. Fluorescent in situ hybridization (FISH) analysis using a COL2A1 probe detects
signals on only one chromosome 12
e. DNA sequencing reveals a single nucleotide difference between homologous
COL2A1 exons
Block 6
Questions
131
6-42. A 53-year-old banker develops paralysis on the right side of the face,
which produces an expressionless and drooping appearance. He is unable
to close the right eye and also has difficulty chewing and drinking. Examination shows loss of blink reflex in the right eye to stimulation of either
right or left conjunctiva. Lacrimation appears normal on the right side, but
salivation is diminished and taste is absent on the anterior right side of the
tongue. There is no complaint of hyperacusis. Audition and balance appear
to be normal. The lesion is located
a. In the brain and involves the nucleus of the facial nerve and superior salivatory
nucleus
b. Within the internal auditory meatus
c. At the geniculate ganglion
d. In the facial canal just distal to the genu of the facial nerve
e. Just proximal to the stylomastoid foramen
6-43. A 21-year-old female presents because her urine has turned a brown
color. She states that about 2 months ago her urine turned brown 2 days
after a cold and stayed brown for about 3 days. At the current time a urinalysis reveals 2+ blood with red cells and red cell casts. Further laboratory
tests include a complete blood count (CBC), serum electrolytes, BUN, creatinine, glucose, antinuclear antibodies (ANAs), and serum complement
levels (C3 and C4). All of these tests are within normal limits. Immunofluorescence examination of a renal biopsy from this patient reveals the
presence of large, irregular deposits of IgA/C3 in the mesangium. A linear
staining pattern is not found. What is the most likely diagnosis for this
patient?
a.
b.
c.
d.
e.
Berger’s disease
Focal segmental glomerulosclerosis
Goodpasture’s disease
Lipoid nephrosis
Membranoproliferative glomerulonephritis
6-44. A 45-year-old female treated for ovarian cancer develops difficulty
hearing. Which of the following agents most likely caused these findings?
a.
b.
c.
d.
e.
Paclitaxel
Doxorubicin
Bleomycin
5-FU
Cisplatin
132
Clinical Vignettes for the USMLE Step 1
6-45. A 36-year-old man presents at his physician’s office complaining of
fever and headache. On examination, he had leukopenia and increased
liver enzymes, and inclusion bodies were seen in his monocytes. History
revealed that he was an outdoorsman and remembered removing a tick
from his leg. Which of the following diseases is most likely causing the
symptoms described?
a.
b.
c.
d.
e.
Lyme disease
Ehrlichiosis
Rocky Mountain spotted fever
Q fever
Tularemia (Francisella tularensis)
6-46. A patient who presents to the hospital with severe headaches develops convulsions and dies. At autopsy the brain grossly has a “Swiss cheese”
appearance due to the presence of numerous small cysts containing milky
fluid. Microscopically, a scolex with hooklets is found within one of these
cysts. What is the causative agent for this disease?
a.
b.
c.
d.
e.
Taenia saginata
Taenia solium
Diphyllobothrium latum
Echinococcus granulosa
Toxocara canis
6-47. Previously, you treated a 44-year-old man, a former intravenous
drug abuser, for acute hepatitis C infection. Several months later, it is clear
that the patient has chronic hepatitis and may need therapy with interferon. Which long-term complications of hepatitis C infection must you
discuss so that the patient can make an informed decision about treatment?
a.
b.
c.
d.
e.
Hepatoma and cirrhosis
Hepatic adenoma
Sclerosing cholangitis
Hemochromatosis
Lymphoma or leukemia
Block 6
Questions
133
6-48. A urologist refers a 20-year-old man because of hypospadias and
infertility. He has been sexually active since his early teens. Recently, he
married and, despite many attempts, his wife has been unable to become
pregnant. The likely site of his infertility is
a.
b.
c.
d.
Pretesticular
Testicular
Posttesticular
Idiopathic
6-49. A 65-year-old male presents with bradykinesia, tremors at rest, and
muscular rigidity. Physical examination reveals the patient to have a “masklike” facies. In this patient, where would intracytoplasmic eosinophilic
inclusions most likely be found?
a.
b.
c.
d.
e.
Basal ganglia
Caudate nucleus
Hippocampus
Midbrain
Substantia nigra
6-50. A 30-year-old male patient was seen by the emergency service and
reported a 2-week history of a penile ulcer. He noted that this ulcer did not
hurt. Which one of the following conclusions/actions is most valid?
a.
b.
c.
d.
e.
Draw blood for a herpes antibody test
Perform a dark-field examination of the lesion
Prescribe acyclovir for primary genital herpes
Even if treated, the lesion will remain for months
Failure to treat the patient will have no untoward effect, as this is a self-limiting
infection
This page intentionally left blank.
BLOCK 7
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
BLOCK 7
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Questions
7-1. A 17-year-old individual who is phenotypically female presents for
workup of primary amenorrhea and is found to have an XY karyotype. The
most likely diagnosis is
a.
b.
c.
d.
e.
Androgen insensitivity syndrome
Deficiency of 5-α-reductase
Kallmann’s syndrome
Mixed gonadal dysgenesis
Turner’s syndrome
7-2. An ill patient denied being bitten by insects. However, he had spent
some time in a milking barn and indicated that it was dusty. Of the following rickettsial diseases, which one has he most likely contracted?
a.
b.
c.
d.
e.
Scrub typhus
Rickettsialpox
Brill-Zinsser disease
Q fever
Rocky Mountain spotted fever (RMSF)
137
138
Clinical Vignettes for the USMLE Step 1
7-3. A 75-year-old man was rushed to the hospital from his retirement
community when he suddenly became confused and could not speak but
could grunt and moan. The patient could follow simple commands and did
recognize his wife and children although he could not name them or speak
to them. Additional immediate examination revealed weakness of the right
upper extremity. Several days later, a more comprehensive examination
revealed weakness and paralysis of the right hand and arm with increased
biceps and triceps reflexes. Paralysis and weakness were also present on the
lower right side of the face. Pain, temperature, and touch modalities were
mildly decreased over the right arm, hand, and face, and proprioception
was reduced in the right hand. The patient had regained the ability to articulate with great difficulty a few simple words but could not repeat even
simple two or three word phrases. Which artery or major branch of a large
artery suffered the occlusion that produced the observed symptoms?
a.
b.
c.
d.
e.
Anterior choroidal artery
Middle cerebral artery
Posterior communicating artery
Ophthalmic artery
Anterior cerebral artery
7-4. A neurological examination of a 75-year-old male reveals that when
the abdominal wall is stroked, the muscles of the abdominal wall of the
side of the body stimulated failed to contract. Other neurological tests
appeared normal. The likely region affected includes
a.
b.
c.
d.
e.
C1–C5 spinal segments
C6–T1 spinal segments
T2–T7 spinal segments
T8–T12 spinal segments
L1–L5 spinal segments
Block 7
Questions
139
7-5. A 63-year-old female is hospitalized secondary to markedly decreased
vision. She has no history of polydipsia or nocturia. Physical examination
finds bilateral sluggish light reflexes and a bitemporal hemianopsia. No
papilledema is present, and her urine specific gravity is within normal limits. A CT scan of the head finds a suprasellar mass with calcification. What
is the most likely diagnosis for this tumor?
a.
b.
c.
d.
e.
Craniopharyngioma
Germinoma
Juvenile pilocytic astrocytoma
Medulloblastoma
Meningioma
7-6. A 55-year-old woman manager of a regional long-distance telephone
office whom you examine for the first time feels well. You do a complete
physical examination, which is normal except for a few very small palpable
and moveable, nontender nodes in both cervical chains and occasional
wheezes in the lungs. However, her laboratory studies show the following
hepatitis B virus profile: negative HBsAg, positive anti-HBs, low levels of IgG
anti-HBc, negative anti-HBeAg, and positive anti-HBe. The most likely diagnosis is
a.
b.
c.
d.
e.
Acute HBV infection, high infectivity
Late-acute HBV, low infectivity
Recovered from HBV infection
Chronic HBV infection, high infectivity
Immunization with HBsAg vaccine
7-7. A 75-year-old female in congestive heart failure (CHF) is unable to
climb a flight of stairs without experiencing shortness of breath. Digoxin is
administered to improve cardiac muscle contractility. Within two weeks,
she has a marked improvement in her symptoms. What cellular action of
digoxin accounts for this?
a.
b.
c.
d.
e.
Inhibition of cyclic adenosine 5′-monophosphate (cAMP) synthesis
Inhibition of mitochondrial calcium (Ca2+) release
Inhibition of the sodium (Na+) pump
Inhibition of β-adrenergic stimulation
Inhibition of adenosine triphosphate (ATP) degradation
140
Clinical Vignettes for the USMLE Step 1
7-8. A 55-year-old man who is being treated for adenocarcinoma of the lung
is admitted to a hospital because of a temperature of 38.9°C (102°F), chest
pain, and a dry cough. Sputum is collected. Gram’s stain of the sputum is
unremarkable and culture reveals many small Gram-negative rods able to
grow only on a charcoal yeast extract agar. This organism most likely is
a.
b.
c.
d.
e.
Klebsiella pneumoniae
Mycoplasma pneumoniae
Legionella pneumophila
Chlamydia trachomatis
S. aureus
Block 7
Questions
141
7-9. A female patient falls on an icy sidewalk and complains of her thumb
hurting. You take her x-ray and show her there are no fractures. However,
she asks what the small light circles (arrow) on the x-ray are. You explain
they are sesamoid bones in the tendon of the
a.
b.
c.
d.
e.
Flexor pollicis longus
Flexor pollicis brevis
Adductor pollicis
Abductor pollicis longus
Abductor pollicis brevis
142
Clinical Vignettes for the USMLE Step 1
7-10. A 55-year-old male describes bilateral pain in his lower back and
legs with prolonged standing while working on an assembly line. Whenever he sits down and takes a break, he gets some relief, but it recurs when
he resumes his job. No other inciting events can be identified. The most
likely cause of this problem is
a.
b.
c.
d.
Degenerative joint disease
Degenerative disk disease
Peripheral vascular disease
Lumbar spinal stenosis
7-11. During an office visit, a 40-year-old female reports that she is awakened in the middle of the night by intense jaw pain and often is gritting or
grinding her teeth. Relaxing the jaw does not help ease the pain. She is a
very active, social, and energetic person. From your experience with previous patients suffering from temporomandibular disorders, you suspect that
the primary causal link is
a.
b.
c.
d.
e.
Muscular fatigue
Physical trauma
Muscular or joint infection
Anxiety or depression
Early rheumatoid arthritis
7-12. A 10-month-old, previously healthy male infant develops a severe,
watery diarrhea 2 days after visiting the pediatrician for a routine checkup.
The most likely diagnosis is
a.
b.
c.
d.
e.
Rotavirus infection
Enterotoxigenic E. coli infection
Entamoeba histolytica infection
Lactase deficiency
Ulcerative colitis
Block 7
Questions
143
7-13. As a primary care practitioner, a middle-aged patient of yours seeks
advice about her aging parents. She is concerned about what to expect in
terms of declining cognitive and physiologic function, and in terms of providing for health care. Which of the following statements to her would be
accurate?
a. Twenty percent of aged persons live in long-stay institutions (nursing homes,
mental hospitals, homes for the aged)
b. The majority of old people feel bad most of the time
c. Aged drivers have more accidents per person than drivers under age 65
d. All five senses tend to decline in old age
e. Personality traits become unstable in the elderly
7-14. An individual is diagnosed with retinitis pigmentosa, which produces a defective opsin. This defect will most likely result in
a.
b.
c.
d.
e.
Degeneration of area 17 of the cerebral cortex
Degeneration of cone cells
Loss of central vision
Total loss of vision
Reduced response to light
7-15. A term infant is born at home and does well with breast-feeding.
Two days later, the mother calls frantically because the baby is bleeding
from the umbilical cord and nostrils. The most likely cause is
a.
b.
c.
d.
Deficiency of vitamin C due to a citrus-poor diet during pregnancy
Hypervitaminosis A due to ingestion of beef liver during pregnancy
Deficiency of vitamin K because infant intestines are sterile
Deficiency of vitamin K because of disseminated intravascular coagulation (disseminated clotting due to infantile sepsis)
e. Deficiency of vitamin E due to maternal malabsorption during pregnancy
7-16. A 19-year-old college student develops a rash. She works part-time
in a pediatric AIDS clinic. Her blood is drawn and tested for specific antibody to the chickenpox virus (varicella-zoster). Which of the following
antibody classes would you expect to find if she is immune to chickenpox?
a.
b.
c.
d.
e.
IgA
IgD
IgE
IgG
IgM
144
Clinical Vignettes for the USMLE Step 1
7-17. A husband and wife, both in their mid-thirties, have been patients of
yours for over 10 years. In the past, the husband has unsuccessfully been
treated for alcohol abuse. The wife has asked that the two of them be seen
together to discuss what might be of help with any of their related health
problems. In the discussion of individual and family stress, the husband
asked if medicine had anything to offer for his condition. As you are
explaining the benefits and risks of disulfiram (Antabuse), the wife explains
that her husband now drinks even more than before. At this point, the husband becomes angry and shouts, “I don’t need Antabuse, Alcoholics Anonymous, or anything else! I know I may have a drinking problem, but I can
handle it myself without anybody’s help!” In the above scenario, the husband is demonstrating
a.
b.
c.
d.
e.
Displacement
Denial
Projection
Rationalization
Reaction formation
7-18. A 40-year-old female with duodenal ulcers is treated with a combination of agents that includes clarithromycin. Of the following enzymes,
which is inactivated by clarithromycin?
a.
b.
c.
d.
e.
Dihydrofolate reductase
Glucose-6-phosphate dehydrogenase
Cytochrome P450
Na+,K+-ATPase
Na+,K+,Cl− co-transporter
Block 7
Questions
145
7-19. A 72-year-old male presents in the Emergency Room with dizziness
and nystagmus. Examination reveals a loss of pain and temperature sensation over the right side of the face and the left side of the body. The patient
exhibits ataxia and intention tremor on the right in both the upper and
lower extremities and is unable to perform either the finger-to-nose or heelto-shin tasks on the right. In addition, he is hoarse and demonstrates pupillary constriction and drooping of the eyelid on the right. Finally, the right
side of his face is drier than the left. Following vascular blockage, necrotic
damage in which of the following would explain the patient’s hoarseness?
a.
b.
c.
d.
e.
Nucleus ambiguus
Lateral spinothalamic tract
Spinal nucleus of CN V
Descending sympathetic pathways
Inferior cerebellar peduncle
7-20. You are running a community health clinic in a rural area where the
patient population is mainly of low socioeconomic status. You would expect
that the illness that is least likely to occur in higher rates than the general
population is
a.
b.
c.
d.
e.
Iatrogenic illness
Chronic illness
Obesity
Hypertension
Coronary artery disease
7-21. A 38-year-old male with AIDS presents with decreasing mental status. The workup at this time includes a spinal tap. Cerebrospinal fluid
(CSF) is stained with a mucicarmine stain and india ink. The mucicarmine
stain reveals numerous yeasts that stain bright red. The india ink prep
reveals through negative staining that these yeasts have a capsule. What is
the most likely diagnosis?
a.
b.
c.
d.
e.
Chromomycosis
Coccidioidomycosis
Cryptococcosis
Cryptosporidiosis
Paracoccidioidomycosis
146
Clinical Vignettes for the USMLE Step 1
7-22. A 59-year-old male with a history of rheumatic heart disease is
found to have atrial fibrillation (AF), for which he is treated with digoxin.
Treatment with digoxin converts his AF to a normal sinus rhythm and most
likely results in a decrease in which of the following?
a.
b.
c.
d.
The length of the refractory period
The velocity of shortening of the cardiac muscle
The conduction velocity in the atrioventricular (AV) node
The atrial maximum diastolic resting potential
7-23. A patient with neurological problems has an elevated cerebrospinal
fluid (CSF) antibody titer to measles virus. You would most likely suspect
a.
b.
c.
d.
e.
Fifth disease
Susceptibility to chickenpox
Possible subacute sclerosing panencephalitis (SSPE)
Possible hepatitis B infection
Acute Lyme disease
7-24. A 54-year-old male alcoholic presents with the sudden onset of
severe, constant epigastric pain that radiates to his midback. Further evaluation finds fever, steatorrhea, and discoloration around his flank and
umbilicus. Laboratory tests find elevated serum levels of amylase and
lipase. What is the most likely cause of these findings?
a.
b.
c.
d.
e.
Acute appendicitis
Acute cholangitis
Acute cholecystitis
Acute diverticulitis
Acute pancreatitis
7-25. A person is told that he has astigmatism. To correct this defect, the
optometrist prescribes a
a.
b.
c.
d.
e.
Cylindrical lens because the cornea or lens is oblong
Concave lens because the eyeball is too long
Convex lens because the lens is too short
Neutral lens because the eyeball is normal but the cornea is too thin
Concave lens because the cornea is opaque
Block 7
Questions
147
YOU SHOULD HAVE COMPLETED APPROXIMATELY
25 QUESTIONS AND HAVE 30 MINUTES REMAINING.
7-26. A 60-year-old male develops elevation of blood pressure, hyperglycemia, decreased bone density, and occult blood in his stool. Which of
the following agents is associated with these adverse effects?
a.
b.
c.
d.
e.
Hydrochlorothiazide
Pamidronate
Finasteride
Prednisone
Metformin
7-27. Postmortem histologic sections are taken from the liver of a 19-yearold female who died from an overdose of acetaminophen. These specimens
would most likely reveal
a.
b.
c.
d.
e.
Centrilobular necrosis
Focal scattered necrosis
Geographic necrosis
Midzonal necrosis
Periportal necrosis
148
Clinical Vignettes for the USMLE Step 1
7-28. Patients who are extremely allergic to bee stings will self-administer
epinephrine when stung. The activation of adrenergic beta-receptors by the
injected epinephrine will decrease
a.
b.
c.
d.
e.
The contraction of airway smooth muscle
The strength of ventricular muscle contraction
The rate of depolarization in the SA node
The transport of calcium into skeletal muscle fibers
The rate of glycogenolysis in the liver
7-29. A 22-year-old female who requests a postcoital contraceptive after
being raped would best be treated with which of the following?
a.
b.
c.
d.
e.
Mifepristone
Spironolactone
Aminoglutethimide
Leuprolide
Fludrocortisone
7-30. A child comes to an emergency room because of an infected dog
bite. The wound is found to contain small Gram-negative rods. The most
likely cause of infection is
a.
b.
c.
d.
e.
E. coli
H. influenzae
Pasteurella multocida
Brucella canis
Klebsiella rhinoscleromatis
7-31. A patient suffers from adenosine deaminase (ADA) deficiency, an
autosomal recessive immune deficiency in which bone marrow lymphoblasts cannot replicate to generate immunocompetent lymphocytes.
The treatment option that would permanently cure the patient is
a. Germ-line gene therapy to replace one ADA gene copy
b. Germ-line gene therapy to replace both ADA gene copies
c. Somatic cell gene therapy to replace one ADA gene copy in circulating lymphocytes
d. Somatic cell gene therapy to replace both ADA gene copies in circulating lymphocytes
e. Somatic cell gene therapy to replace one ADA gene copy in bone marrow lymphoblasts
Block 7
Questions
149
7-32. A 55-year-old woman complains of headaches and is subsequently
diagnosed as having a tumor localized to the left parietal lobe. In addition
to a variety of sensory deficits, further examination also reveals a reduction
in her visual fields. The most likely visual deficit would include
a.
b.
c.
d.
e.
Left homonymous hemianopsia
Right homonymous hemianopsia
Left upper quadrantanopia
Right upper quadrantanopia
Right lower quadrantanopia
7-33. You have taken on a part-time responsibility as the company physician for a small factory that has a mixture of hourly workers, engineers, and
executives. The company is under stress because of falling profits and competition with foreign manufacturers. You are aware of a number of stresses
in the workplace from uncertainty about the future of the company to
interpersonal conflict. Which of the following psychological stresses is
likely to have the most adverse impact on physical health?
a.
b.
c.
d.
e.
Regressiveness
Interpersonal conflict
Confusion
Uncontrollability
Fearfulness
7-34. Radiation treatment for a pituitary tumor in an 8-year-old boy
resulted in the complete loss of pituitary function. As a result, the child is
likely to experience
a.
b.
c.
d.
e.
Hypothyroidism and goiter
Increased ACTH
Absent sexual maturation
Accelerated growth spurts
Increased TSH levels
150
Clinical Vignettes for the USMLE Step 1
7-35. A 40-year-old male suspected of having adrenal insufficiency is
treated with a synthetic derivative of cosyntropin to assess adrenocortical
activity. Which of the following enzymes is activated by cosyntropin?
a.
b.
c.
d.
e.
f.
Adenyl cyclase
Mitogen-activated protein kinase
Phosphoinositol 3-kinase
Acetylcholinesterase (AChE)
Phospholipase C
Cyclic guanosine 5′-monophosphate (cGMP) phosphodiesterase
Block 7
Questions
151
7-36. Your patient just took up jogging in the evening for exercise and
complains that after a mile or so his left “leg” begins to hurt. You question
him on regions of the body or movements that do or do not evoke pain and
find that it is widespread throughout his left lower limb. Based on the location of the constriction of the artery (indicated by the arrow), what compartment or movement would you think would be least affected by the
reduced arterial blood flow?
a.
b.
c.
d.
e.
Gluteal region
Flexion of the thigh
Extension of the leg
Posterior thigh
Plantar flexion of the foot
152
Clinical Vignettes for the USMLE Step 1
7-37. A couple has three girls, the last of whom is affected with cystic
fibrosis. The first-born daughter marries her first cousin—that is, the son
of her mother’s sister—and they have a son with cystic fibrosis. The father
has a female cousin with cystic fibrosis on his mother’s side. Select the pedigree that best represents this family history from the diagrams below.
a.
b.
c.
d.
e.
f.
g.
h.
Diagram A
Diagram B
Diagram C
Diagram D
Diagram E
Diagram F
Diagram G
Diagram H
Block 7
Questions
153
7-38. Two days after admission, a 57-year-old man suddenly has a seizure.
He was undergoing evaluation for substernal chest pain. The nursing staff
noted that he seemed to be a little shaky since shortly after arrival on the
floor. He has no history of seizures and a stat CT of the head performed
during the postictal state was normal. Laboratory results had shown an
MCV of 101 (elevated) and his AST was mildly elevated (one and one-half
normal). In this patient, the most likely imbalance that would contribute to
this event would be
a.
b.
c.
d.
e.
Folate deficiency
Fasting hypoglycemia
Hypomagnesemia
Thiamine deficiency
Vitamin B12 deficiency
7-39. A 30-year-old man comes to your office with complaints of fatigue,
anorexia, nausea, and vomiting. He does not have fever. His urine is dark.
On physical examination, his liver is slightly enlarged and minimally tender. He does not have edema or spider angiomata. Laboratory tests show
the following: negative HBsAg, negative IgM anti-HAV, positive IgM antiHBc, and negative anti-HCV. The most likely diagnosis is
a.
b.
c.
d.
e.
Acute hepatitis A
Acute hepatitis B
Acute hepatitis A and B
Chronic hepatitis B
Acute hepatitis C
7-40. A 35-year-old male is diagnosed with primary syphilis. Which of the
following agents is the best choice for treating this patient?
a.
b.
c.
d.
e.
A first-generation cephalosporin
Oxacillin
Imipenen
Benzathine penicillin G
Vancomycin
154
Clinical Vignettes for the USMLE Step 1
7-41. A patient stung by a bee is rushed into the emergency room with a
variety of symptoms including increasing difficulty in breathing due to
vasal and bronchial construction. While your subsequent treatment is to
block the effects of histamine and other acute-phase reactants released by
most cells, you must also block the slow-reacting substance of anaphylaxis
(SRS-A), which is the most potent constrictor of the muscles enveloping
the bronchial passages. What is SRS-A composed of?
a.
b.
c.
d.
e.
Thromboxanes
Interleukins
Complement
Leukotrienes
Prostaglandins
7-42. A 55-year-old man discovered that he had pain in the neck and right
arm and weakness in extending his fingers of his right hand with loss of
sensation in the right thumb and middle fingers. A neurological examination further revealed a weakness of the right biceps reflex, but other neurological signs could not be detected. The most likely diagnosis of this
individual is
a. Syringomyelia involving the cervical cord
b. A knife wound of the right arm completely severing nerves innervating the
biceps muscle
c. Prolapse of a cervical disk
d. Poliomyelitis involving the cervical cord
e. AIDS
7-43. A 37-year-old female with Graves’ disease who requires antithyroid
therapy becomes pregnant. Which antithyroid drug is safest?
a.
b.
c.
d.
Potassium iodide (KI)
Methimazole
PTU
Potassium perchlorate (KClO4)
Block 7
Questions
155
7-44. Fever of unknown origin in a farmer who raises goats would most
likely be caused by which of the following organisms?
a.
b.
c.
d.
e.
Brucella melitensis
Clostridium novyi
T. pallidum
Histoplasma capsulatum
Mycobacterium tuberculosis
7-45. After receiving incompatible blood, a patient develops a transfusion
reaction in the form of back pain, fever, shortness of breath, and hematuria.
This type of immunologic reaction is classified as a
a.
b.
c.
d.
e.
Systemic anaphylactic reaction
Systemic immune complex reaction
Delayed type hypersensitivity reaction
Complement-mediated cytotoxicity reaction
T cell–mediated cytotoxicity reaction
7-46. A 55-year-old man was brought into the hospital with a severe burn
to his left hand. The man had placed his hand on the hot burner of an electric stove but had not sensed anything wrong until he smelled burning flesh.
Neurologic examination revealed loss of pain and temperature sensation
over dermatomes C4 through T6 bilaterally. However, pain and temperature
were perceived bilaterally both above C4 and below T6. Discriminative
touch was present in unburned dermatomes on the left and in the right
extremity. Although the left hand was too damaged to accurately assess
muscle function, weakness and wasting of small muscles of the right hand
was noted. Muscle strength and reflexes were otherwise normal. Pain and
temperature sensations from the extremities ascend in the spinal cord in the
a.
b.
c.
d.
e.
Intermediolateral cell column
Cuneate fasciculus
Lateral spinothalamic tract
Dorsal columns
Fasciculus gracilis
156
Clinical Vignettes for the USMLE Step 1
7-47. A man who was stabbed in the back during a fight is brought to the
emergency room. On examination you find impaired pain and temperature
sensation in one leg and impaired proprioception and vibration sense in
the opposite leg. These findings are descriptive of a
a.
b.
c.
d.
e.
Mononeuropathy
Brown-Séquard’s syndrome
Polyneuropathy
Mononeuropathy multiplex
Radiculopathy
7-48. A 30-year-old male presents with multiple soft, raised, beefy-red
superficial ulcers in his left groin. Physical examination reveals several
enlarged left inguinal lymph nodes. A histologic section from an enlarged
lymph node that is stained with a silver stain reveals characteristic Donovan bodies within macrophages. What is the most likely diagnosis?
a.
b.
c.
d.
e.
Chancroid
Gonorrhea
Granuloma inguinale
Lymphogranuloma venereum
Syphilis
7-49. A 40-year-old patient with a recent viral infection presents with a
significantly tender gland, low radioiodine uptake, and signs and symptoms of thyrotoxicosis. This presentation is most likely
a.
b.
c.
d.
e.
Graves’ disease
Subacute thyroiditis
Toxic multinodular goiter
Hashimoto’s thyroiditis
Toxic adenoma
7-50. An individual sustained a severe knife wound, damaging a spinal
nerve adjoining its entry to the spinal cord. If one could examine this
peripheral nerve and its cell body, which of the following events would he
or she most likely observe?
a.
b.
c.
d.
e.
A displacement of the nucleus toward the periphery of the cell
A mitotic division of the neuronal cell body
A more intense staining of the cell body
Degeneration of processes along the axon proximal but not distal to the lesion
An initial loss of mitochondria in the axoplasm at Ranvier’s node
BLOCK 8
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
This page intentionally left blank.
BLOCK 8
YOU HAVE 60 MINUTES
TO COMPLETE 50 QUESTIONS.
Questions
8-1. A 20-year-old male has a urethral discharge. Culture of the discharge
shows Neisseria gonorrhoeae. Which of the following agents is the best choice
for treating this patient?
a.
b.
c.
d.
e.
Ceftriaxone
Benzathine penicillin G
Imipenen
Amikacin
Sulfamethoxazole-trimethoprim
159
160
Clinical Vignettes for the USMLE Step 1
8-2. A 27-year-old female presents with headaches, muscle pain (myalgia), anorexia, nausea, and vomiting. She denies any history of drug or
alcohol use, but upon further questioning she states that recently she has
lost her taste for coffee and cigarettes. Physical examination reveals a slight
yellow discoloration of her scleras, while laboratory results indicate a
serum bilirubin level of 1.8 mg/dL, and aminotransferases (AST and ALT)
levels are increased. These signs and symptoms are most consistent with a
diagnosis of
a.
b.
c.
d.
e.
Gilbert’s syndrome
Chronic hepatitis
Amebic liver abscess
Acute viral hepatitis
Acute hepatic failure
Block 8
Questions
161
8-3. A 22-year-old male who belongs to a weekend football league presents in the ER. He was running with the ball when a defender tackled him
in the midthigh. The patient reports that when he got up, his thigh hurt, so
he sat out the rest of the game. When walking to the car, his posterior thigh
was extremely painful and swollen. After his shower, he noticed it was
becoming discolored with increased swelling. You are concerned about the
presence of a hematoma and a disruption of the arterial blood flow to the
hamstring muscles. An arteriogram is performed and the vessels in question (arrows) show good filling by contrast. These blood vessels are
a.
b.
c.
d.
e.
Descending branches of the inferior gluteal artery
Perforating branches of the deep femoral artery
Perforating branches from the obturator artery
Perforating branches of the femoral artery
Posterior femoral artery
162
Clinical Vignettes for the USMLE Step 1
8-4. A routine eye examination reveals the presence of inflammation limited to the left optic disk, probably due to neuritis of this region. The likely
visual deficit resulting from this disorder is
a.
b.
c.
d.
e.
Total blindness of the left eye
Left homonymous hemianopsia
Left heteronymous hemianopsia
Left enlargement of the blind spot
Left upper quadrantanopia
Block 8
Questions
163
8-5. A female infant was born prematurely after rupture of membranes
and, within 1 day of birth, developed a fever and died. The pregnant mother
had been cultured just prior to the birth of her child and her vaginal culture
revealed group B streptococci (S. agalactiae). Which one of the pictured tests
shown in the figure below would provide the most rapid and useful information?
A
C
B
D
a.
b.
c.
d.
Test A
Test B
Test C
Test D
164
Clinical Vignettes for the USMLE Step 1
8-6. An elderly woman is seen at your office with a complaint of loss of
vision in her left eye, which had been transient on a couple of occasions but
is now persisting. She has been seen recently at urgent care centers for multiple complaints including generalized fatigue, left-sided dull boring headaches with occasional sharp jabbing sensations, and arthritic complaint in
the hips. In addition, she reports some recent loss of 7 to 10 pounds. The
only remarkable finding on the routine labs obtained from her prior evaluations is an elevated alkaline phosphatase. You determine that the likely
cause of her condition is
a.
b.
c.
d.
Glaucoma
Brain tumor arising anterior to the optic chiasm
Optic neuritis
Temporal arteritis
8-7. A 30-year-old alcoholic with no apparent liver disease has decided to
abstain from alcohol. Shortly thereafter, he becomes agitated, anxious, has
visual hallucinations, is generally totally disoriented, and suffers bouts of
insomnia. Which of the following agents might be of use in averting these
findings?
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
Primidone
Disulfiram
Dextroamphetamine
Valproic acid
Phenylephrine
Phenytoin
Isoetharine
Carbamazepine
Amitriptyline
Triazolam
Diazepam
Block 8
Questions
165
8-8. A 28-year-old man is treated in an emergency room for a superficial
gash on his forehead. The wound is bleeding profusely, but examination
reveals no fracture. While the wound is being sutured, he relates that while
he was using an electric razor, he remembers becoming dizzy and then
waking up on the floor with blood everywhere. The physician suspects a
hypersensitive cardiac reflex. The patient’s epicranial aponeurosis (galea
aponeurotica) is penetrated, which results in severe gaping of the wound.
The structure overlying the epicranial aponeurosis is
a.
b.
c.
d.
e.
A layer containing blood vessels
Bone
The dura mater
The periosteum (pericranium)
The tendon of the epicranial muscles (occipitofrontalis)
8-9. A 3-month-old boy presents with poor feeding and growth, low muscle tone (hypotonia), elevation of blood lactic acid (lactic acidemia), and
mild acidosis (blood pH 7.3 to 7.35). The ratio of pyruvate to lactate in
serum is elevated, and there is decreased conversion of pyruvate to acetyl
coenzyme A in fibroblasts. Which of the following compounds might be
considered for therapy?
a.
b.
c.
d.
e.
Pyridoxine
Thiamine
Free fatty acids
Biotin
Ascorbic acid
8-10. A 60-year-old woman was hospitalized with a severe respiratory
infection for several weeks. Afterward, she displayed symptoms of myalgia
and weakness of the lower limbs. In addition, she also showed loss of muscle tone and some flaccidity with loss of tendon reflexes. Examination
also revealed a weakness of facial muscles. This constellation of symptoms
progressed for approximately 2 weeks and persisted for more than a year,
at which time, recovery took place at a slow rate. There was also some demyelination coupled with lymphatic inflammation at the site of demyelination. The most likely cause of this patient’s condition is
a.
b.
c.
d.
e.
Myasthenia gravis
Muscular dystrophy (MD)
Multiple sclerosis (MS)
Guillain-Barré syndrome
Lumbar disk prolapse
166
Clinical Vignettes for the USMLE Step 1
8-11. A 45-year-old male takes simvastatin for hypercholesterolemia; however, his cholesterol level remains above target at maximal doses. Cholestyramine is added to the therapeutic regimen. What drug-drug interaction can
occur?
a.
b.
c.
d.
The combination will not lower cholesterol more than either agent alone
The combination causes elevated very-low-density lipoprotein (VLDL)
Cholestyramine inhibits gastrointestinal (GI) absorption of simvastatin
Simvastatin is a direct antagonist of cholestyramine
8-12. A 52-year-old mother of three is at the stage of life when all three
children are moving away from home in pursuit of education and careers.
Sociological studies have shown that women who have launched their last
children most often report
a.
b.
c.
d.
e.
A less meaningful existence
More feelings of depression
Less positive self-concepts
Less stress
Fewer social activities
8-13. A 4-year-old African boy develops a rapidly enlarging mass that
involves the right side of his face. Biopsies of this lesion reveal a prominent
“starry sky” pattern produced by proliferating small, noncleaved malignant
lymphocytes. Based on this microscopic appearance, the diagnosis of
Burkitt’s lymphoma is made. This neoplasm is associated with chromosomal translocations that involve
a.
b.
c.
d.
e.
bcl-2
c-abl
c-myc
erb-B
N-myc
8-14. A 47-year-old male is seen in the medicine clinic with recently diagnosed mixed hyperlipidemia. An antihyperlipidemic is administered that
favorably affects levels of VLDL, low-density lipoprotein (LDL), and highdensity lipoprotein (HDL) and inhibits cholesterol synthesis. This drug is:
a.
b.
c.
d.
e.
Lovastatin
Colestipol
Niacin
Probucol
Neomycin
Block 8
Questions
167
8-15. A pediatric patient treated for grand mal seizures develops abnormal
values on liver function tests. Which of the following antiepileptic agents
would cause this to occur?
a.
b.
c.
d.
e.
Carbamezine
Valproic acid
Phenytoin
Phenobarbital
Gabapentin
8-16. A 45-year-old man presents for frontal bossing and enlarged nose,
tongue, and jaw. He has doughy palms and spadelike fingers. The best
screening test to establish the diagnosis is
a.
b.
c.
d.
e.
Random growth hormone
Insulin-like growth factor type 1 (IGF-1)
TSH
Prolactin
Fasting blood sugar
8-17. A 45-year-old woman is hospitalized for a cholecystectomy. She
appears to be anxious and worried about the surgery. Which type or types
of information provided to the patient will be most effective in reducing
stress?
a.
b.
c.
d.
e.
Sensory information
Procedural information
Coping information
Sensory and procedural information
Sensory and coping information
8-18. A 36-year-old female with a chronic UTI treated with ciprofloxacin
is not responsive to the antibiotic. Which of the following agents that she
might have been taking for other reasons would decrease the effectiveness
of ciprofloxacin?
a.
b.
c.
d.
e.
An antacid
An antihistamine
A nonsteroidal anti-inflammatory
An anxiolytic
A multivitamin not containing iron
168
Clinical Vignettes for the USMLE Step 1
8-19. A box of ham sandwiches with mayonnaise prepared by a person
with a boil on his neck was left out of the refrigerator for the on-call
interns. Three doctors became violently ill approximately 2 h after eating
the sandwiches. The most likely cause is
a.
b.
c.
d.
e.
S. aureus enterotoxin
Coagulase from S. aureus in the ham
S. aureus leukocidin
C. perfringens toxin
Penicillinase given to inactivate penicillin in the pork
8-20. A 33-year-old patient with an average menstrual cycle of 28 days
comes in for a routine Pap smear. It has been 35 days since the start of her
last menstrual period, and a vaginal smear reveals clumps of basophilic
cells. As her physician, you suspect
a.
b.
c.
d.
e.
She will begin menstruating in a few days
She will ovulate within a few days
Her serum progesterone levels are very low
There are detectable levels of hCG in her serum and urine
She is undergoing menopause
8-21. A culture of bacteria not resistant to tetracycline develops an infection from a virus that is derived from the lysis of tetracycline-resistant bacteria. Most of the bacterial progeny of the original culture is found to have
become resistant to tetracycline. What phenomenon has occurred?
a.
b.
c.
d.
e.
Conjugation
Colinearity
Recombination
Transformation
Transduction
Block 8
Questions
169
8-22. A 38-year-old woman is referred to a neurologist because she complained of visual loss and muscle weakness. Subsequent examination
revealed additional signs: impairment of other sensations, which included
tingling and burning sensations; weakness of the lower limbs; paralysis of
the upper limbs; progressive impairment of gait; signs of UMN involvement (i.e., spasticity and increased tendon reflexes); and bladder disturbances. No signs of infection were detected as measured by blood analysis,
cultures, and chest x-ray. However, elevations in CSF protein were noted as
well an abnormal IgG synthesis. Consequently, the neurologist’s diagnosis
of the patient was that she was suffering from
a.
b.
c.
d.
e.
Diffuse cerebellar degeneration
ALS
Multiple sclerosis MS
A peripheral neuropathy
A prefrontal cortical brain tumor
8-23. An individual comes upon an automobile accident in which someone is injured, but does not appear to be in a life-threatening situation. Of
the following factors that would determine whether the individual would
avoid taking action or volunteer to help, which would be likely to influence
the individual to avoid taking action?
a.
b.
c.
d.
e.
Perception that the other person is intoxicated
Proximity to the other person
Knowledge of what to do
Few others in the immediate area
Male gender of bystander
8-24. A 65-year-old woman is seen for evaluation of dementia. On examination, you note that her left pupil does not react well to light. When she
follows your finger with her eyes, as you approach the bridge of her nose,
you note the left pupil to constrict equally as well as the right one. The
most important test to order at this point would be
a.
b.
c.
d.
e.
Titer for Lyme disease
B12 level
RPR
HIV
Fasting glucose
170
Clinical Vignettes for the USMLE Step 1
8-25. A male patient is brought to the emergency department (ED) following ingestion of an unknown substance. He is found to have an elevated
temperature, hot and flushed skin, dilated pupils, and tachycardia. Of the
following, which would most likely cause these findings?
a.
b.
c.
d.
e.
Propranolol
Methylphenidate
Prazosin
Guanethidine
Atropine
Block 8
Questions
171
YOU SHOULD HAVE COMPLETED APPROXIMATELY
25 QUESTIONS AND HAVE 30 MINUTES REMAINING.
8-26. An immigrant from eastern Europe is rushed into the emergency
room with nausea, vomiting, diarrhea, and abdominal pain. His family
indicates he has eaten wild mushrooms. They have brought a bag of fresh,
uncooked mushrooms from a batch he had not yet prepared. You note the
presence of Amanita phalloides, the death-cap mushroom. A liver biopsy
indicates massive hepatic necrosis. Care is supportive. A major toxin of the
death-cap mushroom is the hepatotoxic octapeptide α-amanitin, which
inhibits
a.
b.
c.
d.
e.
DNA primase
RNA nuclease
DNA ligase
RNA polymerase
RNA/DNA endonuclease
172
Clinical Vignettes for the USMLE Step 1
8-27. A 38-year-old male presents with right lower quadrant abdominal
pain, fever, and a peripheral neutrophilia. An emergency appendectomy is
performed, but the appendix is found to be grossly unremarkable. Instead,
the lymph nodes surrounding the appendix are found to be enlarged,
inflamed, and matted together. Which one of the listed organisms is the
most likely cause of these abnormalities?
a.
b.
c.
d.
e.
Enteropathic Escherichia coli
Enterobius vermicularis
Trichomonas hominis
Yersinia enterocolitica
Bacillus anthracis
8-28. A 36-year-old male unemployed dishwasher with no history of
seizures presents with difficulty thinking coherently and claims that he is
an astronaut. Following treatment, he suddenly has a grand mal seizure.
Which neuroleptic agent was administered?
a.
b.
c.
d.
e.
Haloperidol
Fluphenazine
Clozapine
Molindone
Loxapine
8-29. An immigrant family from rural Mexico brings their 3-month-old
child to the emergency room because of whistling inspiration (stridor) and
high fever. The child’s physician is perplexed because the throat examination shows a gray membrane almost occluding the larynx. A senior physician recognizes diphtheria, now rare in immunized populations. The child
is intubated, antitoxin is administered, and antibiotic therapy is initiated.
Diphtheria toxin is often lethal in unimmunized persons because it
a. Inhibits initiation of protein synthesis by preventing the binding of GTP to the
40S ribosomal subunit
b. Binds to the signal recognition particle receptor on the cytoplasmic face of the
endoplasmic reticulum receptor
c. Shuts off signal peptidase
d. Blocks elongation of proteins by inactivating elongation factor 2 (EF-2, or
translocase)
e. Causes deletions of amino acid by speeding up the movement of peptidyl-tRNA
from the A site to the P site
Block 8
Questions
173
Questions 8-30 through 8-32
A 56-year-old woman experiences a loss of taste affecting the front of
her tongue and the ability to smile as a result of an infection.
8-30. If the sensory loss involves damage of cell bodies, the specific group
of neurons so affected would be the
a.
b.
c.
d.
e.
Otic ganglion
Nodose (inferior) ganglion
Pterygopalatine ganglion
Geniculate ganglion
Trigeminal ganglion
8-31. The cranial nerve most immediately affected is
a.
b.
c.
d.
e.
Nerve V
Nerve VI
Nerve VII
Nerve IX
Nerve X
8-32. The components of the nerve that is affected include
a.
b.
c.
d.
e.
General somatic afferent and general somatic efferent
Special visceral afferent and special visceral efferent
General visceral afferent and general somatic efferent
General somatic afferent and general visceral efferent
Special visceral afferent and general visceral efferent
8-33. In a presurgical patient, the great saphenous vein was cannulated in
the vicinity of the ankle. During the procedure, the patient experienced
severe pain that radiated along the medial border of the foot. Which of the
following nerves was accidentally included in a ligature during this procedure?
a.
b.
c.
d.
e.
Medial femoral cutaneous nerve
Saphenous nerve
Superficial fibular nerve
Sural cutaneous nerve
Tibial nerve
174
Clinical Vignettes for the USMLE Step 1
8-34. A farming couple in Northern Michigan consult their physician
about severe skin rashes and ulcers noted over the past year. They also have
lost many cattle over the past year, and claim that their cattle feed changed
in consistency and smell about 1 year ago. Chemical analysis of the feed
shows high concentrations of polychlorinated biphenyls, a fertilizer related
to known carcinogens. The physician sends the chemical to a laboratory for
carcinogen testing, which is performed initially and rapidly by
a. Inoculation of the chemical into nude mice
b. Incubation of mutant bacteria with the chemical to measure the rate of reverse
or “back” mutations
c. Incubation with stimulated white blood cells to measure the impact on DNA
replication
d. Computer modeling based on the structures of related carcinogens
e. Incubation with mammalian cell cultures to measure the rates of malignant
transformation
8-35. A 35-year-old woman comes to your office complaining of weakness
in her limbs and fatigability of her muscles, which, it seems to her, lessens
after she rests. Sometimes she does not have any muscle weakness, for
months at a time, and then she does; all this has been happening to her for
the past few years. She tells you that what bothers her most is the “droopiness” of her eyelids. Which one procedure provides definitive confirmation
of the diagnosis?
a.
b.
c.
d.
e.
Single-fiber electromyography
CT scan or MRI of the head
Antiacetylcholine receptor radioimmunoassay
Edrophonium chloride test
Electroencephalogram (EEG)
8-36. A 45-year-old male with alcoholic cirrhosis is seen in the ED
because of a laceration of the scalp. Of the following local anesthetics,
which would potentially be toxic?
a.
b.
c.
d.
Lidocaine
Benzocaine
Procaine
Tetracaine
Block 8
Questions
175
8-37. A 34-year-old male patient visits a physician with complaints of
fatigue, weight loss, night sweats, and “swollen glands.” The physician also
observes that he has an oral yeast infection. An HIV ELISA test is performed. The figure below demonstrates a Western blot for HIV. Based on
these results, and assuming a repeatedly reactive ELISA HIV screening test,
your best course of action is to
a.
b.
c.
d.
e.
Repeat the test immediately
Inform the patient that the test is falsely positive
Wait 6 weeks and repeat the test
Consider anti-HIV therapy
Order an HIV RNA test
8-38. After recovering from a viral respiratory tract infection, a 23-yearold female presents with weakness in her distal extremities that rapidly
ascends to involve proximal muscles. Physical examination reveals absent
deep tendon reflexes, and a lumbar puncture reveals the CSF protein to be
increased, but very few cells are present. A biopsy of a peripheral nerve
reveals inflammation and demyelination (radiculoneuropathy). What is the
best diagnosis?
a.
b.
c.
d.
e.
Brown-Séquard’s syndrome
Charcot-Marie-Tooth disease
Diabetes mellitus
Guillain-Barré syndrome
Syringomyelia
176
Clinical Vignettes for the USMLE Step 1
8-39. During the physical examination of a newborn child, it was
observed that the genitalia were female, but masculinized. The genotype
was determined to be 46,XX. Which of the following would be the most
likely cause of this condition?
a.
b.
c.
d.
e.
Androgen insensitivity
Decreased blood ACTH levels
Atrophy of the zona reticularis
A defect in the cortisol pathway
Hypersecretion of vasopressin
8-40. Parents of an adolescent male who have been in your primary care
practice consult you with regard to their concern about their son’s behavior. He has been truant from school and has engaged in several pranks with
friends that damaged the property of others. They ask about what might
predict delinquency in their son. Adolescent delinquency in boys can be
predicted most accurately on the basis of
a.
b.
c.
d.
e.
IQ
Physique or body type
Family size
Socioeconomic status of parents
Relationship with parents
8-41. You confirm acromegaly in a 58-year-old woman, and a MRI of the
pituitary shows a microadenoma. The best choice for treatment is
a.
b.
c.
d.
e.
Transsphenoidal surgery
Medical therapy with somatostatin agonist
Irradiation
Medical therapy with bromocriptine
Transfrontal surgery
8-42. A 60-year-old male alcoholic treated for type II diabetes mellitus
develops lactic acidosis. Which of the following oral hypoglycemic agents
might cause this adverse effect?
a.
b.
c.
d.
e.
Glyburide
Metformin
Acarbose
Rosiglitazone
Chlorpropamide
Block 8
Questions
177
8-43. A 70-year-old male is admitted to the emergency room and a subsequent MRI reveals the presence of a tumor involving parts of the left temporal lobe. In addition to certain short-term memory deficits, visual deficits
are noted as well. The most likely deficits will include
a.
b.
c.
d.
e.
Left homonymous hemianopsia
Right homonymous hemianopsia
Left upper quadrantanopia
Right upper quadrantanopia
Left lower quadrantanopia
8-44. It was determined that 95% of an oral 80-mg dose of verapamil was
absorbed in a 70-kg test subject. However, because of extensive biotransformation during its first pass through the portal circulation, the bioavailability
of verapamil was only 25%. Assuming a liver blood flow of 1500 mL/min,
the hepatic clearance of verapamil in this situation was
a.
b.
c.
d.
e.
60 mL/min
375 mL/min
740 mL/min
1110 mL/min
1425 mL/min
8-45. A 70-year-old female patient was readmitted to a local hospital with
fever and chills following cardiac surgery at a major teaching institution.
Blood cultures were taken and a Gram-positive coccus grew from the blood
cultures within 24 hours. Initial tests indicated that this isolate was resistant to penicillin. Further testing revealed that the isolate possessed the
group D antigen, was not β-lactamase-positive, but was resistant to vancomycin. The most likely identification of this isolate is
a.
b.
c.
d.
e.
Enterococcus faecalis
Enterococcus durans
Enterococcus cassiflavus
S. pneumoniae
Enterococcus faecium
178
Clinical Vignettes for the USMLE Step 1
8-46. A young child is brought into the hospital emergency room because
he has episodes of vomiting, headaches, problems in acquisition of motor
skills, cranial nerve dysfunction, and problems in breathing. This combination of syndromes most closely relates to which of the following disorders?
a.
b.
c.
d.
e.
Cleft palate
Hydrocephalus
Anencephaly
Syringomyelia
Congenital aneurysm
8-47. A 5-year-old girl is brought in with severe vomiting that has developed suddenly 5 days after she has had a viral infection. Upon questioning,
her parents indicate that she was given aspirin for several days to treat a
fever that occurred with the viral illness. She is hospitalized and quickly
develops signs of cerebral edema. Liver tissue reveals marked steatosis.
What is the most likely diagnosis?
a.
b.
c.
d.
e.
α1 antitrypsin deficiency
Dubin-Johnson syndrome
Hepatitis D infection
Reye’s syndrome
Wilson’s disease
8-48. Periodic hyperkalemic paralysis is characterized by high potassium
concentration and muscle weakness. Which of the following is likely to
cause muscle weakness as a result of increased extracellular potassium concentration?
a.
b.
c.
d.
e.
Hyperpolarization of muscle cells
Inactivation of sodium channels in muscle cells
Increased release of neurotransmitters from alpha motoneurons
Decreased potassium conductance in muscle cells
Increased duration of action potentials produced by alpha motoneurons
Block 8
Questions
179
8-49. A patient delays initiation of movement, displays an uneven trajectory in moving her hand from above her head to touch her nose, and is
uneven in her attempts to demonstrate rapid alternation of pronating and
supernating movements of the hand and forearm. She probably has a lesion
in the
a.
b.
c.
d.
e.
Hemispheres of the posterior cerebellar lobe
Flocculonodular lobe of the cerebellum
Vermal region of the anterior cerebellar lobe
Fastigial nucleus
Ventral spinocerebellar tract
8-50. A 19-year-old man living in New Mexico presents to a local clinic
after a 1-day history of fever, myalgia, chills, headache, and malaise. He
complains of vomiting, diarrhea, abdominal pain, tachypnea, and a productive cough. His white cell count is elevated with an increase in the
number of bands. Atypical lymphocytes are also found in the peripheral
blood. He is treated with antibiotics, but the next day he develops acute
respiratory failure with cardiopulmonary arrest and dies. Postmortem
examination of the lungs reveals intraalveolar edema, rare hyaline membranes, and a few interstitial lymphoid aggregates. The most likely cause of
this patient’s illness is infection with
a.
b.
c.
d.
e.
Ebola virus
Dengue fever virus
Hantavirus
Yellow fever virus
Alphavirus
This page intentionally left blank.
BLOCK 1
Answers
1-1. The answer is e. (Murray, 5/e, pp 128–129.) Because the boy
received his booster within the last 2 years, his level of immunity should be
adequate. If an individual has no history of immunization, both antitoxin
(passive immunization with tetanus immune globulin) for temporary and
fast protection and toxoid (toxin detoxified with formaldehyde) for future
and long-lasting protection should be given at different sites.
1-2. The answer is b. (Cotran, pp 1186–1187. Rubin, pp 1291–1292.)
Basal cell carcinoma, arising from the pluripotential cells in the basal layer
of the epidermis, is the most common tumor in patients with pale skin.
This carcinoma is locally invasive and may be quite destructive. Metastasis,
however, is quite rare. The classic clinical appearance is a pearly papule
with raised margins and a central ulcer. Variants, which are not infrequent,
include the superficial type (which may be multifocal), the morphea-like
type (which has marked fibrosis and is difficult to eradicate locally), and
the pigmented type (which may be mistaken clinically for malignant
melanoma). Histologically the cells are deeply basophilic with palisading at
the periphery of groups of tumor cells and peritumoral clefting. Abundant
eosinophilic cytoplasm may be seen in squamous cell carcinomas, not
basal cell carcinomas.
1-3. The answer is b. (Simon, pp 138–145.) Calcification of the internal
carotid artery could serve to disrupt nerve fibers proximal to it. One such
group of fibers includes parts of the optic nerve. In this case, the component of the right optic nerve affected includes the lateral aspect, or those
fibers that mediate vision associated with the nasal visual field of the right
eye. If the damage were more extensive and if it involved the entire nerve,
then total blindness of the right eye would have occurred.
1-4. The answer is c. (Ryan, pp 552–554.) HIV RT PCR, a nucleic acid
amplification test for HIV RNA, has recently been shown to be the most
181
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
182
Clinical Vignettes for the USMLE Step 1
valuable test for a) monitoring a patient’s progress during triple drug therapy and b) determining the chances of progression to AIDS. A viral load of
750,000 copies per ml significantly increases the chance of progression to
AIDS within 5 years. The other tests listed do not accurately predict progression to AIDS. The figure below shows the basic structure of HIV
including the enzyme, reverse transcriptase.
The location of the envelope glycoproteins (gp120 and gp124) is shown, as are the
major viral core proteins (p25, p17, p9, and p7).The core protein, p17, is found outside
the viral nucleoid and forms the matrix of the virion. RT indicates reverse transcriptase.
1-5. The answer is b. (Alberts, pp 734–749. Cotran, pp 92–93, 343–344.)
Many extracellular substances cause intracellular actions via secondmessenger systems. These second messengers may bind to receptors that
are located either on the surface of the cell or within the cell itself. Substances that react with intracellular receptors are lipid-soluble (lipophilic)
molecules that can pass through the lipid plasma membrane. Examples of
these lipophilic substances include thyroid hormones, steroid hormones,
and the fat-soluble vitamins A and D. Once inside the cell these substances
generally travel to the nucleus and bind to the hormone response element
(HRE) of DNA.
Block 1
Answers
183
Some substances that react with cell surface receptors bind to guaninenucleotide regulatory proteins. These proteins, called G proteins, may be
classified into four categories, namely Gs, Gi, Gt, and Gq. Two of these
receptors, Gs and Gi, regulate the intracellular concentration of cyclic
adenosine 5′-monophosphate (cAMP). In contrast, Gt regulates the intracytoplasmic levels of cyclic guanosine 5′-monophosphate (cGMP), and Gq
regulates the intracytoplasmic levels of calcium ions. Gs and Gi regulate
intracellular cAMP levels by their actions on adenyl cyclase, an enzyme
located on the inner surface of the plasma membrane that catalyzes the formation of cAMP from ATP. The adenylate cyclase G protein complex is
composed of the following components: the receptor, the catalytic enzyme
(i.e., adenyl cyclase), and a coupling unit. The coupling unit consists of
GTP-dependent regulatory proteins (G proteins), which may either be
stimulatory (Gs) or inhibitory (Gi). When bound to GTP and active, Gs
stimulates adenyl cyclase and increases cAMP levels. (Gs can be thought of
as the “on switch.”) In contrast, when bound to GTP and active, Gi inhibits
adenyl cyclase and decreases cAMP levels. (Gi can be thought of as the “off
switch.”) It is important to note that cholera toxin and pertussis toxin both
act by altering this adenyl cyclase pathway. Cholera toxin inhibits the conversion of Gs-GTP to Gs-GDP. In contrast, pertussis toxin inhibits the activation of Gi-GDP to Gi-GTP. Therefore, both cholera toxin and pertussis
toxin prolong the functioning of adenyl cyclase and therefore increase
intracellular cAMP, but their mechanisms are different. Cholera toxin keeps
the “on switch” in the “on” position, while pertussis toxin keeps the “off
switch” in the “off” position.
1-6. The answer is c. (Hardman, p 1183. Katzung, p 819.) Fluconazole penetrates into cerebrospinal fluid, where it is active against Cryptococcus neoformans. When it is given orally, blood levels are almost as high as when it is
given parenterally. Amphotericin is administered intravenously and does not
appear to be highly effective in fungal meningitis even when administered
intrathecally.
1-7. The answer is b. (Howard, pp 253–254.) Oxacillin- and methicillinresistant S. aureus (MRSA) has been rapidly increasing in incidence. MRSA
and methicillin-sensitive S. aureus (MSSA) coexist in heterologous populations. Treatment of a patient harboring this heterologous population may
provide a selective environment for the MRSA. Prior to changing therapy,
184
Clinical Vignettes for the USMLE Step 1
the susceptibility of the isolate should be determined. Vancomycin has
often been used effectively for MRSA, but it is expensive and nephrotoxic.
There is no evidence that MRSA is any more virulent or invasive than susceptible strains.
1-8 through 1-10. The answers are 1-8 d, 1-9 a, 1-10 d. (Afifi, pp
133–135. Kandel, pp 972–975.) Specialized peripheral receptors, which
specifically respond to changes in blood pressure, include the carotid
sinus (associated with cranial nerve IX) and the aortic arch (associated
with cranial nerve X). If these receptors (or the cell bodies associated with
these receptors) are damaged, then one of the fundamental regulatory
mechanisms for the control of blood pressure would be disrupted. The
results of such a disruption would likely lead to increases and instability
in blood pressure with evidence of spiking of blood pressure. Because
these sensory receptors in these structures respond to increases in blood
pressure, they are, in effect, stretch receptors and are consequently
referred to as baroreceptors. The principal projection of the axons associated with these baroreceptors is the solitary nucleus of the medulla, which
in turn, projects to autonomic nuclei such as the dorsal motor nucleus of
the vagus nerve, ventrolateral medulla, and higher regions associated with
autonomic functions, which include the PAG, hypothalamus, and limbic
system.
1-11. The answer is a. ( Junqueira, pp 318–319, 323, 324. Braunwald, pp
1715–1720.) Commonly, initial low levels of glucuronyl (glucuronysl) transferase in the underdeveloped smooth endoplasmic reticulum of hepatocytes
in the newborn result in jaundice (neonatal unconjugated hyperbilirubinemia); less commonly, this enzyme is genetically lacking. The neonatal small
intestinal epithelium also has an increased capacity for absorption of unconjugated bilirubin, which contributes to the elevated serum levels.
Bilirubin, a product of iron-free heme, is liberated during the destruction of old erythrocytes by the mononuclear macrophages of the spleen
and, to a lesser extent, of the liver and bone marrow. The hepatic portal system brings splenic bilirubin to the liver, where it is made soluble for excretion by conjugation with glucuronic acid. Increased plasma levels of
bilirubin (hyperbilirubinemia) result from increased bilirubin turnover,
impaired uptake of bilirubin, or decreased conjugation of bilirubin.
Increased bilirubin turnover occurs in Dubin-Johnson and Rotor syn-
Block 1
Answers
185
dromes, in which there is impairment of the transfer and excretion of
bilirubin glucuronide into the bile canaliculi. In Gilbert’s syndrome, there
is impaired uptake of bilirubin into the hepatocyte and a defect in glucuronyl transferase. In Crigler-Najjar syndrome, a defect in glucuronyl
transferase occurs in the neonate.
The ability of mature hepatocytes to take up and conjugate bilirubin
may be exceeded by abnormal increases in erythrocyte destruction
(hemolytic jaundice) or by hepatocellular damage (functional jaundice),
such as in hepatitis. Finally, obstruction of the duct system between the
liver and duodenum (usually of the common bile duct in the adult and
rarely from aplasia of the duct system in infants) results in a backup of
bilirubin (obstructive jaundice).
1-12. The answer is a. (Hardman, p 1146.) The “red man” syndrome is
associated with vancomycin, thought to be caused by histamine release.
Prevention consists of a slower infusion rate and pretreatment with antihistamines.
1-13. The answer is a. (Baum, pp 179–183.) J. K. Kiecolt-Glaser and B. A.
Esterling both reported studies of the changes that occur in the immune systems of caregivers who have been under the constant stress of caring for a
family member with Alzheimer’s disease for many months (average 33
months). A battery of immunologic assessments found that the caregivers
had suppressed immune systems; cellular immune system control of latent
viruses was poorer than that of a matched control group, the percentage of
T lymphocytes was lower, and the helper/suppressor ratio was smaller. The
data suggest that chronic and, at times, severe stress can cause persistent
changes in immunity. Furthermore, these changes can occur in several components of immunosurveillance.
In a study of residents living near Three Mile Island, Baum reported
that even six years after the nuclear accident, long-term stress resulted in
negative changes in the residents’ immune systems. This finding was indicated by poor cellular control over latent viruses, higher numbers of circulating neutrophils, and lower numbers of B cells and cytotoxic T
lymphocytes in the residents.
Thus, stress has a direct psychophysiologic effect on immunity. Some
bodily changes, such as increased levels of cortisol, can actually destroy
immune tissue. Stress also can change physiologic systems and may result
186
Clinical Vignettes for the USMLE Step 1
in increased drug use, smoking, and alcohol use, which can contribute to
negative chronic effects on the immune system.
There is some evidence that adaptation to stress can occur, but this
doesn’t appear to happen in more severe cases such as the caretakers of
patients with Alzheimer’s disease.
1-14. The answer is e. (Henry, pp 78–79, 657–659.) The differential diagnosis of microcytosis includes β thalassemia (due to a defect in globin
chain synthesis) and iron-deficiency anemia. It is important to distinguish
between these two disorders because therapy with iron benefits patients
with iron-deficiency anemia, but harms patients with thalassemia because
these patients are at risk for iron overload. Both thalassemia minor and
iron-deficiency anemia are microcytic disorders in which the mean corpuscular hemoglobin is usually found to be reduced. Red blood cell indexes
may be useful in differentiating the two disorders because, while the mean
corpuscular hemoglobin concentration (MCHC) is often normal or only
slightly reduced in association with thalassemia minor, the MCHC is often
definitely reduced in association with iron-deficiency anemia. (Both pernicious and folate-deficiency anemias lead to megaloblastic changes in erythrocytes.) The red cell distribution width (RDW) is a measure of variation
in the size of the red cells (anisocytosis). The RDW is increased in patients
with iron-deficiency anemia, but is normal in patients with β thalassemia.
Also unique to the microcytic anemias is the fact that patients with β thalassemia have increased red blood cell counts, while patients with all of the
other microcytic anemias have decreased red blood cell counts. This
increased red cell count in β thalassemia may be due to the increased
hemoglobin F, which shifts the oxygen dissociation curve to the left. This in
turn causes an increased release of erythropoietin. Unlike iron-deficiency
anemia, β thalassemia begins as a microcytic anemia. In contrast, irondeficiency anemia progresses through several stages. First there is
decreased storage iron, which is followed by decreased circulating iron. At
this time patients are still not clinically anemic. Next patients develop a
normocytic normochromic anemia that transforms into a microcytic normochromic anemia and finally a microcytic hypochromic anemia.
1-15. The answer is b. (Katzung, pp 504–505.) Amoxapine is a heterocyclic antidepressant that has effects on norepinephrine and serotonin
uptake. It is useful in psychotic patients who are depressed. The dopamin-
Block 1
Answers
187
ergic antagonism caused by amoxapine may lead to the amenorrheagalactorrhea syndrome.
1-16. The answer is b. (Rhoades, pp 380–383, 395–398.) Under normal
conditions, the V/Q ratio in both lungs is the same, so that mixed alveolar
gas in both lungs has the same PO2 and PCO2. The gas from the normal lung
will be approximately normal (PO2 = 100 mmHg, PCO2 = 40 mmHg). While
the gas from the occluded lung, which now represents alveolar dead space,
will resemble tracheal gas (PO2 = 150 mmHg, PCO2 = 0 mmHg). When the
gas from the two lungs mixes, the average alveolar O2 becomes 125 mmHg
and the average PCO2 becomes 20 mmHg.
1-17. The answer is a. (Katzung, p 668.) Fetal lung maturation is normally stimulated by cortisol produced in the fetal adrenal gland. When
preterm delivery with inadequate maturation of the lungs is anticipated,
large doses of glucocorticoid can be given to the mother to speed up the
physiologic process. Betamethasone is the preferred agent because it binds
to serum proteins to a lesser extent than cortisol and other glucocorticoids,
allowing more steroid to cross the placenta.
1-18. The answer is d. (Levinson, pp 271–279.) The advent of triple therapy or a therapeutic “cocktail” has had a marked effect on AIDS patients.
The combination of drugs work together as reverse transcriptive inhibitors
and a protease inhibitor. Patients improve rapidly, their CD4 lymphocyte
counts increase, and their HIV viral load is drastically reduced, often to
<50 copies per ml. On the other hand, an untreated HIV-positive patient
with a low CD4 and a high viral load a) is at increased risk of opportunistic infection and b) has a much greater chance of developing AIDS than if
the viral load was <50,000. The patient is infectious and his HIV antibody
screening test will be positive. The high viral load, however, is not a predictor of response to therapy. Many patients with high viral loads do very
well on triple therapy, although resistance to one or more of the agents may
subsequently occur. A low CD4 count does not predict progression to
AIDS but does indicate increased chance of opportunistic infection such as
those listed. Kaposi’s sarcoma, which has been linked to herpesvirus type
8, pneumocystis, and mycobacterial disease are three of the most prevalent
opportunistic infections. While HIV-positive patients contract pneumococcal pneumonia, they are probably at no more risk than the general popula-
188
Clinical Vignettes for the USMLE Step 1
tion, as protection against pneumococcal disease is linked to the presence
of anticapsular antibody.
1-19. The answer is c. (Katzung, pp 827–828.) Famciclovir is active
against herpes simplex and varicella zoster viruses. It is activated by a viral
kinase to a triphosphate. The triphosphate is a competitive substrate for
DNA polymerase. The incorporation of the famciclovir triphosphate into
viral DNA results in chain termination.
1-20. The answer is a. (Murray, pp 182–189. Scriver, pp 1521–1552. Sack,
pp 121–138. Wilson, pp 287–317.) Cyanide blocks respiration by displacing
oxygen from hemoglobin. Oxidative phosphorylation in the mitochondria
cannot proceed because cyanide cannot oxidize (remove electrons) from
reduced cofactors like NADH. The citric acid cycle is the major pathway for
generating ATP and reducing equivalents (NADH, H+) from catabolism of
carbohydrates, amino acids, and lipids. Inability to regenerate NAD+ from
NADH through mitochondrial oxidative phosphorylation depletes the cell
of NAD+ and inhibits the citric acid cycle. Failure to generate ATP by oxidative phosphorylation using NADH from the citric acid cycle depletes the
cell of energy and leads to cell and tissue death (organ failure). Enzymes
(citrate synthase, aconitase) and intermediates of the citric acid cycle (citrate, acetyl coenzyme A) need only be present in trace amounts because
they are not consumed.
1-21. The answer is d. (Ash, pp 32, 33, 231, 233, 322, 327.) Enterobius
(pinworm), Ascaris (roundworm), Necator (hookworm), and Trichuris
(whipworm) are roundworms, or nematodes. T. saginata (tapeworm), a
segmented flatworm, affects the small intestine of humans. Tapeworm segments, called proglottids, appear in the stool of infected persons.
1-22. The answer is a. (Murray, pp 190–198. Scriver, pp 4517–4554. Sack,
pp 121–138. Wilson, pp 287–317.) One of the world’s most common enzyme
deficiencies is glucose-6-phosphate-dehydrogenase deficiency (305900).
This deficiency in erythrocytes is particularly prevalent among African and
Mediterranean males. A deficiency in glucose-6-phosphate dehydrogenase
blocks the pentose phosphate pathway and NADPH production. Without
NADPH to maintain glutathione in its reduced form, erythrocytes have no
Block 1
Answers
189
protection from oxidizing agents. This X-linked recessive deficiency is
often diagnosed when patients develop hemolytic anemia after receiving
oxidizing drugs such as pamaquine or after eating oxidizing substances
such as fava beans.
1-23. The answer is a. (Guyton, pp 496–500.) Breathing air with a low
partial pressure of oxygen will stimulate the peripheral chemoreceptors
which, in turn, will stimulate respiration. The increased alveolar ventilation will decrease the arterial PCO2 to a value below normal (less than 40
mmHg). Although the increased ventilation will increase the arterial PO2,
the resulting value will remain below normal for as long as the individual
is breathing air with a low partial pressure of oxygen. A lower than normal
arterial O2 tension and a normal or greater than normal arterial CO2 tension is usually a sign of a depressed respiratory center. A greater than normal arterial O2 tension and a lower than normal arterial CO2 tension can
only occur if the person is breathing air with a greater than normal concentration of oxygen.
1-24. The answer is e. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp
57–84. Wilson, pp 123–148.) Children with chromosome abnormalities
often exhibit poor growth (failure to thrive) and developmental delay with
an abnormal facial appearance. This baby is too young for developmental
assessment, but the catlike cry should provoke suspicion of cri-du-chat
syndrome. Cri-du-chat syndrome is caused by deletion of the terminal
short arm of chromosome 5 [46,XX,del(5p), also abbreviated as 5p−] as
depicted in panel e. When a partial deletion or duplication like this one is
found, the parents must be karyotyped to determine if one carries a balanced reciprocal translocation. The other karyotypes show (a) deletion of
the short arm of chromosome 4 [46,XY,del(4p) or 4p−]; (b) XYY syndrome
(47,XYY); (c) deletion of the long arm of chromosome 13 [46,XX,del(13q)
or 13q−]; (d) Klinefelter’s syndrome (47,XXY). Most disorders involving
excess or deficient chromosome material produce a characteristic and recognizable phenotype (e.g., Down’s, cri-du-chat, or Turner’s syndrome). The
deletion of 4p− (panel A) produces a pattern of abnormalities (syndrome)
known as Wolf-Hirschhorn syndrome; deletion of 13q− produces a 13q−
syndrome (no eponym). The mechanism(s) by which imbalanced chromosome material produces a distinctive phenotype is completely unknown.
190
Clinical Vignettes for the USMLE Step 1
1-25. The answer is e. (Cotran, pp 1164–1166.) Tumors of the adrenal
medulla include pheochromocytomas, ganglioneuromas, and neuroblastomas. Pheochromocytomas are composed of cells that contain membranebound, dense-core neurosecretory granules and have high cytoplasmic levels
of catecholamines. Secretion of these catecholamines produces the characteristic symptoms associated with pheochromocytomas, such as hypertension,
palpitations, tachycardia, sweating, and glucose intolerance (diabetes mellitus). Pheochromocytomas are associated with the urinary excretion of catecholamines or their metabolic breakdown products. The catecholamines
include dopamine, norepinephrine, and epinephrine. These catecholamines
are broken down by two enzymes, catecholamine orthomethyltransferase
(COMT) and monoamine oxidase (MAO), into homovanillic acid,
normetanephrine, metanephrine, or vanillylmandelic acid (VMA). Any of
these metabolic products may be found in the urine of patients with
pheochromocytomas; however, VMA is most common. The best screening
tests are 24-h urinary metanephrine and VMA levels. Pheochromocytomas
have been called the “10% tumor” as 10% are malignant, 10% are multiple
(bilateral), 10% are extraadrenal, 10% calcify, and 10% are familial. These
familial tumors are associated with neurofibromatosis, MEN 2A, or MEN 2B.
1-26. The answer is c. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp
97–158. Wilson, pp 23–39.) Males always transmit their single X chromosome to their daughters. Therefore, a daughter of a male affected with an
X-linked disorder is an obligate carrier for that disorder. When the condition is X-linked recessive, as with most forms of color-blindness, the
daughter is unlikely to show any phenotypic evidence that she is carrying this abnormal gene. Offspring of female carriers are of four types:
(1) female carrier with one normal and one mutant allele, (2) normal
female with two normal alleles, (3) affected male with a single mutant
allele, and (4) normal male with a single normal allele. The chance of having an affected child is thus 1/4 or 25%. If the obligate carrier female gives
birth to a son, the chance of the son being color-blind is 50%.
1-27. The answer is e. (Katzung, pp 428–429.) Although a rare occurrence, halothane and other inhaled gas anesthetics may cause malignant
hyperthermia. Apparently, this occurs in genetically susceptible individuals. Its onset may be accelerated by the concomitant use of succinylcholine.
Immediate treatment includes administration of dantrolene.
Block 1
Answers
191
1-28. The answer is c. (Levinson, p 313.) Acanthamoeba is a free-living
ameba as is Naegleria. Naegleria usually causes severe, often fatal, meningoencephalitis, while Acanthamoeba is uncommonly isolated from contact
lens fluid and patients with retinitis who do not store their lenses under
sterile conditions. Acanthamoeba can be grown on nonnutrient agar plates
using Escherichia coli as a food source. They are identified microscopically
with use of a nonspecific fluorescent stain.
1-29. The answer is d. (Carlson, pp 259–267.) Most of the human research
on sleep has found that after a few days of sleep deprivation people report
perceptual distortions or, in a few cases, even hallucinations. These studies
have documented statements such as “the floor seems wavy” or “steam seems
to be rising from the floor,” indicating that sleep deprivation affects cerebral
functioning. Another research finding is that being sleepy is distinctly different from being tired, as after exercise. Sleepiness can occur even without any
activity and sleep deprivation does not appear to interfere with the ability to
perform physical exercise. Likewise, there is no evidence of a physiologic
stress response to sleep deprivation, indicated by little change in blood levels
of cortisol and epinephrine. Sleep does appear to be necessary for the brain
to function normally. After a period of sleep deprivation a rebound phenomenon does occur. The individual will sleep longer and spend a much greater
time in REM sleep, but will not regain the number of sleepless hours lost.
1-30. The answer is d. (Murray, pp 258–284. Scriver, pp 2863–2914. Sack,
pp 205–222. Wilson, pp 361–391.) This man has familial hypercholesterolemia (143890), an autosomal dominant phenotype defined by studying men who experienced heart attacks at young ages. Mutations in the
LDL receptor lead to decreased cellular cholesterol uptake and increased
serum cholesterol. Since LDL has a high cholesterol content, the LDL fraction is elevated compared to the HDL fraction on lipoprotein electrophoresis. In normal individuals, the LDL is taken up by its specific receptor and
imported via caveolae to the cell interior. Cholesterol then produces feedback inhibition on the rate-limiting enzyme of cholesterol synthesis
(hydroxymethylglutaryl CoA reductase) and also leads to a decrease in the
number of LDL receptors. In rare cases, two individuals with familial
hypercholesterolemia marry and produce a child with homozygous familial hypercholesterolemia. These children develop severe atherosclerosis
and xanthomas (fatty tumors) at an early age.
192
Clinical Vignettes for the USMLE Step 1
1-31. The answer is e. (Raoult, pp 619–628.) Koplik’s spots are pathognomonic for measles. The measles virus is a paramyxovirus. In industrialized countries, vaccination has reduced the importance of this childhood
infection (although U.S. incidence increased in 1989 and 1990). In developing countries, however, measles is a major killer of young children. In
America, most states now require proof of immunity before school enrollment, and this has reduced the incidence of disease.
1-32. The answer is e. (Katzung, pp 744, 748.) Vitamin D3 is hydroxylated
to 25-OHD3 (calcifediol). Calcifediol is then hydroxylated in the kidney to
the most active form of vitamin D, which is 1,25-dihydroxyvitamin D (calcitriol). Calcitriol has a rapid onset of action and a short half-life. The administration of calcitriol causes the elevation of serum Ca levels by enhancing the
intestinal absorption of Ca. Calcitriol is indicated in vitamin D deficiency,
particularly in patients with chronic renal failure or renal tubular disease,
hypoparathyroidism, osteomalacia, and rickets. Serum phosphate levels usually increase with prolonged treatment.
1-33. The answer is a. (Cotran, pp 1148–1151. Chandrasoma, pp 857–
863.) Hyperparathyroidism is caused by excess production of parathyroid
hormone (PTH). In patients with hyperparathyroidism, it is important to
distinguish primary hyperparathyroidism from secondary hyperparathyroidism. Both forms may be associated with the development of bone
lesions, but excess PTH production in primary hyperparathyroidism leads
to different laboratory values than those seen with secondary hyperparathyroidism. Increased levels of PTH in primary hyperparathyroidism
result in increased serum calcium (hypercalcemia) and decreased serum
phosphorus. The serum calcium levels are elevated because of increased
bone resorption and increased intestinal calcium absorption, the result of
increased activity of vitamin D. PTH also increases calcium reabsorption in
the distal renal tubule, but, because the filtered load of calcium exceeds the
ability for reabsorption, calcium is increased in the urine (hypercalciuria).
PTH also increases urinary excretion of phosphate. The excess calcium in
the urine predisposes to renal stone formation, especially calcium oxalate
or calcium phosphate stones. Urinary stones can produce flank pain and
hematuria. This is the most common presentation for patients with hyperparathyroidism. The hypercalcemia of hyperparathyroidism may also cause
peptic ulcer disease due to the stimulation of gastrin release and increased
Block 1
Answers
193
acid secretion from the parietal cells. The hypercalcemia also results in
muscle weakness, fatigue, and hypomotility of the GI tract, which can lead
to constipation and nausea. Alterations of mental status are also common.
In contrast to primary hyperparathyroidism, secondary hyperparathyroidism results from hypocalcemia. This causes secondary hypersecretion
of PTH and produces the combination of hypocalcemia and increased PTH
production. It is primarily found in patients with chronic renal failure.
Patients with hypoparathyroidism develop hypocalcemia and hyperphosphatemia but have normal serum creatinine levels. Primary hypoparathyroidism and pseudohypoparathyroidism also result in decreased 24-h
excretion of calcium and phosphate.
1-34. The answer is d. (Moore & Dalley, pp 669–670, 810.) The large
arrows indicate the proximal humeral epiphyseal plate. The young girl was
only 11 and still growing. The epiphyseal plates show up on x-rays as radiolucent cartilage and should not be confused with a fracture. The epiphysis
is located at the anatomic neck of the humerus but is not discoid-shaped
like many epiphyseal plates in long bones. This plate is tent-shaped, which
is why it is not clearly visible all the way across the proximal humerus.
1-35. The answer is b. (Murray, pp 190–198. Scriver, pp 1553–1588.
Sack, pp 121–138. Wilson, pp 287–317.) Lactose in breast milk and infant
formula is converted by intestinal lactase to glucose and galactose that are
efficiently absorbed. In galactosemia (230400), deficiency of galactose-1phosphate uridyl transferase prevents the conversion of galactose into
glucose-6-phosphate by the liver or erythrocytes. Most other organs do
not metabolize galactose. The severe symptoms of galactosemia are
caused by the reduction of galactose to galactitol (dulcitol) in the presence of the enzyme aldose reductase. High levels of galactitol cause
cataracts, the accumulation of galactose-1-phosphate contributes to liver
disease, and the accumulation of galactose metabolites in urine can be
measured as reducing substances by the Clinitest method. Any carbohydrate, including glucose, with a C1 aldehyde registers as a reducing substance by Clinitest, so a Dextrostix (glucose only) test is often performed
as a control. In normal children, galactose is first phosphorylated by
ATP to produce galactose-1-phosphate in the presence of galactokinase.
Next, galactose-1-phosphate uridyl transferase transfers UDP from UDPglucose to form UDP-galactose and glucose-1-phosphate. Under the
194
Clinical Vignettes for the USMLE Step 1
action of UDP-galactose-4-epimerase, UDP-galactose is epimerized to
UDP-glucose. Finally, glucose-1-phosphate is isomerized to glucose-6phosphate by phosphoglucomutase. Infants with suspected galactosemia
(230400) must be withdrawn from breast-feeding or lactose formulas
and placed on nonlactose formulas such as Isomil.
1-36. The answer is b. (Katzung, pp 493–494.) A decrease in thyroid function occurs in most patients on lithium. This effect is usually reversible or not
progressive, but a few patients develop symptoms of hypothyroidism. A
serum thyroid-stimulating hormone (TSH) concentration is recommended
every 6 to 12 months. “Browning” of vision, clinically described as pigmentary retinopathy, occurs with thioridazine. This is due to retinal deposition of
the drug. Although neurologic adverse effects (e.g., tremor, choreoathetosis,
motor hyperactivity, ataxia, dysarthria, and aphasia) can occur with lithium,
it does not cause the neuroleptic malignant syndrome associated with antipsychotic agents. Pseudodepression sometimes occurs in patients on antipsychotics. This may be related to drug-induced akinesia.
1-37. The answer is e. (Cotran, 6/e, pp 70–72.) Certain drugs are important in the control of acute inflammation because they inhibit portions of
the metabolic pathways involving arachidonic acid. For example, corticosteroids induce the synthesis of lipocortins, a family of proteins that are
inhibitors of phospholipase A2. They decrease the formation of arachidonic
acid and its metabolites, prostaglandins and leukotrienes. Aspirin,
indomethacin, and other nonsteroidal anti-inflammatory drugs (NSAIDs),
in contrast, inhibit cyclooxygenase and therefore inhibit the synthesis of
prostaglandins and thromboxanes. The prostaglandins have several important functions. For example, prostaglandin E2 (PGE2), produced within the
anterior hypothalamus in response to interleukin 1 secretion from leukocytes, results in fever. Therefore aspirin can be used to treat fever by
inhibiting PGE2 production. PGE2 is also a vasodilator that can keep a ductus arteriosus open. At birth, breathing decreases pulmonary resistance and
reverses the flow of blood through the ductus arteriosus. The oxygenated
blood flowing from the aorta into the ductus inhibits prostaglandin production and closes the ductus arteriosus. Therefore prostaglandin E2 can be
given clinically to keep the ductus arteriosus open, while indomethacin
can be used to close a patent ductus. Prostaglandin F2 (PGF2) causes uterine contractions, which can result in dysmenorrhea. Indomethacin can be
Block 1
Answers
195
used to treat dysmenorrhea by inhibiting the production of PGF2.
Bradykinin is a nonapeptide that increases vascular permeability, contracts
smooth muscle, dilates blood vessels, and causes pain. It is part of the kinin
system and is formed from high-molecular-weight kininogen (HMWK).
Histamine, a vasoactive amine that is stored in mast cells, basophils, and
platelets, acts on H1 receptors to cause dilation of arterioles and increased
vascular permeability of venules.
1-38. The answer is a. (McKenzie, pp 290–291, 393, 394. Junqueira, pp
279, 287–288, 298, 300, 430, 432, 433.) Photomicrographs A and B show two
distinctly different types of epithelium: stratified squamous epithelium of
the anus (top panel) and crypts (without villi) of the rectum (lower panel).
The anus has anal valves and an absence of the muscularis mucosa. The
esophageal-cardiac junction also represents a junction between stratified
squamous and simple columnar epithelium, but the cardiac portion of the
stomach forms the mucus-secreting cardiac glands with no goblet cells. The
junction of the stomach (pylorus) and duodenum represents the juncture of
two simple columnar epithelia, the pylorus containing the short (compared
with fundus) pyloric glands and the duodenum with crypts and villi as well
as the submucosal Brunner’s glands. Skin is keratinized. The cervical
mucosa contains extensive cervical glands, and the vaginal epithelium is
keratinized. In vagina and cervix, the GI tract pattern [epithelium, connective tissue (CT), muscle, CT, muscle, CT] is not present.
1-39. The answer is a. (Murray, pp 190–198. Scriver, pp 1521–1552. Sack,
pp 121–138. Wilson, pp 287–317.) Glycosides are formed by condensation
of the aldehyde or ketone group of a carbohydrate with a hydroxyl group
of another compound. Other linked groups (aglycones) include steroids
with hydroxyl groups (e.g., cardiac glycosides such as digitalis or ouabain)
or other chemicals (e.g., antibiotics such as steptomycin). Sucrose (α-Dglucose-β-1 → 2-D-fructose), maltose (α-D-glucose-α-1 → 4-D-glucose),
and lactose (α-D-galactose-β-1 → 4-D-glucose) are important disaccharides. Fructose is among several carbohydrate groups known as ketoses
because it possesses a ketone group. The ketone group is at carbon 2 in
fructose, and its alcohol group at carbon 1 (also at carbon 6) allows ketal
formation to produce pyranose and furanose rings as with glucose. Most of
the fructose found in the diet of North Americans is derived from the disaccharide sucrose (common table sugar). Sucrose is cleaved into equimo-
196
Clinical Vignettes for the USMLE Step 1
lar amounts of glucose and fructose in the small intestine by the action of
the pancreatic enzyme sucrase. Deficiency of sucrase can also cause chronic
diarrhea. Hereditary fructose intolerance (229600) is caused by deficiency
of the liver enzyme aldolase B, which hydrolyzes fructose-1-phosphate.
1-40. The answer is e. (Cotran, p 1129.) The syndrome of inappropriate
antidiuretic hormone (SIADH) is an important cause of dilutional hyponatremia that has been identified in tumors of the thymus gland, malignant
lymphoma, and pancreatic neoplasms. It occurs predominantly, however,
as a result of ectopic secretion of ADH by small cell carcinomas of the lung.
Since the tumor cells per se are autonomously producing ADH, there is no
feedback inhibition from the hypothalamic osmoreceptors, and the persistent ADH effect on the renal tubules causes water retention even with concentrated urine; hence the term inappropriate ADH. Laboratory findings
include low plasma sodium levels (dilutional hyponatremia), low plasma
osmolality, and high urine osmolality caused by disproportionate solute
excretion without water.
1-41. The answer is a. (Kandel, pp 936–947.) Paradoxical sleep is a term
given to REM sleep, which is considered paradoxical because its electroencephalographic pattern resembles that of the alert waking state. Dreaming
occurs during REM sleep. When a person is repeatedly awakened during
dreaming, a dream deprivation occurs and there is a rebound phenomenon
of increased frequency and lengthening of dreaming when the person is permitted to sleep normally. Dream deprivation does not result in a major
decrement in psychological or intellectual functions (as does sleep deprivation), but it does appear to retard the memory formation of emotionally
toned words. While earlier studies suggested the presence of bizarre behavior, anxiety, irritability, and nightmares, more recent studies have found no
such changes in humans even after 16 days of deprivation of dream sleep.
1-42. The answer is c. (Hardman, pp 415–416.) Neuroleptic malignant
syndrome is thought to be a severe form of an extrapyramidal syndrome
that can occur at any time with any dose of a neuroleptic agent. However,
the risk is higher when high-potency agents are used in high doses, especially if given parenterally. Mortality from NMS is greater than 10%.
1-43. The answer is e. (Kumar, pp 395–398. Braunwald, pp 1456–1460.
Junqueira, pp 335–336, 344.) The teenage patient is suffering from an asth-
Block 1
Answers
197
matic attack, probably allergen-induced. Mast cells are a key player in this
airway disease. Mast cells in the bronchioles are stimulated to release histamine and heparin that induce the contraction of smooth bronchiolar muscle and edema in the wall. If the bronchoconstriction is chronic, the
long-term result is thickening of the bronchiolar musculature. Other cells
involved in asthma include eosinophils, neutrophils, macrophages, and
lymphocytes, which signal to each other through a complex cytokine network. Mediators released include bradykinin, leukotrienes, and prostaglandins, which enhance bronchoconstriction, vascular congestion, and
edema. The airway epithelium also is involved in response to and release
of mediators. These muscle changes are usually accompanied by goblet
cell hypersecretion of a viscous mucus, which can obstruct the airway.
Eosinophils release proteins that destroy the airway epithelium (releasing
Creola bodies). T lymphocytes are also present in more severe “attacks”
and, along with B lymphocytes, may play a role in the initiation of allergic
asthma. T lymphocytes also release cytokines that activate cell-mediated
immunity pathways. Mucociliary transport is active in the trachea and
bronchi; alveolar macrophages do not play a role in that process.
1-44. The answer is e. (Murray, pp 48–73. Scriver, pp 2863–2914. Sack, pp
3–17. Wilson, pp 361–370.) Many enzymes interact to regulate blood clotting. Plasmin is activated by proteolytic cleavage of its zymogen, plasminogen. The activating protease is called tissue plasminogen activator (tPA).
Plasmin hydrolyzes fibrin clots to form soluble products, and is used to dissolve clots in coronary arteries that cause myocardial infarction. Platelets,
thrombin, and fibrinogen promote clotting through the intrinsic pathway
and would be contraindicated in myocardial infarction. Platelets form a
plug at the site of bleeding and bind prothrombin to facilitate its conversion to thrombin. Fibrinogen is the substrate acted upon by thrombin to
yield the fibrin mesh of blood clots. Heparin is a mucopolysaccharide that
terminates clot formation by interfering with a number of steps in the coagulation cascade. Heparin inhibits the formation of clots, but cannot dissolve clots that have already formed.
1-45. The answer is e. (Hardman, p 1523.) Administration of intravenous CaG would immediately correct the tetany that might occur in a
patient in whom a thyroidectomy was recently performed. Parathyroid
hormone would act more slowly but could be given for its future stabilizing effect. Long-term control of a patient after a thyroidectomy can be
198
Clinical Vignettes for the USMLE Step 1
obtained with vitamin D and dietary therapy. Calcitonin is a hypocalcemic
antagonist of parathyroid hormone. Plicamycin (mithramycin) is used to
treat Paget’s disease and hypercalcemia. The dose employed is about onetenth the amount used for plicamycin’s cytotoxic action.
1-46. The answer is a. (Braunwald, p 1975.) The first choice in testing in
this patient is a pregnancy test. If her prolactin level was measured without
a pregnancy test, an elevation of prolactin could be wrongly considered
primary rather than due to pregnancy. The other tests of LH, estradiol,
progesterone are not first choices in the evaluation of amenorrhea.
1-47. The answer is b. (Moore & Dalley, pp 339–341, 418–423.) The
indicated line represents the sacroiliac joint. These structures are seen bilaterally between the alae of the sacrum and the ilia. The sacroiliac ligaments
might have been sprained by the trauma of the fall. The pathway for spinal
nerves is through foramina of the sacrum, not through long bony canals.
Similarly, the pathway for the gluteal arteries is through the greater sciatic
foramen between the ilium and the sacrum. However, the bones are not
contiguous at that level.
1-48. The answer is c. (Hardman, p 527. Katzung, p 516.) Naloxone is a
pure opioid antagonist at the µ, κ, and δ receptors. µ-receptor stimulation
causes analgesia, euphoria, decreased gastrointestinal (GI) activity, miosis,
and respiratory depression. κ-receptor stimulation causes analgesia, dysphoria, and psychotomimetic effects. δ-receptor stimulation is not fully
understood in humans, but is associated with analgesia and antinociception
for thermal stimuli.
1-49. The answer is b. (Cotran, pp 619–621.) Paroxysmal nocturnal
hemoglobinuria (PNH) is an acquired clonal stem cell disorder that is characterized by abnormal red cells, granulocytes, and platelets. The red blood
cells (RBCs) are abnormally sensitive to the lytic activity of complement
due to a deficiency of glycosyl phosphatidyl inositol (GPI) linked proteins,
namely decay-accelerating factor (DAF, or CD 55), membrane inhibitor of
reactive lysis (CD55), or CD59 (a C8 binding protein). Complement is normally activated by acidotic states, such as occur with exercise or sleep. In
patients with PNH, the acidotic condition that develops during sleep
(which is usually at night) causes hemolysis of red blood cells and results
Block 1
Answers
199
in red urine in the morning. The erythrocytes of these patients lyse in vitro
with acid (Ham’s test) or sucrose (sucrose lysis test). Complications of PNH
include the development of frequent thromboses, particularly of the
hepatic, portal, or cerebral veins. Since PNH is a clonal stem cell disorder,
patients are at an increased risk of developing aplastic anemia or acute
leukemia.
The autoimmune hemolytic anemias are important causes of acute anemia in a wide variety of clinical states and can be separated into two main
types: those secondary to “warm” antibodies and those reactive at cold temperatures. Warm-antibody autoimmune hemolytic anemias react at 37°C
in vitro, are composed of IgG, and do not fix complement. They are found
in patients with malignant tumors, especially leukemia-lymphoma; with use
of such drugs as α-methyldopa; and in the autoimmune diseases, especially
lupus erythematosus. Cold-antibody autoimmune hemolytic anemia reacts
at 4 to 6°C, fixes complement, is of the IgM type, and is classically associated with Mycoplasma pneumonitis (pleuropneumonia-like organisms).
These antibodies are termed cold agglutinins and may reach extremely high
titers and cause intravascular red cell agglutination.
1-50. The answer is c. (Sierles, pp 185–187. Ebert, pp 268–270.) Many
psychiatric disorders manifest evidence of brain dysfunction. Evidence of
such brain dysfunction has been found in 50% or more of patients with
schizophrenia. For example, a neurologic examination will demonstrate
soft signs (e.g., grasp reflex, rooting reflex, motor impersistence) in 70% of
adult schizophrenics; 75% (whether ill or recovered) will also demonstrate
abnormalities in eye pursuit; 75% will have moderate-to-severe bilateral
impairment on neuropsychological tests; and 50% will have nonspecific
abnormalities on the EEG. Also, 50% will have some cortical atrophy and
ventricular enlargement on imaging tests. The lactate infusion test induces
panic behavior in 80% of patients with panic disorder, but not in patients
with schizophrenia.
This page intentionally left blank.
BLOCK 2
Answers
2-1. The answer is e. (Rhoades, pp 364–368.) Interstitial lung disease is a
restrictive-type lung disease in which all the lung volumes, including VC,
FRC, and RV, are reduced. The decrease in lung volumes is caused by a
decrease in lung compliance. The low compliance produces a high recoil
force so that a higher than normal fraction of the forced vital capacity
(FEV1/FVC) can be exhaled during expiration. The normal pH is consistent
with a normal alveolar ventilation. Because lung compliance is reduced, the
normal alveolar ventilation is maintained with a breathing pattern consisting of a high rate and a low volume.
2-2. The answer is c. (Braunwald, p 1984.) The patient has a common
presentation for secondary hypogonadism. The large tumor is inhibiting
LH secretion with consequently low testosterone secretion. No other pattern fits this clinical presentation.
2-3. The answer is d. ( Moore & Dalley, p 395.) The ischioanal fossa is a
fat-filled space that extends from below the levator ani muscle (puborectalis, pubococcygeus, and iliococcygeus muscles). It also extends anteriorly in the area between the pelvic diaphragm (superiorly) and the
urogenital diaphragm (inferiorly). It cannot extend superiorly above the
pelvic diaphragm and, therefore, cannot extend superiorly anterior to the
sacrum.
2-4. The answer is b. (Hardman, p 1062.) Sulfonamides should not be
used in pregnant women who are at term because of their ability to cross
the placenta and enter the fetus in concentrations sufficient to produce
toxic effects. Sulfonamides should also not be given to neonates, especially
premature infants, because they compete with bilirubin for serum albumin
binding, resulting in increased levels of free bilirubin, which cause kernicterus.
201
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
202
Clinical Vignettes for the USMLE Step 1
2-5. The answer is b. (Cotran, p 1114.) Inflammatory breast carcinoma is
often misunderstood because of the qualifying adjective inflammatory. The
term does not refer to the presence of inflammatory cells, abscess, or any special histologic type of breast carcinoma; rather, it refers to more of a clinical
phenomenon, in that the breast is swollen, erythematous, and indurated and
demonstrates a marked increase in warmth. These changes are caused by
widespread lymphatic and vascular permeation within the breast itself and in
the deep dermis of the overlying skin by breast carcinoma cells. The clinical
induration and erythema are presumably related to lymphatic-vascular
blockage by tumor cells; if present, these findings mean a worse prognosis.
2-6. The answer is c. (Guyton, pp 269–273.) Sweat normally contains
about 40 to 60 meq of sodium per liter of fluid. Thus, approximately 100
meq of sodium will be lost from the extracellular fluid during the exercise
period, and when the lost water is replenished, the extracellular fluid will
become hypotonic. The hypotonic extracellular fluid will equilibrate with
the intracellular fluid and make it hypotonic as well. Because the extracellular fluid volume is dependent on the amount of sodium, the loss of
sodium will result in a decreased extracellular fluid volume and an
increased intracellular fluid volume after water is replaced.
2-7. The answer is d. (Katzung, pp 704, 942.) Leuprolide is a peptide that
is related to GnRH or luteinizing hormone–releasing hormone (LHRH). This
agent is used to treat metastatic prostate carcinoma. A hypogonadal state is
produced in the patient from the continuous administration of leuprolide, by
its capacity to inhibit gonadotropin release. Testosterone levels in the body
become significantly reduced.
2-8. The answer is d. (Levinson, pp 243–247.) In a small number of
patients with acute hepatitis B infection, HBsAg can never be detected. In
others, HBsAg becomes negative before the onset of the disease or before
the end of the clinical illness. In such patients with acute hepatitis, hepatitis B virus infection may only be established by the presence of antihepatitis B core IgM (anti-HBc IgM), a rising titer of anti-HBc, or the
subsequent appearance of anti-HBsAg.
2-9. The answer is c. (Hardman, p 666.) Inhalation therapy minimizes
systemic effects of steroids. Of the agents listed, beclomethasone is the only
one delivered by metered-dose inhaler (MDI).
Block 2
Answers
203
2-10. The answer is b. (McPhee, p 7.) Duchenne’s muscular dystrophy is
an X-linked recessive disorder. The patient’s mother carries one copy of the
recessive gene. It is not expressed in the patient’s sisters who may also carry
one copy of the recessive gene. Because women possess two X chromosomes, the terms X-linked dominant and X-linked recessive apply only to
women. Men, because they possess only one X chromosome, will likely
express the full phenotype irrespective of whether the mutation is a dominant or recessive allele in women.
2-11. The answer is c. (Cotran, p 587.) Accumulations of excess fluid
within the pericardial cavity are called pericardial effusions. The sudden
filling of the pericardial space with fluid is called pericardial tamponade.
The three classic signs of pericardial tamponade, called Beck’s triad,
include hypotension, elevated jugular pressure, and muffled heart sounds.
The latter is due to the damping effect of the pericardial fluid on the heart
sounds. Some patients may also demonstrate a decrease in systemic pressure with inspiration, which is called paradoxic pulse. The decrease in cardiac output produces dyspnea, shortness of breath, and hypotension.
Decreased atrial filling results in elevated jugular venous pressure. There
are several types of pericardial effusions. Serous pericardial effusions are
caused most often by congestive heart failure, but they can also be caused
by renal disease that produces uremia. Serosanguinous effusions are caused
by trauma and cardiopulmonary resuscitation (CPR). Chylous effusions are
caused by lymphatic obstruction, while cholesterol effusions are seen in
patients with myxedema, which is caused by hypothyroidism. Hemopericardium (blood in the pericardial cavity) is most commonly caused by the
rupture of a myocardial infarction.
2-12. The answer is b. (Levinson, pp 218–219.) Adenovirus type 8 is
associated with epidemic keratoconjunctivitis, while adenovirus types 3
and 4 are often associated with “swimming pool conjunctivitis.” There are
also reports of nosocomial conjunctivitis with adenovirus. Herpes simplex
virus can infect the conjunctiva and is among the most common causes of
blindness in North America and Europe.
2-13. The answer is d. (Howard, pp 322, 325–328.) Food poisoning with
E. coli 0157/H7 causes hemorrhagic colitis; it is often seen after eating beef
hamburgers. The same organism also causes a hemorrhagic uremic syndrome. The toxin, called Shiga-like toxin, can be demonstrated in Vero cells,
204
Clinical Vignettes for the USMLE Step 1
but the cytotoxicity must be neutralized with specific antiserum. With the
exception of sorbitol fermentation, there is nothing biochemically distinctive about these organisms.
2-14. The answer is e. (Moore & Dalley, pp 300, 347–348.) The obturator
nerve runs on the lateral surface of the pelvic wall and exits the pelvis
through a canal in the obturator membrane. It innervates the adductor muscles of the medial thigh (a. magnus, a. longus, a. brevis, pectineus, and gracilis). The pudendal nerve exits the pelvic cavity via the greater sciatic
foramen and enters the perineum via the lesser sciatic foramen. It innervates
the perineal muscles and the skin of the genitalia. The genitofemoral nerve
supplies skin over the femoral triangle and scrotum/labia majora. The superior gluteal nerve innervates the gluteus medius and gluteus minimus,
which are powerful abductors of the thigh. The femoral nerve innervates the
quadriceps muscles, which extend the leg at the knee joint.
2-15. The answer is a. (Baum, pp 116–121.) Having some sense of control over a stressful situation is an important factor in coping with stress
and reducing the physiologic reactions to stress. In situations that are
uncontrollable, unpredictable, inescapable, or uncertain, the levels of corticosteroids and catecholamines are increased. Furthermore, corticosteroid
levels decline more slowly after the termination of an uncontrollable or
inescapable stress. Unpredictable shock with no control has also produced
an increased incidence of gastric ulceration in animals. In stressful occupational situations, those workers whose jobs are self-paced show fewer
symptoms of stress and less catecholamine excretion than those whose jobs
are machine-paced. Thus, the potential danger of sustained higher levels of
physiologic reactions to stress is reduced by the person’s having some level
of control. Situations involving uncertainty also involve an increase in the
excretion of epinephrine, norepinephrine, and cortisol.
2-16. The answer is b. (Levinson, pp 306–307.) One of the leading causes
of death among AIDS patients is central nervous system toxoplasmosis. It
is thought that Toxoplasma infection is a result of reactivation of old or preexisting toxoplasmosis. Occasionally, the infection may be acquired by needle sharing. Because the disease is a reactivation of old or preexisting
toxoplasmosis, routine quantitative tests for IgM antibody are usually negative and IgG titers are low (≤1:256, IFA). More sophisticated methods,
such as IgM capture or IgG avidity, may reveal an acute response.
Block 2
Answers
205
2-17. The answer is a. (Murray, pp 48–73. Scriver, pp 4571–4636. Sack,
pp 3–17. Wilson, pp 101–120.) The woman would exhibit respiratory acidosis due to shortness of breath and decreased efficiency of gas exchange
in the lungs. Emphysema involves dilated and dysfunctional alveoli from
alveolar tissue damage, usually secondary to cigarette smoking. The
hypoxia leads to tissue deoxygenation and acidosis, exacerbated by the
hypercarbia (CO2 accumulation) that distinguishes respiratory acidosis
(higher bicarbonate than expected) from metabolic acidosis (very low
bicarbonate, usually with low PCO2 due to compensatory hyperventilation). Choice a shows the only set of values indicating acidosis (pH lower
than 7.4), hypoxia (PO2 lower than 95), and hypercarbia (PCO2 greater
than 44).
The tetrameric structure of hemoglobin allows cooperative binding of
oxygen in that binding of oxygen to the heme molecule of the first subunit
facilitates binding to the other three. This enhanced binding is due to allosteric changes of the hemoglobin molecule, accounting for its S-shaped oxygen saturation curve as compared with that of myoglobin. At the lower
oxygen saturations in peripheral tissues (PO2 30 to 40), hemoglobin releases
much more oxygen (up to 50% desaturated) than myoglobin with its single
polypeptide structure. The amount of oxygen released (and CO2 absorbed
as carboxyhemoglobin) is further increased by the Bohr effect—increasing
hydrogen ion (H+) concentration (lowering pH) and increasing CO2 partial
pressure (PCO2) shift the sigmoidal-shaped oxygen binding curve for hemoglobin further to the right.
2-18. The answer is c. (Cotran, pp 576–577.) Plaques or vegetations are
found in characteristic locations within the heart in several different disorders. Vegetations can occur in acute rheumatic fever as small masses found
in a row along the lines of closure of the valves. In contrast, the vegetations
of infective endocarditis are large, irregular masses that extend beyond the
valves onto the chordae. Nonbacterial thrombotic (marantic) endocarditis,
which is associated with prolonged debilitating diseases and cachexia, may
produce one or two small, sterile vegetations at the line of valve closure. In
patients with systemic lupus erythematosus, medium-sized vegetations
(Libman-Sacks endocarditis) may occur on either or both sides of the valve
leaflets, typically on the mitral valve and the tricuspid valve. The development of Libman-Sacks endocarditis is associated with the presence of the
lupus anticoagulant (antiphospholipid syndrome), an antibody that makes
platelets “sticky” and increases the chance of thrombosis.
206
Clinical Vignettes for the USMLE Step 1
2-19. The answer is c. (Hardman, pp 632–633.) Nausea, vomiting,
abdominal pain, and diarrhea are early signs of the severe liver toxicity
caused by high levels of acetaminophen; other symptoms of acetaminophen toxicity include dizziness, excitement, and disorientation.
N-acetyl-L-cysteine is the appropriate treatment for acetaminophen overdose.
2-20. The answer is d. (Murray, pp 123–148. Scriver, pp 2367–2424. Sack,
pp 159–175. Wilson, pp 287–317.) All of the poisons shown affect either
electron transport or oxidative phosphorylation. Dinitrophenol is unique
in that it disconnects the ordinarily tight coupling of electron transport and
phosphorylation. In its presence, electron transport continues normally
with no oxidative phosphorylation occurring. Instead, heat energy is generated. The same principle is utilized in a well-controlled way by brown fat
to generate heat in newborn humans and cold-adapted mammals. The biological uncoupler in brown fat is a protein called thermogenin. Barbiturates, the antibiotic piericidin A, the fish poison rotenone, dimercaprol,
and cyanide all act by inhibiting the electron transport chain at some point.
2-21. The answer is b. (McKenzie, p 281. Junqueira, pp 335, 341. Kumar,
pp 398–402, Braunwald, p 1455.) The patient suffers from emphysema, in
which neutrophils enter the lung parenchyma and secrete elevated levels of
elastase, leading to the destruction of the bronchiolar and alveolar septal
elastic tissue support. The destruction of the elasticity in emphysema leads
to diminished breath sounds. This is coupled with faint high-pitched
rhonchi at the end of expiration and a hyperresonant percussion note. The
rhonchi are adventitious (not normally present) sounds that may be high
pitched, generally because of bronchospasm, or low pitched, generally
because of the presence of airway secretions. Emphysema is a disease characterized by parenchymal tissue destruction and, therefore, is not associated with adventitious breath sounds. However, because most emphysema
is due to cigarette smoking, there is almost always some degree of chronic
bronchitis, and therefore, rhonchi can be auscultated.
There are genetic and environmental causes of emphysema. The environmental causes include smoking and air pollution, whereas deficiency
in α1-antitrypsin (antiprotease) activity is the genetic cause of the disease.
The balance between normal elastase-elastin production and proteaseantiprotease activity is altered in emphysema. Persons with a deficiency in
Block 2
Answers
207
α1-antitrypsin activity lack sufficient antiprotease activity to counteract neutrophil-derived elastase. When there is an increase in the entry and activation of neutrophils in the alveolar space, more elastase is released, and
elastic structures are destroyed. In smoking there is an increase in the number of neutrophils and macrophages in alveoli and increased elastase activity from neutrophils and macrophages. These changes are coupled with a
decrease in antielastase activity because of oxidants in cigarette smoke and
antioxidants released from the increased numbers of neutrophils. The
increased protease activity causes breakdown of the alveolar walls and dissolution of elastin in the bronchiolar walls. The loss of tethering of the bronchioles to the lung parenchyma leads to their collapse. The bronchioles,
unlike the trachea and bronchi, do not contain hyaline cartilage. A relatively
thick layer of smooth muscle is found in the bronchioles, but the bronchioles are tethered to the lung parenchyma by elastic tissue, which plays a key
role in the stretch and recoil of the lungs during inhalation and exhalation.
2-22. The answer is a. (Plomin, pp 188–192.) Twin studies have consistently shown a strong genetic effect for the heritability of attention deficit
hyperactivity disorder (ADHD). The findings show the heritability to be
about 70%. The genetic component for ADHD is stronger than for most
other psychopathologies except autism. Adoption studies also support the
high heritability of ADHD.
The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV)
defines ADHD as a disorder in which a child is very restless, has a poor
attention span, and acts impulsively. Prevalence is about 4% of elementary
school children, with boys outnumbering girls. European psychiatrists put
more emphasis on the pervasive hyperactivity and early onset, but not on
high anxiety. One problem with the DSM-IV grouping ADHD with disruptive behavior disorder is that disruptive behavior disorder shows only
modest genetic influence and doesn’t involve hyperactivity or inattentiveness. Nevertheless, there is some overlap between hyperactivity and conduct disorder symptoms, e.g., early onset hyperactivity has an increased
risk for the later onset of conduct problems. However, the comorbidity rate
has diminished for the “pure” ADHD probands who do not show symptoms of conduct disorder.
2-23. The answer is d. (Cotran, pp 148, 1254–1255. Champe, 348–349.)
Purine synthesis involves adding carbons and nitrogens to ribose
208
Clinical Vignettes for the USMLE Step 1
5-phosphate (R5P), which is a product of the hexose monophosphate
(HMP) shunt. R5P is then converted to ribose phosphate pyrophosphate
(RPPP), which is subsequently converted to 5′-phosphoribosylamine, the
latter step being the committed step in purine nucleotide biosynthesis.
Through a series of steps RPPP is converted to inosine 5′-monophosphate
(IMP). Several of these biochemical steps involve transferring methyl
groups from folate. This is important because folate analogues, such as
methotrexate, inhibit DNA synthesis, especially in rapidly growing tumor
cells, by inhibiting purine synthesis. Finally IMP is converted into either
AMP or GMP. These last biochemical steps are also connected to biochemical reactions that involve adenosine deaminase, an enzyme that is
deficient in individuals with the autosomal recessive form of SCID, and
hypoxanthine-guanine phosphoribosyl transferase (HGPRT), an enzyme
of the purine salvage pathway for recycling guanine and hypoxanthine
that is deficient in individuals with the X-linked recessive disorder LeschNyhan syndrome. This disorder is characterized by excess uric acid production, which may produce symptoms of gout, mental retardation, spasticity,
self-mutilation, and aggressive behavior. In contrast, a deficiency of homogentisic oxidase, which is involved in the conversion of homogentisic acid
to methylacetoacetate, is associated with alkaptonuria. Abnormal degradation of galactocerebroside is seen in Krabbe’s disease, while abnormal
breakdown of branched-chain amino acids is seen in maple syrup urine
disease.
2-24. The answer is c. (Murray, pp 123–148. Scriver, pp 2367–2424. Sack,
pp 159–175. Wilson, pp 287–317.) The most likely cause of the symptoms
observed is carnitine deficiency. Under normal circumstances, long-chain
fatty acids coming into muscle cells are activated as acyl coenzyme A and
transported as acyl carnitine across the inner mitochondrial membrane
into the matrix. A deficiency in carnitine, which is normally synthesized in
the liver, can be genetic; but it is also observed in preterm babies with liver
problems and dialysis patients. Blockage of the transport of long-chain
fatty acids into mitochondria not only deprives the patient of energy production, but also disrupts the structure of the muscle cell with the accumulation of lipid droplets. Oral dietary supplementation usually can effect
a cure. Deficiencies in the carnitine acyltransferase enzymes I and II can
cause similar symptoms.
Block 2
Answers
209
2-25. The answer is e. (Murray, pp 1406–1412.) Cyclosporiasis is a newly
recognized food- and water-borne infectious disease associated with eating
contaminated berries imported from some Central American countries.
Cyclospora are moderately acid-fast but twice the size of Cryptosporidium.
Patients usually have frequent diarrhea for up to 3 weeks and usually suffer
only malaise and fatigue. The disease is self-limiting, but relapses can occur.
2-26. The answer is g. (Katzung, pp 170–171.) Sodium nitroprusside
reduces blood pressure by dilating both arterial and venous vessels. It most
likely acts by releasing nitric oxide, which reacts with guanylyl cyclase. This
results in an increase in intracellular cyclic guanosine 5′-monophosphate
[cyclic GMP (cGMP)], a vascular smooth-muscle relaxant. Another possible
explanation for increased intracellular levels of GMP is the direct action of
sodium nitroprusside on guanylyl cyclase. Sodium nitroprusside is a useful
agent in the treatment of hypertensive emergencies because of its rapid
onset and short duration of action.
2-27. The answer is a. (Cotran, p 1210.) Fungal infections of the skin
can be classified into superficial mycoses, cutaneous mycoses, and subcutaneous mycoses. The superficial mycoses are characterized by infection of
the superficial layers of the skin. The most common type is pityriasis versicolor (tinea versicolor), an infection of the upper trunk that is caused by M.
furfur (Pityrosporum orbiculare). Clinically, there are multiple groups of
macules (discolorations) with a fine peripheral scale. These macules are
hyperpigmented (dark) in white-skinned races but hypopigmented (light)
in dark-skinned races. These areas fluoresce yellow under a Wood’s lamp.
Potassium hydroxide (KOH) is used to identify fungal infections from
scrapings of the skin. The KOH dissolves the keratin, and then the mycelial
fungi can be seen. With tinea versicolor, KOH examination reveals a characteristic “spaghetti and meatball” appearance. The fragments of hyphae
are the “spaghetti,” while the round yeast cells are the “meatballs.” Different types of tinea include tinea capitis, tinea corporis, tinea pedis (athlete’s
foot), and tinea versicolor.
2-28. The answer is e. (Murray, pp 307–346. Scriver, pp 1667–1724. Sack,
pp 121–138. Wilson, pp 287–317.) Collagen has an unusual amino acid
composition in that approximately one-third of collagen molecules are
210
Clinical Vignettes for the USMLE Step 1
glycine. The amino acid proline is also present in a much greater amount
than in other proteins. In addition, two somewhat unusual amino acids,
4-hydroxyproline and 5-hydroxylysine, are found in collagen. Hydroxyproline and hydroxylysine per se are not incorporated during the synthesis
of collagen. Proline and lysine are hydroxylated by specific hydroxylases
after collagen is synthesized. A reducing agent such as ascorbate (vitamin
C) is needed for the hydroxylation reaction to occur. In its absence, the disease known as scurvy occurs. Only proline or lysine residues located on the
amino side of glycine residues are hydroxylated. The hydroxylysine residues of collagen are important sites of glycosylation of disaccharides of glucose and galactose.
2-29. The answer is a. (April, pp 133, 140.) The deep incisure in the inferior border of the pedicle ensures that the spinal nerve associated with that
vertebra will exit through the intervertebral foramen well above the intervertebral disk so that it will not be affected by a herniation at that level.
However, a posterolateral herniation (the usual direction) will impinge on
the next lower nerve as it courses toward its associated intervertebral foramen. In this case, pain was distributed along the medial side of the leg and
foot as far as the great toe—the distribution of the saphenous branch of the
femoral nerve (L4). Herniation of the third lumbar intervertebral disk
between vertebral bodies L3–L4 would affect nerve L4.
2-30. The answer is c. (Hardman, p 546.) Pentazocine is a mixed agonistantagonist of opioid receptors. When a partial agonist, such as pentazocine,
displaces a full agonist, such as methadone, the receptor is less activated; this
leads to withdrawal syndrome in an opioid-dependent person.
2-31. The answer is c. (Cotran, p 1079–1080.) Ectopic pregnancy is a
potentially life-threatening condition if it is not treated by removal before
rupture and hemorrhage with fatal exsanguination. The most common
location for extrauterine implantation is the fallopian tube (more than 85%
of cases), with rare implantation in the ovary or abdomen. If the tubal
implantation has existed for 1 to 4 weeks, the β-hCG test result is likely to
be negative; thus a negative result does not exclude pregnancy. It is always
worthwhile to repeat a laboratory test when the result is unexpected. Tubal
pregnancy is not uncommon and should always be considered if endometrial samples suggest gestational change without chorionic villi.
Block 2
Answers
211
2-32. The answer is b. (Plomin, pp 26–37.) Complex behavioral traits
such as schizophrenia, which may vary widely in nature from person to
person, are considered to involve anomalies at more than one gene locus.
The science of behavior genetics deals with the quantitative analysis of
these polygenic traits. The results of a great variety of investigations now
favor the view that schizophrenia is a genetically determined disorder, but
it also may be substantially affected by environmental influences.
2-33. The answer is c. (Moore & Dalley, p 345.) The puborectalis, pubococcygeus, and iliococcygeus comprise the levator ani, the main muscular
component of the pelvic floor. The pubococcygeus is the part of the levator
ani most frequently damaged during parturition. Because the pubococcygeus surrounds and supports the neck of the bladder and the proximal urethra, urinary leakage is a common result, particularly during
increased abdominopelvic pressure, e.g., during coughing. Damage to the
puborectalis would result in fecal incontinence under similar situations.
Both the obturator internus muscle and the piriformis are parts of the lateral wall of the pelvis and assist in lateral rotation of the thigh.
2-34. The answer is a. (Braunwald, pp 618–619.) Hypercalcemia of
malignancy is the most common paraneoplastic syndrome. It accounts for
about 40% of all hypercalcemia. The signs and symptoms of hypercalcemia
include bone pain, irritability, weakness, fatigue, constipation, nausea, and
vomiting, as this patient manifests. Symptoms begin at a serum calcium of
about 2.6 mmol/L. Hypercalcemia of malignancy is common in cancers
with squamous cell histology.
2-35. The answer is c. (Murray, pp 48–62. Scriver, pp 3–45. Sack, pp 1–3.
Wilson, pp 101–120.) Protein electrophoresis is an important laboratory
technique for investigating red cell proteins such as hemoglobin or plasma
proteins such as the immunoglobulins. The proteins are dissolved in a
buffer of low pH where the amino groups of amino acid side chains are
positively charged, causing most proteins to migrate toward the negative
electrode (anode). Red cell hemolysates are used for hemoglobin electrophoresis, plasma (blood supernatant with unhemolyzed red cells removed)
for plasma proteins. Serum (blood supernatant after clotting) would not
contain red cells but would contain many blood enzymes and proteins. In
sickle cell anemia, the hemoglobin S contains a valine substitution for the
212
Clinical Vignettes for the USMLE Step 1
glutamic acid at position 6 in hemoglobin A. Hemoglobin S thus loses two
negative charges (loss of a glutamic acid carboxyl group on each of two
β-globin chains) compared to hemoglobin A. Hemoglobin S is thus more
positively charged and migrates more rapidly toward the anode than hemoglobin A. Lane B must represent the heterozygote with sickle cell trait
(hemoglobins S and A), establishing lane A as the normal and lane D as the
sickle cell anemia sample. The hemoglobin in lane C migrates differently
from normal and hemoglobin S, as would befit an abnormal hemoglobin
that is different from S.
2-36. The answer is d. (Katzung, pp 779–780.) Erythromycin is safe to
use in pregnancy and is effective against Chlamydia. Levofloxacin is contraindicated in pregnancy because animal studies have identified that cartilage erosion can occur during growth. Chlamydia are not sensitive to
gentamycin, however, it probably should not be used in pregnancy
because of potential nephro- and ototoxicity. Tetracycline may cause tooth
enamel dysplasia and problems with bone during fetal development.
Sulfamethoxazole-trimethoprim has severe consequences, particularly in
the newborn, because it displaces bilirubin from albumin, which is then
deposited in the brain causing a condition referred to as kernicterus.
2-37. The answer is c. (Gutyon, pp 360–363.) Increasing bicarbonate
concentration in the plasma results in a metabolic alkalosis. To compensate
for the alkalosis, the respiratory system decreases alveolar ventilation.
Therefore, an increase in plasma bicarbonate and arteriolar PCO2 is characteristic of metabolic alkalosis. The respiratory system will not allow arteriolar PCO2 to increase much above 50 mmHg, so respiratory compensation
for a metabolic alkalosis is limited. A similar limitation is not present when
metabolic acidosis occurs, so respiratory compensation can reduce arteriolar PCO2 to below 10 mmHg. Although NaHCO3− ingestion does not typically cause metabolic alkalosis, its use is not recommended because
alkalosis may occur and because it may result in Na+ retention.
2-38. The answer is e. (Cotran, pp 1039–1040, 1065.) Pelvic inflammatory disease (PID) is a common disorder caused by infection with either
gonococci (the most common cause), chlamydiae, or enteric bacteria.
Gonococcal infection, seen microscopically as gram-negative intracellular
Block 2
Answers
213
diplococci, begins in the Bartholin’s glands and then spreads upward to
involve the fallopian tubes and tuboovarian regions. This produces PID,
which is characterized by pelvic pain, fever, adnexal tenderness, and pain
when the cervix is manipulated. Complications of PID include peritonitis from rupture of a tuboovarian abscess, infertility, and intestinal
obstruction.
2-39. The answer is d. (Murray, pp 48–62. Scriver, pp 3–45. Sack, pp 1–3.
Wilson, pp 101–120.) Collagen peptides assemble into helical tertiary structures that form quaternary triple helices. The triple helices in turn assemble end to end to form collagen fibrils that are essential for connective
tissue strength. Over 15 types of collagen contribute to the connective tissue of various organs, including the contribution of type I collagen to eyes,
bones, and skin. The fact that only one of two α2 alleles is normal in this
case implies that a mutant α2 allele could be responsible for the disease
(even if the α2 locus is on the X chromosome, since the baby is female with
two X chromosomes). The mutant α2 collagen peptide would be incorporated into half of the type I collagen triple helices, causing a 50% reduction
in normal type I collagen. (A mutant α1 collagen peptide would distort
75% of the molecules since two α1 peptides go into each triple helix). The
ability of one abnormal collagen peptide allele to alter triple helix structure
with subsequent degradation is well documented and colorfully named
protein suicide or, more properly, a dominant-negative mutation.
2-40. The answer is a. (Levinson, pp 212–213, 218–219, 219–220, 214–
215.) Varicella-zoster virus is a herpesvirus. Chickenpox is a highly contagious disease of childhood that occurs in the late winter and early spring. It
is characterized by a generalized vesicular eruption with relatively insignificant systemic manifestations.
Adenovirus has been associated with adult respiratory disease among
newly enlisted military troops. Crowded conditions and strenuous exercise
may account for the severe infections seen in this otherwise healthy group.
Papillomavirus is one of two members of the family Papovaviridae,
which includes viruses that produce human warts. These viruses are hostspecific and produce benign epithelial tumors that vary in location and
clinical appearance. The warts usually occur in children and young adults
and are limited to the skin and mucous membranes.
214
Clinical Vignettes for the USMLE Step 1
Rotavirus is worldwide in distribution and has been implicated as the
major etiologic agent of infantile gastroenteritis. Infection with this virus
varies in its clinical presentation from asymptomatic infection to a relatively mild diarrhea to a severe and sometimes fatal dehydration. The exact
mode of transmission of this infectious agent is not known. Because of
severe side effects, the rotavirus vaccine has been recalled and is temporarily unavailable.
Infectious mononucleosis caused by cytomegalovirus (CMV) is clinically difficult to distinguish from that caused by Epstein-Barr virus. Lymphocytosis is usually present with an abundance of atypical lymphocytes.
CMV-induced mononucleosis should be considered in any case of
mononucleosis that is heterophil-negative and in patients with fever of
unknown origin.
2-41. The answer is c. (Braunwald, pp 348, 656, 658, 1574, 1590.
McKenzie, p 223. Junqueira, pp 234–237.) The most likely cause of the
anemia is renal failure, leading to decreased production of the kidney–
derived red blood cell growth factor, erythropoietin. In the initial stages
of renal failure the kidneys will increase their production of erythropoietin, but as renal damage continues the cells that produce this factor are
destroyed. Therefore, there are initially increased levels of reticulocytes
(immature red blood cells) in the bloodstream, but as in the anemia of
renal disease, low production of reticulocytes is a hallmark of the disease.
Although the patient may have decreased estrogen levels, estrogen
decreases hematocrit. Also, women who are pregnant (third trimester)
can have slightly decreased hematocrits [37 ⫾ 6 (third trimester pregnant
women) vs. 40 ⫾ 6 (adult women) and 42 ⫾ 6 (postmenopausal women)].
Administration of recombinant erythropoietin (EPO) is the preferred
treatment for anemia caused by advanced renal disease. Generally, EPO is
administered if the hematocrit is less than 30% and whether the patient
is on dialysis.
Erythropoietin is synthesized by the peritubular (interstitial) cells of
the kidney cortex, stimulates the differentiation of cells from the erythrocyte colony–forming units (E-CFUs) and stimulates the differentiation and
release of reticulocytes from the bone marrow. Colony-forming units
(CFUs) are distinct cell lineages derived from pluripotential stem cells in
the bone marrow.
Block 2
Answers
215
2-42. The answer is a. (Hardman, pp 1660–1661.) Arsenic is an active
constituent of fungicides, herbicides, and pesticides. Symptoms of acute
toxicity include tightness in the throat, difficulty in swallowing, and stomach pains. Projectile vomiting and severe diarrhea can lead to hypovolemic
shock and death. Chronic poisoning may cause peripheral neuritis, anemia, skin keratosis, and capillary dilation leading to hypotension. Dimercaprol is the primary agent used in the treatment of arsenic poisoning.
2-43. The answer is a. (Raoult, pp 284–285.) Dengue (breakbone fever)
is caused by a group B togavirus that is transmitted by mosquitoes. The
clinical syndrome usually consists of a mild systemic disease characterized
by severe joint and muscle pain, headache, fever, lymphadenopathy, and a
maculopapular rash. Hemorrhagic dengue, a more severe syndrome, may
be prominent during some epidemics; shock and occasionally death result.
2-44. The answer is d. (Hardman, p 906.) Cimetidine slows the metabolism of Ca channel blockers, which are substrates for hepatic mixed-function
oxidases. Inhibition of cytochrome P450 activity is peculiar to cimetidine
and is not a mechanism of action of other histamine 2 (H2) blockers.
2-45. The answer is a. (Kandel, pp 36–60.) Humans have a number of
simple behaviors that resemble the fixed action patterns of lower animals.
Such emotional expressions as the startle response and smiling are stereotyped sequences of movements. In human infants smiling appears to be
under the control of a specific sign stimulus. Studies show that the smiling
response is not triggered by the face as a whole, but rather by certain specific features. For example, the eyes are of particular importance as a sign
stimulus, and as the child matures, other features of the face become
important. The brow flash response (rapid raising and dropping of eyebrows) is a stereotyped response present in widely different cultures and is
used as part of a greeting response. A complex set of human behaviors that
is universal in emotional expression across cultures and that involves a
stereotyped sequence of fixed action patterns includes the facial expressions of anger, fear, disgust, and joy. As an example, babies who are born
blind can have emotional facial expressions that appear normal. While
apprehension may include some of the responses also found in fear, it does
not include as many, nor are the responses as severe.
216
Clinical Vignettes for the USMLE Step 1
2-46. The answer is b. (Cotran, pp 564–566. Abenhaim, pp 609–616. Connolly, pp 581–588.) Hypertensive heart disease (HHD) can be divided into
systemic HHD and pulmonary HHD. Systemic HHD is the result of systemic hypertension, which causes left ventricular (LV) hypertrophy. There
is by definition no other cardiac disease present that could cause LV hypertrophy, such as aortic stenosis. Hypertension is a pressure overload on the
heart, and as such it causes concentric LV hypertrophy without dilation. In
contrast, eccentric hypertrophy is the result of volume overload on the
heart. In systemic HHD the LV is stiff, as there is decreased LV compliance.
In a patient with uncontrolled hypertension, LV dilation would indicate LV
failure. Pulmonary HHD indicates right ventricular hypertrophy that is the
result of pulmonary disease. By definition, this type of heart disease is
called cor pulmonale. Pulmonary diseases that can cause cor pulmonale
include diseases of the lung parenchyma, such as chronic obstructive pulmonary disease and interstitial fibrosis, and diseases of the pulmonary vessels, such as multiple pulmonary emboli and pulmonary vascular sclerosis.
The latter has been associated with the use of the combination of diet drugs
fenfluramine and phentermine. (This combination has been referred to as
Fen-Phen.)
2-47. The answer is e. (Braunwald, p 1986.) The suppression of ACTH
is characteristic of adrenal adenoma or carcinoma. A CT scan will evaluate
for the presence of adrenal tumor. Chest CT is useful in ectopic ACTH
secretion. A MRI of the pituitary is useful in pituitary dependent Cushing’s
disease. The ACTH stimulation test and serum ADH are not diagnostic in
this disease.
2-48 and 2-49. The answers are 2-48 c, 2-49 c. (Afifi, pp 133–134.)
The central pathways mediating taste include the following: primary afferent taste fibers associated with taste receptors of cranial nerves VII, IX, and
X synapse in the solitary nucleus. Many fibers from the solitary nucleus
project to the ventral posteromedial nucleus of the thalamus, which, in
turn, project to the ventrolateral aspect of the postcentral gyrus.
2-50. The answer is b. (Kumar, pp 249, 251. Greenspan, pp 320–322. Junqueira, pp 145–148. Braunwald, pp 2201–2204.) The patient suffers from
osteomalacia, a disease related to malnutrition, specifically vitamin D defi-
Block 2
Answers
217
ciency. On the basis of the first bone biopsy in which the tissue was decalcified, one could make a diagnosis of osteoporosis. The second, nondecalcified bone biopsy indicates that osteoid is being formed but is not
undergoing mineralization. This correlates with the low 25-hydroxyvitamin
D levels. Vitamin D replacement and calcium supplementation would be
prescribed for this patient.
This page intentionally left blank.
BLOCK 3
Answers
3-1. The answer is d. (Braunwald, pp 628–629.) Any back pain in a
patient with a known history of carcinoma should be evaluated for the possibility of spinal cord compression. It occurs in 5 to 10% of patients with
cancer. Lung cancer is the most common primary malignancy causing
spinal cord compression. Localized back pain and tenderness are the most
common initial complaints.
3-2. The answer is b. (Braunwald, pp 2041–2042. Moore, Before We are
Born, pp 155, 157. Moore, Developing Human, pp 121–122, 171, 172, 174–175.)
Cells from a patient with the most common form of Klinefelter syndrome
(47,XXY genotype) will have one inactive X chromosome and, therefore,
one Barr body. The formula is the number of Barr bodies equals the number of X chromosomes minus one. Klinefelter syndrome occurs about
1:500 males and is due to meiotic nondisjunction of the chromosomes.
The nondisjunction is more frequent in oogenesis than spermatogenesis,
and increased occurrence is directly proportional to increasing maternal
age. Klinefelter may occur as 47,XXY, 48,XXYY, 48,XXXY, and 49,XXXXY.
A combination of abnormal and normal genotype occurs in mosaic individuals who generally have less severe symptoms. Females have two X
chromosomes, one of maternal and the other of paternal origin. Only one
of the X chromosomes is active in the somatic, diploid cells of the female;
the other X chromosome remains inactive and is visible in appropriately
stained interphase cells as a mass of heterochromatin. Detection of the Barr
body (sex chromatin) has been an efficient method for the determination of
chromosomal sex and abnormalities of X-chromosome number; however, it
is not definitive proof of maleness or femaleness. The genotypic sex of Klinefelter syndrome and XXX individuals would be male and female as determined by the presence or absence of the testis-determining Y chromosome.
In Turner’s syndrome (XO), no Barr bodies would be present. In comparison, “superfemales” (XXX) would possess two inactive X chromosomes (2
219
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
220
Clinical Vignettes for the USMLE Step 1
Barr bodies) and one active X chromosome. Buccal scrapings for Barr body
analysis are being used less—chromosomal analysis is becoming the standard test now.
3-3. The answer is d. (Hardman, pp 1247, 1335.) Leucovorin prevents
methotrexate from inhibiting dihydrofolate reductase and reverses all of its
adverse effects except neurotoxicity.
3-4. The answer is b. (Afifi, pp 82–85.) The medial vestibulospinal tract
arises from the medial vestibular nucleus and descends in the medial longitudinal fasciculus to cervical levels where it controls LMNs, which innervate (flexor) muscles controlling the position of the head. The lateral
vestibulospinal tract facilitates extensor motor neurons of the limbs; the
rubrospinal tract facilitates flexor motor neurons of the limbs; and the
reticulospinal tracts modulate muscle tone of the limbs.
3-5. The answer is a. (Hardman, pp 977–978.) Primaquine is effective
against the extraerythrocytic forms of P. vivax and P. ovale and is thus of
value in a radical cure of malarial infection. It also attacks the sexual forms
of the parasite, rendering them incapable of maturation in the mosquito
and making it valuable in preventing the spread of malarial infection.
3-6. The answer is c. (Cotran, pp 649–650. Chandrasoma, pp 433–443.)
Lymph nodes may be enlarged (lymphadenopathy) secondary to reactive
processes, which can be either acute or chronic. Acute reaction (acute nonspecific lymphadenitis) can result in focal or generalized lymphadenopathy. Focal lymph node enlargement is usually the result of bacterial
infection. Sections from involved lymph nodes reveal infiltration by neutrophils. In contrast, generalized acute lymphadenopathy is usually the
result of viral infections and usually produces a proliferation of reactive T
lymphocytes called T immunoblasts. These reactive T cells tend to have
prominent nucleoli and can be easily mistaken for malignant lymphocytes
or malignant Hodgkin cells.
Reactive processes involving lymph nodes typically involve different
and specific portions of the lymph nodes depending upon the type of cell
that is reacting. For example, reactive B lymphocytes typically result in
hyperplasia of the lymphoid follicles and germinal centers (follicular
hyperplasia). Examples of diseases that are associated with follicular hyper-
Block 3
Answers
221
plasia include chronic inflammation caused by organisms, rheumatoid
arthritis, and AIDS. Lymph nodes from patients with AIDS undergo characteristic changes that begin with follicular hyperplasia with loss of mantle
zones, intrafollicular hemorrhage (“follicle lysis”), and monocytoid B cell
proliferation. Subsequently there is depletion of lymphocytes (CD4+ lymphocytes) in both the follicles and the interfollicular areas. In contrast to
reactive B cell processes, reactive T lymphocytes typically result in hyperplasia involving the T cell areas of the lymph node, namely the interfollicular regions and the paracortex. Examples of clinical situations associated
with a T lymphocyte response include viral infections, vaccinations, use of
some drugs (particularly Dilantin), and systemic lupus erythematosus. The
sinusoidal pattern of reaction involves expansion of the sinuses by benign
macrophages, as seen in reactive proliferations of the mononuclearphagocytic system. Stellate microabscesses (irregular areas composed of
central necrotic cellular and neutrophil debris surrounded by palisading
macrophages) are characteristic of cat-scratch disease, lymphogranuloma
venereum, and tularemia.
3-7. The answer is b. (Ryan, p 505.) Herpes simplex virus causes primary and recurrent disease. The typical skin lesion is a vesicle that contains
virus particles in serous fluid. Giant multinucleated cells are typically
found at the base of the herpesvirus lesion. Encephalitis, which usually
involves the temporal lobe, has a high mortality rate. Severe neurologic
sequelae are seen in surviving patients.
3-8. The answer is a. (Coe, pp 1042–1052. Kumar, pp 673–675. Greenspan,
pp 326–329.) The correct diagnosis is Paget’s disease, also known as osteitis
deformans because of its deforming capabilities (e.g., skull or femoral head
enlargement). In this disease the serum calcium is normal, but there is an
increase in osteoclastic activity (osteolytic lesions and elevated 24-h urine
hydroxyproline) and an increase in osteoblastic activity (elevated osteocalcin and alkaline phosphatase). Patients with Paget’s disease exhibit a
marked increase in osteoid, and the bone actually enlarges. The osteoid is
never normally mineralized in this disease. In this patient, the bone scan
shows significant uptake of labeled bisphosphonates, which are incorporated into newly formed osteoid during bone formation. Her proximal
femur is enlarged and no longer fits properly into the acetabulum, which
results in the hip pain.
222
Clinical Vignettes for the USMLE Step 1
There are a number of useful biochemical markers of bone metabolism.
Osteoclasts synthesize tartrate–resistant acid phosphatase so that increased
osteoclastic activity is reflected in increased serum levels of tartrate–resistant
acid phosphatase. Bone resorption fragments of type I collagen and noncollagenous proteins increase as bone matrix is resorbed. Hydroxyproline is a
good urinary marker of bone metabolism because hydroxyproline is
released and excreted in the urine as collagen is broken down. The presence
of pyridinoline cross-links, which are involved in the bundling of type I collagen, is used for measurement of bone resorption. These cross-links are
released only during degradation of mineralized collagen fibrils as occurs
in bone resorption. Usually, pyridinoline cross-links are measured by
immunoassay over a 24-h period to detect excess bone resorption and collagen breakdown in disorders such as Paget’s disease.
Markers of bone formation include osteocalcin, alkaline phosphatase,
and the extension peptides of type I collagen. Osteocalcin is a vitamin
K–dependent gla (γ-carboxyglutamic acid) protein that is synthesized by
osteoblasts and secreted into the serum in an unchanged state. Serum concentrations of osteocalcin are, therefore, directly related to osteoblastic
activity. It is a more specific marker than the marker alkaline phosphatase,
because other organs, such as the liver and kidney, produce that enzyme.
Radiologic methods such as conventional x-ray can be used to detect
osteoporosis, but only after patients have lost 30 to 50% of their bone
mass. Dual-beam photon absorptiometry allows a much more accurate
diagnosis of loss of bone mass.
3-9. The answer is b. (Moore & Dalley, pp 256–257.) Infectious mononucleosis is a virus-induced illness leading to swollen lymph nodes and
spleen. The splenomegaly is evidenced by the very rounded contours of the
organ. Infectious mononucleosis can exhibit liver involvement; however,
the organ indicated is not the liver but the spleen in the upper left
hypochondrium. The bright organ between it and the vertebra is the left
kidney. The liver is on the opposite side of the abdominal cavity.
3-10. The answer is a. (Guyton, pp 948–949.) Continuous secretion of
progesterone by the corpus luteum is essential for development of the
fetus. During the first trimester, placental production of hCG sustains the
corpus luteum and ensures continued progesterone secretion. By the second trimester, progesterone production by the placenta increases to levels
sufficient to sustain fetal growth and development.
Block 3
Answers
223
3-11. The answer is d. (Cotran, pp 1221–1222.) Osteogenesis imperfecta
(OI), or brittle bone disease, constitutes a group of disorders often inherited as autosomal dominant traits and caused by genetic mutations involving the synthesis of type I collagen, which comprises about 90% of the
osteoid, or bone matrix. Very early perinatal death and multiple fractures
occur in OI type II, which is often autosomal recessive. The major variant
of OI, type I, is compatible with survival; after the perinatal period fractures occur in addition to other signs of defective collagen synthesis such
as thin, translucent, blue scleras; laxity of joint ligaments; deafness from
otosclerosis; and abnormal teeth. A hereditary defect in osteoclastic function with decreased bone resorption and bone overgrowth, which sometimes narrows or obliterates the marrow cavity, is characteristic of
osteopetrosis, or marble bone disease. Osteomalacia is seen in adults due to
vitamin D deficiency, while osteitis deformans is Paget’s disease of bone.
3-12. The answer is a. (Raoult, p 356.) With an acute case of primary
infection by Epstein-Barr virus (EBV), such as infectious mononucleosis,
IgM antibodies to VCA should be present. Antibodies to EBNA should be
absent, as they usually appear 2 to 3 months after onset of illness. Culture
is not clinically useful because it (1) requires freshly fractionated cord
blood lymphocytes, (2) takes 3 to 4 weeks for completion, and (3) is reactive in the majority of seropositive patients.
3-13. The answer is e. (Hardman, p 745.) Vasodilator therapy for CHF
has gained prominence in the past 10 years. The ACE inhibitors, such as
enalapril, are among the best agents for this purpose, although Ca channel
inhibitors and nitroglycerin can also be used. The ACE inhibitors dilate
arterioles and veins (reducing preload), as well as inhibit aldosterone production (reducing blood volume), factors considered beneficial in CHF
therapy. Both β-adrenergic antagonists and ACE inhibitors have been
shown to increase survival in CHF.
3-14. The answer is a. (McPhee, p 148; Braunwald, pp 134–142.) Although various areas of the cerebral cortex are specialized to perform certain functions, the cognitive and behavioral domains (language, memory,
calculation ability, and so forth) are interconnected to both cortical and
subcortical neural networks. Specific deficits identified in a careful neurologic exam will help define which area or network has been damaged.
Aphasia is an abnormality of language. Anomia, the inability to name, is a
224
Clinical Vignettes for the USMLE Step 1
form of aphasia. Apraxia is a complex motor deficit not attributable to
pyramidal, extrapyramidal, cerebellar, or sensory abnormalities.
3-15. The answer is d. (Baum, pp 304–306.) There is an increased interest
in self-control or self-management programs in terms of what individuals can
do for themselves. Many weight loss programs have established that selfreward is the most effective tool during both posttreatment and follow-up.
Self-reward acts as a contingent reinforcement for losing weight. Selfmonitoring is a part of some self-management programs, but is not as effective
as self-reward. Self-control procedures have been applied to other areas, such
as self-management of diabetes where patients can pay attention to specific
adaptive behaviors that they can control. Thus, self-reinforcement becomes a
powerful cognitive-behavioral intervention.
3-16. The answer is b. (Moore & Dalley, pp 775, 821–822.) The patient
has a classic case of carpal tunnel syndrome, in which the median nerve is
compressed as it passes through the carpal tunnel formed by the flexor retinaculum in the wrist. Evidence for involvement of the median nerve is
weakness and atrophy of the thenar muscles (abductor pollicis brevis,
opponens pollicis) and lumbricals 1 to 3. Sensory deficits also follow the
distribution of the median nerve. The median nerve enters the hand, along
with the tendons of the superficial and deep digital flexors, through a tunnel framed by the carpal bones and the overlying flexor retinaculum.
Symptoms are worse in the early morning and in pregnancy because of
fluid retention, resulting in swelling that entraps the median nerve. Flexing
the wrist for an extended period exaggerates the paresthesia (“Phelan’s”
sign) by increasing pressure on the median nerve.
Neither the ulnar nerve, radial nerve, nor radial artery passes through
the carpal tunnel. The ulnar nerve supplies the third and fourth lumbricals
and only the short adductor of the thumb. The radial nerve innervates mostly
long and short extensors of the digits and the dorsal aspect of the hand.
Proper digital nerves lie distal to the carpal tunnel but are only sensory.
3-17. The answer is e. (Hardman, p 72.) Activated charcoal, a fine, black
powder with a high adsorptive capacity, is considered to be a highly valuable
agent in the treatment of many kinds of drug poisoning. Drugs that are well
adsorbed by activated charcoal include primaquine, propoxyphene, dextroamphetamine, chlorpheniramine, phenobarbital, carbamazepine, digoxin,
Block 3
Answers
225
and aspirin. Mineral acids, alkalines, tolbutamide, and other drugs that are
insoluble in acidic aqueous solution are not well adsorbed. Charcoal also
does not bind Ca, lithium (Li), or Fe.
3-18. The answer is d. (Braunwald, pp 1051–1052.) Infection with Coxiella burnetii (or Q fever) represents an occupational hazard of veterinarians. Q fever is characterized by fever, extreme fatigue, and headache, and
about one-fourth of persons with the infection develop thrombocytopenia,
unlike in the other infections. Mycoplasma pneumoniae infection is insidious and causes pneumonia as does Chlamydia pneumoniae infection;
thrombocytopenia is not a characteristic of these infections. Influenza
develops rapidly, in 2 to 3 days from exposure.
3-19. The answer is d. (Sierles, pp 9–11. Wedding, pp 366–377.) A
depressed mood and depressive illnesses are the most common psychosocial reactions of persons with AIDS. A depressive illness can be secondary
to a viral infection of the brain and nervous system or a side effect of drugs
used to treat AIDS, or it can arise from preexisting mood disorders.
Depressed mood and depressive illnesses can also occur from psychosocial
stress generated from such factors as reception of a fatal diagnosis, loss of
confidentiality, stigma of having AIDS, rejection by friends and family, loss
of independence, loss of bowel and bladder control, or loss of occupational
competence. Adaptation is a psychosocial factor that affects depression,
especially in terms of what the illness means to the patient—e.g., the illness
as a challenge, an enemy, a punishment, a weakness, a strategy for life, an
irreparable loss or injury, an incentive to change behavior, or a threat to
coping capacities. Some of the behaviors that can be observed in depressed
moods and illnesses include a sad, apathetic, or anxious mood, loss of selfesteem, guilt, hopeless or helpless feelings, insomnia, loss of appetite, and
suicidal thoughts.
3-20. The answer is c. (Martin, pp 42–49; Afifi, pp 148–153.) The combined deficit in which the patient loses ability to (use his lateral rectus muscle) abduct his right eye and display facial expression on the right side of
the face means that the lesion is located in the dorsal pons at the site where
the facial nerve curves around (just above) the motor nucleus of cranial
nerve VI. Thus, a lesion at this site will affect both cranial nerves, causing
the combined deficits described previously.
226
Clinical Vignettes for the USMLE Step 1
3-21. The answer is a. (Cotran, pp 177–179.) Fragile X syndrome is one
of four diseases that are characterized by long repeating sequences of three
nucleotides. The other diseases are Huntington’s disease, myotonic dystrophy, and spinal and bulbar muscular atrophy. The fragile X syndrome,
which is more common in males than females, is one of the most common
causes of familial mental retardation. Additional clinical features of this disorder include developmental delay, a long face with a large mandible, large
everted ears, and large testicles (macroorchidism). Examination of the DNA
from patients with fragile X syndrome reveals multiple tandem repeats of
the nucleotide sequence CGG on the X chromosome. Normally these
repeats average up to 50 in number, but in patients with fragile X syndrome
there are more than 230 repeats. This number of repeats is called a full
mutation. Normal transmitting males (NTMs) and carrier females have
between 50 and 230 CGG repeats. This number of repeats is called a premutation. During oogenesis, but not spermatogenesis, premutations can be
converted to mutations by amplification of the triplet repeats. This explains
the much higher incidence of mental retardation in grandsons rather than
brothers of normal transmitting males (Sherman’s paradox), as the premutation is amplified in females but not in males. Since the premutation is not
amplified in males, no daughters of NTMs are affected. An additional finding associated with these repeat units is anticipation, which refers to the
fact that the disease is worse in subsequent generations.
3-22. The answer is b. (Levinson, pp 302–303.) The figure presented in
the question shows a Cryptosporidium oocyst stained with a fluorescentlabeled specific antibody. Cryptosporidium may also be stained with a modified acid-fast stain but are not acid-fast bacilli. They are smaller than
Cyclospora, which are yeast size, but larger than Enterocytozoon, one of the
microsporidia.
3-23. The answer is a. (Hardman, pp 705–706.) Patients at increased
risk of developing hyperkalemia should not receive K-sparing diuretics.
Potassium-sparing diuretics appear to block Na channels in the luminal
membrane of the late distal tubules and the collecting duct. A mild excretion of Na occurs because of the relatively low capacity to reabsorb it in this
portion of the nephron. Loop diuretics and thiazides typically increase K
excretion.
Block 3
Answers
227
3-24. The answer is d. (Cotran, pp 562–563.) Cardiac rupture, whether
of free wall, septum, or papillary muscle, occurs in only 1 to 5% of cases
following acute myocardial infarction. It occurs usually within the first
week of infarction, when there is maximal necrosis and softening (4 to 5
days) and is very rare after the second week. Rupture of the free wall results
in pericardial hemorrhage and cardiac tamponade. Rupture of the interventricular septum causes a left-to-right shunt. Serious mitral valve incompetence results from rupture of anterior or posterior papillary muscles.
This valve incompetence can produce signs of mitral regurgitation, including a new pansystolic murmur along with a diastolic flow murmur. Indeed,
the onset of a new murmur following a myocardial infarction should raise
the possibility of papillary rupture.
Other common complications of myocardial infarction include
arrhythmias such as heart block, sinus arrhythmias, or ventricular tachycardia or fibrillation. These occur in 90% of complicated cases. Next in
importance, but not in frequency (only 10%), is cardiogenic shock from
severe left ventricular contractile incompetence. Milder left ventricular failure with lung edema occurs in 60% of these cases, while mural thrombosis
with peripheral emboli may occur in up to 40%. Ventricular aneurysm
forms a “bulge” of the left ventricular chamber; it consists of scar tissue and
does not rupture, but may contain a thrombus. Sudden cardiac death
occurs within 2 h in 20% of patients with acute myocardial infarction.
3-25. The answer is e. (Murray, pp 307–346. Scriver, pp 2007–2056. Sack,
pp 121–138. Wilson, pp 287–317.) In the synthesis of cysteine, the following
sequence of steps occurs, where SAM is S-adenosylmethionine, CS is cystathionine synthase, cys is cysteine, and α-KG is α-ketoglutarate:
methionine → SAM → homocysteine + adenosine
homocysteine + serine → cystathionine → cys + α-KG + NH4+
(CS, B6)
Cystathionine synthetase, a pyridoxal phosphate (vitamin B6) enzyme, catalyzes the condensation of serine and homocysteine to form cystathionine. A
deficiency of this enzyme leads to a buildup of homocysteine, which oxidizes
to form homocystine. This may result in mental retardation, but sometimes
causes dislocated lenses and a tall, asthenic build reminiscent of Marfan’s
228
Clinical Vignettes for the USMLE Step 1
syndrome. Patients with homocystinuria also have a clotting diathesis,
requiring care to avoid dehydration during anesthesia. Their cysteine deficiency must be made up from dietary sources. In some cases, dietary intake
of vitamin B6 (pyrixodal phosphate) may alleviate symptoms because of its
requirement by the crucial enzymes.
3-26. The answer is a. (Ash, pp 160–163.) The febrile paroxysms of Plasmodium malariae malaria occur at 72-h intervals; those of P. falciparum and
P. vivax malaria occur every 48 h. The paroxysms usually last 8 to 12 h with
P. vivax malaria but can last 16 to 36 h with P. falciparum disease. In P. vivax,
P. ovale, and P. malariae infections, all stages of development of the organisms can be seen in the peripheral blood; in malignant tertian (P. falciparum)
infections, only early ring stages and gametocytes are usually found.
3-27. The answer is c. (Murray, pp 48–62. Scriver, pp 3–45. Sack, pp 1–3.
Wilson, pp 101–120.) In the technique of polyacrylamide gel electrophoresis
(PAGE), the distance that a protein is moved by an electrical current is
proportional to its charge and inversely proportional to its size. Patients
with normal hemoglobin A have two α-globin and two β-globin chains,
each encoded by a pair of normal globin alleles. Mutation in one α- or
β-globin allele alters the primary amino acid sequence of the encoded globin peptide. If the amino acid change alters the charge of the peptide, then
the hemoglobin tetramer assembled with the mutant globin peptide has a
different charge and electrophoretic migration than the normal hemoglobin
tetramer. The electrophoresis of native (undenatured) hemoglobin therefore
produces two species (two bands) rather than one, each retaining its heme
molecule and red color. If the hemoglobins were first denatured into their
α-globin and β-globin chains as with SDS-polyacrylamide gel electrophoresis, then the similar size of the α- or β-globin peptides would cause them to
move closely together as two colorless bands. Identification of these peptides as globin would require use of labeled antibody specific for globin
(western blotting). Since the sodium dodecyl sulfate (SDS) detergent covers
the protein surface and causes all proteins to be negatively charged, the distance migrated is solely dependent (inversely proportional) to protein size.
High-performance liquid chromatography (HPLC) uses ionic resins to separate proteins by charge. The columns are run under high pressure, rapidly
producing a series of proteins that are separated from most negative to most
positive (or vice versa, depending on the charge of the ionic resin). A mutant
Block 3
Answers
229
hemoglobin with altered charge should produce a second red protein in the
pattern. In dialysis, semipermeable membranes allow smaller proteins to
diffuse into the outer fluid, but not larger proteins such as hemoglobin.
3-28. The answer is e. (Guyton, pp 742–744, 768–769.) Analysis of
serum electrolytes reveals low potassium (hypokalemia), low chloride
(hypochloremia), and metabolic alkalosis. These abnormalities arise from
two sources. First, gastric juice contains potassium and chloride in concentrations higher than found in the plasma. Loss of gastric juice through
vomiting or drainage leads to depletions of these electrolytes from the
plasma. Second, the metabolic abnormalities are exacerbated by the student’s dehydration. Contraction of the vascular volume leads to orthostatic
hypotension and the activation of renal mechanisms important for conserving volume. As a result, water, sodium, and bicarbonate are reabsorbed
at the expense of increased potassium and hydrogen excretion.
3-29. The answer is b. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp
97–158. Wilson, pp 23–39.) Albinism is one of many genetic diseases that
exhibit locus heterogeneity, which means that mutations at several different
loci can produce identical phenotypes. The two McKusick numbers provide a clue that there is more than one locus for albinism, both causing
autosomal recessive disease. Each parent must be homozygous for a
mutant allele from one albinism locus but heterozygous or homozygous
normal at the other locus. Their child would then be an obligate carrier for
each type of albinism. A new mutation in the child is also possible, converting one of the parental mutant alleles to normal, but this would be very
rare. Autosomal dominant disorders often vary in severity within families
(variable expressivity) but occasionally are clinically silent in a person
known to carry the abnormal allele (incomplete penetrance).
3-30. The answer is b. (Cotran, pp 1055–1056. Rubin, pp 991–992.) Dysfunctional uterine bleeding (DUB) is defined as abnormal uterine bleeding
that is due to a functional abnormality rather than an organic lesion of the
uterus. In contrast, secondary dysmenorrhea refers to painful menses
associated with an organic cause, such as endometriosis, which is the most
common cause. Most cases of DUB are related to an endocrine abnormality affecting the hypothalamic-pituitary-ovarian axis. The three main
categories of DUB are anovulatory cycles (the most common form), inad-
230
Clinical Vignettes for the USMLE Step 1
equate luteal phase, and irregular shedding. Anovulatory cycles consist of
persistence of the Graafian follicle without ovulation. This results in continued and excess estrogen production without the normal postovulatory
rise in progesterone levels. With no progesterone production, no secretory
endometrium is formed. Instead, biopsies reveal nonsecretory (proliferative) endometrium with mild hyperplasia. The mucosa becomes too thick
and is sloughed off, resulting in the abnormal bleeding. Anovulatory
cycles characteristically occur at menarche and menopause. They are also
associated with polycystic ovary (Stein-Leventhal) syndrome. It is important to note that other causes of unopposed estrogen effect can lead to this
appearance of a proliferative endometrium with mild hyperplasia. These
causes include exogenous estrogen administration or estrogen-secreting
neoplasms, such as a granulosa cell tumor of the ovary or an adrenal cortical neoplasm. If there is ovulation but the functioning of the corpus
luteum is inadequate, then the levels of progesterone are decreased, resulting in asynchrony between the chronologic dates and the histologic
appearance of the secretory endometrium. This is referred to as an inadequate luteal phase (luteal phase defect) and is an important cause of infertility. Biopsies are usually performed several days after the predicted time
of ovulation. If the histologic dating of the endometrium lags 4 or more
days behind the chronologic date predicted by the menstrual history, the
diagnosis of luteal phase defect can be made. Clinically, these patients
exhibit low serum progesterone, FSH, and LH levels. In contrast, prolonged functioning of the corpus luteum (persistent luteal phase with continued progesterone production) results in prolonged heavy bleeding at
the time of menses. Histologically, there is a combination of secretory
glands mixed with proliferative glands (irregular shedding). Clinically,
these patients have regular periods, but the menstrual bleeding is excessive and prolonged (lasting 10 to 14 days). Current oral contraceptives,
being a combination of estrogen and progesterone, cause the endometrium to include inactive glands with predecidualized stroma. The endometrium in postmenopausal women reveals an atrophic pattern with
atrophic or inactive glands.
3-31. The answer is e. (Sweeney, pp 14–15, 91, 108, 122, 154. Moore,
Developing Human, pp 189, 435.) Vitamin A is a member of the retinoic acid
family. Retinoic acid directs the polarity of development in the central nervous system, the axial skeleton (vertebral column), and probably the
Block 3
Answers
231
appendicular skeleton as well. Retinoic acid turns on various combinations
of homeobox genes, depending on tissue type and location (distance and
direction from the source of retinoic acid). Exogenous sources of retinoic
acid may induce the wrong sequence or combination of homeobox genes,
leading to structural abnormalities in the nervous and skeletal systems. The
other organ systems listed are not as susceptible to vitamin A.
3-32. The answer is d. (Katzung, p 940. Hardman, p 1267.) The potential
serious adverse effect of bleomycin is pneumonitis and pulmonary fibrosis.
This adverse effect appears to be both age- and dose-related. The clinical
onset is characterized by decreasing pulmonary function, fine rales, cough,
and diffuse basilar infiltrates. This complication develops in approximately
5% to 10% of patients treated with bleomycin. Thus, extreme caution must
be used in patients with a preexisting history of pulmonary disease. All of
the other drugs listed in the question are effective against carcinomas and
have not been associated with significant lung toxicity.
3-33. The answer is b. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp
97–158. Wilson, pp 361–391.) Succinylcholine is metabolized by a plasma
enzyme formerly called pseudocholinesterase [now called butyrylcholinesterase (BChE) to designate its favored substrate]. Approximately 1
in 100 individuals are homozygous for a variant of BChE that has 60% activity, while 1 in 150,000 individuals are homozygous for a variant with 33%
activity. The latter group exhibits prolonged recovery from succinylcholineinduced anesthesia, a phenotype known as succinylcholine apnea. As with
most enzyme defects, succinylcholine apnea exhibits autosomal recessive
inheritance. The father is presumably homozygous for a BChE variant, like
his two deceased siblings, but has not undergone anesthesia to display the
phenotype. His daughter is also likely to be homozygous, implying that her
mother is a heterozygote. (Note that the BChE variant with 60% activity has
a heterozygote frequency of 1/5 by application of the Hardy-Weinberg law.)
3-34. The answer is c. (Braunwald, p 985.) The rash is impetigo, which
is caused by group A streptococci, occasionally by other streptococci, and
also by Staphylococcus aureus. It occurs in children who have poor hygiene,
and the streptococci, which colonize the skin, gain entrance through a
break in the skin, such as a scratch or an insect bite. The rash is painless,
unlike herpes simplex or shingles, which is due to Herpesvirus varicellae.
232
Clinical Vignettes for the USMLE Step 1
Herpes simplex occurs on the face and mouth and genitals; shingles follows the distribution of a nerve, mainly the temporal nerve and the intracostal nerves. Scarlet fever, also due to streptococci, characteristically
covers the trunk and extremities with a fine papular rash, sparing the
palms and soles. Erysipelas is a streptococcal cellulitis.
3-35. The answer is d. (Howard, pp 755–756.) Hepatitis E virus (HEV) is
a single-stranded RNA virus. It is transmitted enterically, and the disease is
often referred to as enteric hepatitis C. There is no test for HEV routinely
available. Diagnosis is clinical and also one of exclusion.
3-36. The answer is e. (Taylor, pp 418–424.) Of the psychological
defense mechanisms listed, denial is the most common. Most defense
mechanisms involve an unconscious mental process and are protective
measures for the relief of anxiety or guilt. In denial, the patient attempts to
reject the threat of the perception of illness and the developing anxiety.
While failure to face one’s illness can be harmful, denial can also be a useful defense mechanism, especially during recovery or rehabilitation. In
rationalization, a patient attempts to justify an irrational feeling, behavior,
or thought. Projection involves attributing one’s own problem or conflict to
another person or situation. In displacement, a feeling, thought, wish, or
fear that is unacceptable is transferred to another person or situation. Sublimation is a defense mechanism whereby wishes that are unacceptable are
diverted into acceptable channels; thus partial gratification is achieved.
3-37. The answer is b. (Gilroy, p 337; Kandel, pp 951–953.) Sleep apnea
can occur for several reasons. One common basis is an obstruction of the
airways (called obstructive sleep apnea). In this case, as indicated in the
statement of the question, the physicians ruled out this possibility. Another
possible cause involves central sleep apnea. This is due to disruption of the
mechanism involving chemoreceptors in the carotid body that monitors
carbon dioxide and oxygen levels in the blood. Axons in the carotid body
project via the glossopharyngeal nerve (IX) to the reticular formation of the
medulla. Therefore, disturbances involving the carotid body could result in
central sleep apnea. Here, inappropriate signals are sent to the medullary
reticular formation, which, in part, projects caudally to ventral horn sites in
the spinal cord, governing such muscles as those that regulate the
diaphragm and, therefore, disrupt the normal breathing process.
Block 3
Answers
233
3-38. The answer is d. (Moore, Developing Human, pp 22–23.) In man the
time required for the progression from spermatogonium to motile spermatozoon is about two months (61 to 64 days). Spermatogenesis, the process
by which spermatogonia undergo mitotic division to produce primary
spermatocytes, occurs at 1°C (2°F) below normal body temperature. Subsequent meiotic divisions produce secondary spermatocytes with a bivalent haploid chromosome number and then spermatids with a monovalent
haploid chromosome number. The maturation of the spermatid, spermiogenesis, results in spermatozoa. Morphologically adult spermatozoa are
moved to the epididymis where they become fully motile.
3-39. The answer is d. (Hardman, pp 701–702, 704. Katzung, p 741.)
Hydrochlorothiazide is recommended in the treatment of idiopathic hypercalciuria because of its ability to decrease the excretion of Ca. The loop
diuretics are contraindicated because they increase urinary Ca excretion.
The mechanism for decreased Ca excretion by the thiazides is not known,
but it is thought that inhibition of NaCl co-transport in the distal tubules
by thiazides causes membrane depolarization. This results in the opening
of the Ca channels followed by the reabsorption of Ca.
3-40. The answer is b. (Kandel, p 544; Nolte, pp 422–424.) This large
pituitary tumor is seen to compress the optic chiasm. Damage to the chiasm affects the crossing fibers of the nasal retina, which convey information
from the temporal visual fields. This results in a bitemporal hemianopsia.
Since some parts of the optic nerves are spared, pupillary reflexes are preserved. The neuroanatomic substrates for conjugate gaze (i.e., frontal eye
fields; pontine gaze center; medial longitudinal fasciculus; and nuclei of
cranial nerves III, IV, and VI) are unaffected by the tumor; the mechanism
of conjugate gaze remains intact.
3-41. The answer is b. (Baum, pp 306–310.) Biofeedback is a process of
learning to control various components of one’s autonomic responses by
using visual or auditory feedback of information from one’s physiologic
functions. The feedback of information about one’s physiologic responses
and one’s ability to learn and practice control can be influenced by such factors as motivation, feelings, attitude, and interpersonal relations, but information feedback is the primary component in the learning process. Just as
one learns to improve one’s motor skills by feedback of information and
234
Clinical Vignettes for the USMLE Step 1
observations of distance, time, space, improvement, and so on, one can
learn to exert influence on physiologic responses. Formerly these physiologic responses had been regarded as autonomic because we had no visual
electronic or mechanical mechanism for feeding back such information.
3-42. The answer is c. (Cotran, pp 1029–1033.) Knowledge of the
anatomic division of the prostate is important in understanding the locations of the major pathologic diseases of the prostate. Most adenocarcinomas of the prostate originate in the peripheral zone, while hyperplastic
nodules originate in the transition zone. This anatomic differentiation is
the result of the physiologic fact that the transition zone is particularly
estrogen-sensitive, while the peripheral zone is particularly androgensensitive. Dihydrotestosterone (DHT), which is formed from testosterone
by the action of 5-α-reductase, is responsible for the development of the
prostate during fetal growth and also at the time of puberty. With aging,
DHT levels are increased in the prostate, where DHT binds to nuclear DNA
and causes prostatic hyperplasia. This hyperplastic effect by DHT is augmented by estrogen, which appears to function by induction of androgen
receptors, and therefore this hyperplasia occurs in the portion of the
prostate that is particularly estrogen-sensitive.
3-43. The answer is a. (Baum, pp 99, 173–174.) Bereavement from the
loss of a loved one has been found to reduce the responsiveness of lymphocytes to mitogens. The same reaction occurs as a result of certain lifestyle
factors, such as cigarette smoking and alcohol consumption. Psychological
and social stress not only suppresses the immune system, but also suppresses DNA synthesis and DNA repair. Lack of close personal or family ties
has been associated with reduced immune competence and with tumor
growth. Environmental, physiologic, and psychosocial factors are thought
to trigger the development and growth of cancer by suppressing the “surveillance” function of the immune system, which protects the body from
invasion of alien cells and viruses. Exercise improves normal bodily functions, so the usual defense mechanisms should help protect against rather
than enhance tumor growth.
3-44. The answer is e. (McPhee, pp 531–535. Braunwald, pp 2105–2107.)
Hypothyroid patients tend to gain weight. Prolactin-secreting tumors (prolactinomas), being located in the pituitary, would be expected to show
Block 3
Answers
235
abnormal physical examination findings at the eyes, given that the tumor
typically sits on the optic chiasma. Early menopause is unlikely in a 22year-old. Resistance to LH and FSH would have prohibited this patient
from ever having menses. This leaves excessive exercise as the only remaining plausible cause in this patient.
3-45. The answer is e. (Howard, p 860.) While the essential information
(i.e., the evidence that the child in question was scratched by a cat) is missing, the clinical presentation points to a number of diseases, including catscratch disease (CSD). Until recently, the etiologic agent of CSD was
unknown. Evidence indicated that it was a pleomorphic, rod-shaped bacterium that had been named Afipia. It was best demonstrated in the affected
lymph node by a silver impregnation stain. However, it now appears that
Afipia causes relatively few cases of CSD and that the free-living rickettsia
primarily responsible is Rochalimaea henselae, which has recently been
renamed Bartonella henselae.
3-46. The answer is b. (Moore & Dalley, pp 187, 191, 205–207.) The
ilioinguinal nerve innervates the portion of the internal oblique muscle
inserting in the lateral border of the conjoint tendon. Paralysis of these
fibers would create weakness in the conjoint tendon, allowing herniation
to occur medial to the inferior epigastric vessels. The genitofemoral nerve
supplies sensory innervation to the skin of the femoral triangle and scrotum/labia majora. The subcostal nerve (T12) supplies lower portions of the
external abdominal oblique muscle. The pelvic splanchnic nerves supply
autonomic (parasympathetic) innervation to the pelvic viscera. The tenth
thoracic spinal nerve (T10) supplies abdominal muscles superior to the
inguinal region.
3-47. The answer is a. (Hardman, p 221. Katzung, p 131.) Methylphenidate
is similar to amphetamine and acts as a CNS stimulant, with more pronounced effects on mental than on motor activities. It is effective in the treatment of narcolepsy and attention-deficit hyperactivity disorders.
3-48. The answer is a. (Moore, Developing Human, p 276.) Blockage
of the foregut in the newborn produces projectile vomiting. Congenital
hypertrophic pyloric stenosis, occurring in 0.5 to 1.0% of males and rarely
in females, involves hypertrophy of the circular layer of muscle at the
236
Clinical Vignettes for the USMLE Step 1
pylorus. This usually does not regress and must be treated surgically. During the fifth and sixth weeks of development, the lumen of the duodenum
is occluded by muscle proliferation but normally recanalizes during the
eighth week. Failure of recanalization results in duodenal atresia. Because
this occurs distal to the hepatopancreatic ampulla, the vomitus will occasionally be stained with bile. Annular pancreas, rare in itself, seldom completely blocks the duodenum. Imperforate anus results in intestinal
distention with bloating.
3-49. The answer is a. (Murray, pp 1217–1225.) While all fungi such as
Candida and Cryptococcus are potentially serious in a bone marrow transplant unit (BMTU), the most frequent cause of fungal infection and death
is Aspergillus. Aspergilli are ubiquitous in the environment. There are
instances of multiple infections in new units that have not been monitored
prior to opening or in units adjacent to construction projects. Strict precautions should be taken to exclude dust and debris from the BMTU area
during construction, but in any event the environment should be monitored for airborne microorganisms, especially Aspergillus, prior to opening
the unit.
3-50. The answer is c. (Braunwald, p 270.) Lithium therapy results in
nephrogenic diabetes insipidus. These patients maintain a high normal
serum osmolarity unless water intake is restricted because the thirst center
is intact and able to regulate serum osmolarity by water intake. They develop hypernatremia if they are hospitalized or develop CNS problems.
BLOCK 4
Answers
4-1. The answer is a. (Cotran, pp 516, 521–522. Rubin, pp 515–516.
Damjanov, pp 1429–1431.) Leukocytoclastic angiitis refers to the histologic
finding of fragmented neutrophils surrounding small blood vessels. The
differential diagnosis of leukocytoclastic vasculitis includes microscopic
polyarteritis nodosa and three other disorders: Henoch-Schönlein purpura, Wegener’s granulomatosis, and Churg-Strauss syndrome. HenochSchönlein purpura is a disorder of children who present with hemorrhagic
urticaria and hematuria following an upper respiratory infection. The
pathology of this disease involves the deposition of IgA immune complexes in small vessels of the skin. Because the antibody is IgA, the alternate complement pathway is activated in these patients. Wegener’s
granulomatosis (WG) is characterized by acute necrotizing granulomas of
the upper and lower respiratory tract, focal necrotizing vasculitis affecting
small to medium-sized vessels, and renal disease. Histologically there is
fibrinoid necrosis of small arteries, early infiltration by neutrophils, and
granuloma formation with giant cells. The peak incidence is in the fifth
decade, and many patients have C-ANCAs. The disease is highly fatal,
with death occurring within 1 year, unless recognized and treated with
immunosuppressive agents. Churg-Strauss syndrome (allergic vasculitis)
is a form of necrotizing vasculitis with granulomas of the respiratory tract
and asthma. The disorder is associated with increased serum IgE and
peripheral eosinophilia.
4-2. The answer is c. (McPhee, pp 530, 539. Braunwald, pp 812–817.)
Pelvic inflammatory disease is a cause of tubal scarring, setting the stage
for an ectopic (tubal) pregnancy. As the pregnancy grows, the tube is
stretched, causing pain. Endometriosis causes pain with each menstrual
cycle, which is not the case here. Urinary tract infection can cause pain,
but she would be expected to have dysuria. Placental abruption occurs
only after 20 weeks of pregnancy. She is clearly not premenstrual, because
she is pregnant.
237
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
238
Clinical Vignettes for the USMLE Step 1
4-3. The answer is e. (Berne, 3/e, pp 258–260.) When a person rises suddenly, blood pools in the dependent portions of the body, causing decreases
in venous return, left ventricular end-diastolic volume, stroke volume, and
pulse pressure. The reduced stroke volume leads to a drop in cardiac output and, therefore, a drop in blood pressure. Decreased blood pressure
produces the baroreceptor reflex, leading to an increase in sympathetic
activity, which increases total peripheral resistance, cardiac contractility,
heart rate, and ejection fraction. These changes in the cardiovascular system return blood pressure toward normal.
4-4. The answer is c. (Moore & Dalley, pp 731, 742, 761.) All of the muscles listed are innervated by the posterior interosseus branch of the radial
nerve (the terminal part of the deep radial nerve). Extensor carpi radialis
longus, however, is innervated by a muscular branch of the radial nerve
proximal to the origin of the deep branch. Its function would, therefore, be
preserved in entrapment of the posterior interosseus nerve.
4-5. The answer is e. (Moore & Dalley, pp 731, 742, 761.) Each of the
muscles listed is innervated by the deep branch of the radial nerve or its
terminal portion, the posterior interosseus nerve. The deep radial nerve
passes between the deep and superficial layers of the supinator muscle and
lies on a bare area of the radius where it may be compressed by action of
the supinator or damaged by a fracture of the radius.
4-6. The answer is d. (Hardman, p 564. Katzung, pp 370, 1013.) Flumazenil is a competitive antagonist of benzodiazepines at the GABA receptor.
Repeated administration is necessary because of its short half-life relative to
that of most benzodiazepines.
4-7. The answer is c. (Cotran, pp 670–675.) The diagnosis of Hodgkin’s
disease depends on the clinical findings added to the total histologic picture,
which includes the presence of binucleated or bilobed giant cells with prominent acidophilic “owl-eye” nucleoli known as Reed-Sternberg (RS) cells.
However, cells similar in appearance to RS cells may also be seen in infectious
mononucleosis, mycosis fungoides, and other conditions. Thus, while RS
cells are necessary for histologic confirmation of the diagnosis of Hodgkin’s
disease, they must be present in the appropriate histologic setting of lymphocyte predominance, nodular sclerosis, mixed cellularity, or lymphocyte
Block 4
Answers
239
depletion to make the correct diagnosis. In contrast, Call-Exner bodies are
seen in granulosa cell tumors of the ovary, Hürthle cells are associated with
Hashimoto’s thyroiditis, Sézary cells are associated with mycosis fungoides,
and strap cells are seen in skeletal muscle tumors, such as rhabdomyomas.
4-8. The answer is c. (Hardman, p 1302.) Muromonab-CD3 is a monoclonal antibody that interferes with T cell function. It is classified as an
immunosuppressive drug. This drug is given intravenously and is indicated in the treatment of acute allograft rejection. Generally, azathioprine
and prednisone are used along with muromonab-CD3. Interferon α and
aldesleukin (interleukin 2) are cytokines that are classified as immunostimulants. Sargramostim and filgrastim are also immunostimulants. These
drugs are produced by recombinant DNA technology. Sargramostim is a
human granulocyte-macrophage colony stimulating factor (GM-CSF), and
filgrastim is a human granulocyte colony stimulating factor (G-CSF).
4-9. The answer is e. (Afifi, pp 209–213.) The cranial nerve involved in
adduction of the eye is cranial nerve III, in which the act of moving the eye
medially is governed by the medial rectus muscle. Cranial nerve III is
located near the midline of the rostral half of the midbrain just below the
midbrain periaqueductal gray.
4-10. The answer is e. (Baum, pp 363–372.) Evaluations of treatment
methods using the classical conditioning model have demonstrated that
relapse is more likely to occur in the presence of alcohol-associated stimuli.
Thus, the most effective treatment conditions should maintain an environment that is as free as possible of alcohol-associated stimuli, and the patient
should be returned to an environment that is different from the one in
which dependence was acquired. Since dependence is acquired by the
patient’s developing alcohol-compensatory conditioned responses, specific, therapeutic strategies should be implemented and practiced over time
prior to discharge to extinguish these alcohol-compensatory conditioned
responses. Aversive affective states, such as depression or anxiety, can also
act to increase the likelihood of relapse, so all treatment procedures should
attempt to extinguish conditioned associations between aversive affective
states and alcohol. The patient will probably experience relief from withdrawal symptoms if allowed to substitute other drugs; thus the very conditioned responses targeted for extinction will be maintained.
240
Clinical Vignettes for the USMLE Step 1
4-11. The answer is b. (Moore & Dalley, p 299.) Tuberculous infections
of the lumbar vertebrae are frequently communicated to the sheath of the
adjacent psoas muscles. Subsequently, pus may travel inferiorly over the
pelvic brim and erupt on the anterior thigh near the insertion of the psoas
on the lesser trochanter of the femur. Abscesses in the ischiorectal fossae
may drain into the pelvis or the anal canal. The inguinal ligament passes
laterally to medially superficial to the psoas muscle to transmit contents
to the scrotum or labia. Its origin in the anterolateral abdominal wall is
not in close approximation to the lumbar vertebrae. The paracolic gutters
can spread infection or metastases into the pelvis or the subphrenic
region, depending on whether the patient is erect or supine.
4-12. The answer is e. (Katzung, pp 141, 168.) Prazosin blocks
α1-adrenergic receptors in arterioles, thereby decreasing peripheral resistance and leading to a decrease in blood pressure. Orthostatic hypotension can occur, particularly after a first dose.
4-13. The answer is d. (Braunwald, p 1549.) Urine dipstick cannot
detect light chains and Bence Jones proteins found in paraproteinemias. So
there is a discrepancy between dipstick values and the 24-h urine collection. The sulfosalicylic acid test (SSA) can precipitate all proteins and can
be diagnostic as well. Focal sclerosis and amyloidosis would not have this
discrepancy. Hypertensive nephrosclerosis presents with milder degrees of
proteinuria.
4-14. The answer is d. (Guyton, pp 428–429.) Hemostasis following
blood vessel injury depends on (1) vascular spasm, (2) formation of a
platelet plug, and (3) clot formation. When injury to a vessel produces only
a small defect, the platelet plug itself can cause hemostasis. This is the basis
for the bleeding time that is employed clinically to distinguish hemostatic
abnormalities caused by platelet abnormalities from those caused by coagulation defects. Aspirin diminishes platelet aggregation by inhibiting
cyclooxygenase, an enzyme required for generation of thromboxanes,
which promote platelet aggregation. All the other situations described in
the question are associated with coagulation deficiency. Persons thus
affected would have a normal bleeding time but would present clinically
with delayed posttraumatic bleeding caused by their inability to form an
effective clot to reinforce the platelet plug.
Block 4
Answers
241
4-15. The answer is b. (Murray, pp 230–267. Scriver, pp 2297–2326. Sack,
pp 121–138. Wilson, pp 287–320.) Untreated ethylene glycol of antifreeze can
be converted to the kidney toxin oxalate crystals. This occurs by oxidation
of ethylene glycol. The first committed step in this process is the oxidation
of ethylene glycol to an aldehyde by alcohol dehydrogenase. This is normally the route for converting ethanol (drinking alcohol) to acetate. Patients
who have ingested ethylene glycol or wood alcohol (methanol) are placed
on a nearly intoxicating dose of ethanol by a nasogastric tube together with
intravenous saline and sodium bicarbonate. This treatment is carried out
intermittently along with hemodialysis until no traces of ethylene glycol are
seen in the blood. Ethanol acts as a competitive inhibitor of alcohol dehydrogenase with respect to ethylene glycol or methanol metabolism.
4-16. The answer is b. (Howard, pp 819–821.) The highest risk of fetal
infection with rubella occurs during the first trimester. In seronegative
patients, the risk of infection exceeds 90%. However, before other measures (such as termination of pregnancy) are considered, a rubella immune
status must be performed. A rubella titer of 1:10 is protective.
4-17. The answer is d. (Cotran, pp 683–685.) Myeloid metaplasia with
myelofibrosis is a myeloproliferative disorder in which the bone marrow is
hypocellular and fibrotic and extramedullary hematopoiesis occurs, mainly
in the spleen (myeloid metaplasia). Marked splenomegaly with trilineage
proliferation of normoblasts, immature myeloid cells, and large megakaryocytes occur. Giant platelets and poikilocytic (teardrop) red cells are seen
in the peripheral smear. Clinically, myeloid metaplasia may be preceded by
polycythemia vera or chronic myeloid leukemia. Biopsy of the marrow is
essential for diagnosis. In contradistinction to chronic myeloid leukemia,
levels of leukocyte alkaline phosphatase are elevated or normal in myeloid
metaplasia; in CML, levels are low or absent. In 5 to 10% of cases of
myeloid metaplasia, acute leukemia occurs. In aplastic anemia the marrow
is very hypocellular, but consists largely of fat cells, not fibrosis. There is no
splenomegaly. Microangiopathic and other hemolytic anemias that result
from trauma to red cells show many erythrocytic abnormalities (helmet
and burr cells, triangle cells, and schistocytes) in the peripheral smear.
4-18. The answer is d. (Hardman, p 1346.) Heparin is a mixture of sulfated mucopolysaccharides and is highly acidic and highly charged. Pro-
242
Clinical Vignettes for the USMLE Step 1
tamine is a very basic polypeptide that combines with heparin. The complex
has no anticoagulant activity. Excess protamine does have anticoagulant
activity, so just enough should be given to counteract the heparin effect.
4-19. The answer is a. (Murray, pp 230–267. Scriver, pp 3827–3876. Sack,
pp 121–138. Wilson, pp 287–320.) Gangliosides are continually synthesized
and broken down. The specific hydrolases that degrade gangliosides by
sequentially removing terminal sugars are found in lysosomes. In the lipid
storage disease known as Tay-Sachs disease (272800), ganglioside GM2
accumulates because of a deficiency of β-N-acetylhexosaminidase, a lysosomal enzyme that removes the terminal N-acetylgalactosamine residue.
Homozygotes produce virtually no functional enzyme and suffer weakness,
retardation, and blindness. Death usually occurs before infants are 3 years
old. Carriers (heterozygotes) of the autosomal recessive disease produce
approximately 50% of the normal levels of enzyme but show no ill effects.
In high-risk populations, such as Ashkenazi Jews, screening for carrier status may be performed.
4-20. The answer is d. (Braunwald, p 1547.) All of these diseases are
common in older persons. Amyloidosis and light chain deposition disease
are related to paraprotein deposition in the kidney and typically present
with nephrotic syndrome. The subacute presentation and erythrocyte casts
in the urine along with the rapid decline in renal function are most consistent with vasculitis. A positive antineutrophil cytoplasmic antibody
(ANCA) would be supportive. Erythrocyte casts are not seen in the other
diseases.
4-21. The answer is d. (Hardman, pp 1676–1678. Katzung, pp 990–991.)
Carbon monoxide is a common cause of accidental and suicidal poisoning.
Its affinity for hemoglobin is 250 times greater than that of O2. It therefore
binds to hemoglobin and reduces the O2-carrying capacity of blood. The
symptoms of poisoning are due to tissue hypoxia; they progress from
headache and fatigue to confusion, syncope, tachycardia, coma, convulsions, shock, respiratory depression, and cardiovascular collapse. Carboxyhemoglobin levels below 15% rarely produce symptoms; above 40%,
symptoms become severe. Treatment includes establishment of an airway,
supportive therapy, and administration of 100% O2. Sulfur dioxide, ozone,
and nitrogen dioxide are mucous membrane and respiratory irritants.
Methane is a simple asphyxiant.
Block 4
Answers
243
4-22. The answer is a. (April, pp 359–360.) Visceral afferent pain fibers
from the gallbladder travel through the celiac plexus, thence along the
greater splanchnic nerves to levels T5–T9 of the spinal cord. Thus, pain
originating from the gallbladder will be referred to (appear as if coming
from) the dermatomes served by T5–T9, which include a band from the
infrascapular region to the epigastrium.
4-23. The answer is a. (Moore & Dalley, pp 182–186.) The rectus sheath
is formed by the aponeuroses of the abdominal wall musculature. Between
the costal margin and the umbilicus, the aponeurosis of the internal
oblique muscle splits; one portion passes anterior and the other posterior
to the rectus abdominis muscle. The aponeurosis of the external oblique
muscle fuses with the anterior leaflet of the aponeurosis of the internal
oblique muscle to form the anterior wall of the rectus sheath. The aponeurosis of the transversus abdominis muscle fuses with the posterior leaflet of
the aponeurosis of the internal oblique muscle to form the posterior wall of
the rectus sheath. Approximately midway between the umbilicus and symphysis pubis, the aponeuroses of the internal oblique and transversus
abdominis muscles pass anterior to the rectus abdominis muscle to contribute to the anterior leaf of the rectus sheath. This abrupt transition
results in a free edge to the posterior rectus sheath, known as the arcuate
line (of Douglas). Between this line and the pubis, only the transversalis
fascia separates the rectus abdominis muscle from the peritoneum. It is
here, where the inferior epigastric artery gains access to the rectus sheath,
that ventral lateral (spigelian) herniation may occur.
4-24. The answer is b. (Hardman, p 1299. Katzung, p 609.) Nephrotoxicity
may occur in almost three-quarters of patients treated with cyclosporine. Regular monitoring of blood levels can reduce the incidence of adverse effects.
4-25. The answer is a. (Cotran, pp 1025–1027.) Inflammation of the
prostate (prostatitis) is characterized by finding at least 15 leukocytes per
high-power field in prostatic secretions. Prostatitis is classified as being
either acute or chronic. Patients with acute prostatitis present with the sudden onset of fever, chills, and dysuria. Acute prostatitis is usually caused by
bacteria that cause urinary tract infections, such as Escherichia coli. Chronic
prostatitis presents clinically as low back pain, dysuria, and suprapubic
discomfort. It is divided into chronic bacterial prostatitis, which is associated with recurrent urinary tract infections (UTIs) with the same organism,
244
Clinical Vignettes for the USMLE Step 1
and chronic abacterial prostatitis, which is not associated with recurrent
UTIs. Instead, chronic abacterial prostatitis is associated with infections
with either Chlamydia trachomatis or Ureaplasma urealyticum. Granulomatous prostatitis causes vague symptoms and has an unknown etiology. This
diagnosis is made histologically.
4-26. The answer is a. (Cotran, pp 516–518. Rubin, pp 516–517.) Giant
cell arteritis (temporal arteritis), although not a major public health problem, is an important disease to consider in the differential diagnosis of
patients of middle to advanced age who present with a constellation of
symptoms that may include migratory muscular and back pains (polymyalgia rheumatica), dizziness, visual disturbances, headaches, weight loss,
anorexia, and tenderness over one or both of the temporal arteries. The
cause of the arteritis (which may include giant cells, neutrophils, and
chronic inflammatory cells) is unknown, but the dramatic response to corticosteroids suggests an immunogenic origin. The disease may involve any
artery within the body, but involvement of the ophthalmic artery or arteries
may lead to blindness unless steroid therapy is begun. Therefore, if temporal arteritis is suspected, the workup to document it should be expedited
and should include a biopsy of the temporal artery. Frequently, the erythrocyte sedimentation rate (ESR) is markedly elevated to values of 90 or greater.
Whereas tenderness, nodularity, or skin reddening over the course of one of
the scalp arteries, particularly the temporal, may show the ideal portion for
a biopsy, it is important to recognize that the temporal artery may be segmentally involved or not involved at all even when the disease is present.
4-27. The answer is c. (Levinson, pp 147–148.) At the present time,
Lyme disease may be diagnosed clinically and serologically. Patients who
are from endemic areas such as eastern Pennsylvania and report joint pain
and swelling months subsequent to exposure to ticks must be evaluated
for Lyme disease and treated if the test is positive. Patients may also report
a variety of neurologic problems such as tingling of the extremities, Bell’s
palsy, and headache. IgM antibody appears soon after the tick bite (10
days to 3 weeks) and persists for 2 months; IgG appears later in the disease but remains elevated for 1 to 2 years, especially in untreated patients.
A significant IgG titer is at least 1:320. Most investigators feel that IgM
titers of 1:100 are significant; some investigators say that any IgM titer is
significant.
Block 4
Answers
245
4-28. The answer is d. (Moore & Dalley, pp 100–103, 162–163.) The lobe
indicated by the * is the left upper (or superior) lobe. The general orientation when viewing CTs is that the observer is looking up from the patient’s
feet. Therefore, the patient’s left is on your right. In addition, on the left, the
inferior (lower) lobe begins relatively high in the thoracic cavity and is posterior to the upper lobe.
4-29. The answer is a. (Hardman, p 1180. Katzung, pp 817–819.) Fluconazole indirectly inhibits ergosterol synthesis. It inhibits cytochrome
P450, which is a key enzyme system for cytochrome P450–dependent sterol
14-α-demethylase. This leads to accumulation of 14-α-sterols, resulting in
impairment of the cytoplasmic membrane.
4-30. The answer is b. (Baum, pp 157–159.) Fifteen percent of the population (more than 35 million people) in the United States have hypertension. Risk factors for hypertension constitute complex interactions between
behavioral, physiologic, and genetic factors. Age, race, and family history
have been the standard risk factors, but they are not modifiable. More
recently behavioral and environmental factors have been documented to
play a significant role in the pathogenesis of hypertension. Of these behavioral risk factors, eating behaviors related to high intake of dietary salt and
obesity are most relevant, followed by stress and personality factors, which
are again related to a person’s coping mechanisms. The complex interaction
of these behavioral factors over time is most significant. Compliance with
medical treatment is crucial after hypertension has developed, but not in its
pathogenesis.
4-31. The answer is d. (Levinson, pp 287–288.) Eumycotic mycetoma is
a slowly progressing disease of the subcutaneous tissues that is caused by a
variety of fungi. The term Madura foot has been used to describe the foot
lesion. Although several fungi have been isolated in the United States from
persons who have mycetoma, Pseudallescheria boydii appears to be one of
the most common. Other foot infections that may resemble Madura foot
are actinomycotic (bacterial) in nature. These are caused by Nocardia
brasiliensis and Actinomadura.
4-32. The answer is e. (Braunwald, p 246.) Hematemesis or vomiting of
blood represents an upper gastrointestinal (GI) source of blood loss. Bleed-
246
Clinical Vignettes for the USMLE Step 1
ing from the colon will be manifested by either by no change in the color
of the stools or by black, tarry-like stools (melena). Bleeding from the lungs
results in blood in the sputum (hemoptysis) and from the kidneys as blood
in the urine (hematuria), mainly microscopic hematuria.
4-33. The answer is e. (Murray, pp 298–307. Scriver, pp 1471–1488. Sack,
pp 217–218. Wilson, pp 361–384.) In the presence of insulin deficiency, a
shift to fatty acid oxidation produces the ketones such as acetoacetate that
cause metabolic acidosis. The pH and bicarbonate are low, and there is
frequently some respiratory compensation (hyperventilation with deep
breaths) to lower the PCO2, as in choice e. A low pH with high PCO2 would
represent respiratory acidosis (choices a and b—the low-normal bicarbonate values in these choices indicate partial compensation). Choice d represents respiratory alkalosis as would occur with anxious hyperventilation
(high pH and low PCO2, partial compensation with high bicarbonate).
Choice c illustrates normal values.
4-34. The answer is b. (Cotran, pp 1222–1224. Chandrasoma, pp
963–966.) Osteopenia (reduction in the amount of bone) is seen in osteoporosis, osteomalacia, and osteitis fibrosa. Osteoporosis is characterized by
qualitatively normal bone that is decreased in amount. Histologic bone sections reveal thin trabeculae that have normal calcification and normal
osteoblasts and osteoclasts. Osteoporosis predisposes patients to fractures
of weight-bearing bones, such as the femurs and vertebral bodies. Patients
typically have normal serum levels of calcium, phosphorus, alkaline phosphatase, and parathyroid hormone. Osteoporosis is classified as being primary or secondary. Primary osteoporosis, the most common type of
osteoporosis, occurs most often in postmenopausal women and has been
related to decreased estrogen levels. Cigarette smoking is also associated
with an increased incidence of osteoporosis. Clinically significant osteoporosis is related to the maximum amount of bone a person has (peak bone
mass), which is largely genetically determined. Secondary osteoporosis
develops secondary to many conditions such as corticosteroid administration, hyperthyroidism, and hypogonadism.
In contrast, osteopetrosis is a rare inherited disease characterized by
abnormal osteoclasts showing decreased functioning. This abnormality
results in reduced bone resorption and abnormally thickened bone. In
these patients, multiple fractures are frequent as the bones are structurally
Block 4
Answers
247
weak and abnormally brittle. Increased fragility of bones is also present in
osteomalacia (caused by abnormal vitamin D metabolism in adults) and
osteitis deformans (Paget’s disease). Osteitis fibrosa cystica (von Recklinghausen’s disease of bone) is seen with severe hyperparathyroidism and is
characterized by increased bone cell activity, peritrabecular fibrosis, and
cystic bone lesions.
4-35. The answer is f. (Katzung, p 972.) Azathioprine is a derivative that
is closely related to 6-MP, which is used as a cancer chemotherapeutic
agent, while azathioprine is used as an immunosuppressive agent because
it is more effective than 6-MP in this regard. Azathioprine is used in organ
transplantation, particularly kidney allografts. Like 6-MP, azathioprine is
biotransformed to an inactive product by xanthine oxidase. Allopurinol,
which inhibits this enzyme, can increase the therapeutic action of azathioprine and possibly its adverse reactions. The dosage of azathioprine should
be decreased in the presence of allopurinol.
4-36. The answer is c. (Howard, pp 680–681.) Consumption of raw fish
causes endemic diphyllobothriasis in Scandinavia and the Baltic countries.
While most people do not become ill, a small percentage (2%) develop
vitamin B12 deficiency anemia. The adult fish tapeworm has an affinity for
vitamin B12 and may induce a serious megaloblastic anemia. Parvovirus B 19
causes acute hemolytic anemia primarily in immunosuppressed patients.
Yersinia infection is common in Scandinavia but is not fish-borne and does
not cause anemia. The larval stage of T. solium is called cysticercus. Humans
usually acquire cysticercosis by ingestion of food and water contaminated
by infected human feces.
4-37 through 4-38. The answers are 4-37 b, 4-38 c. (Kandel, pp
480–484; Siegel, pp 1096–1098.) Research conducted over the past 2
decades has shown that the actions of morphine are mediated through opioid µ receptors, while other opioid receptors appear not to play a significant role. Likewise, dopamine receptors are not involved in this process.
The region of the brain where concentrations of opioid receptors are very
heavily concentrated is the midbrain periaqueductal gray. This region plays
an important role in the modulation of pain and is particularly responsive
to opioid activation by morphine. While other areas of the brain indicated
in question 4-37 may also contain opioid receptors, concentrations of this
248
Clinical Vignettes for the USMLE Step 1
receptor are not known to be high (including a structure such as the mammillary bodies for which no known functions have been identified). Moreover, none of these regions are known to play any role in the regulation of
pain.
4-39. The answer is a. (Murray, pp 15–26.) The equilibrium between an
acid and its conjugate base is defined by the Henderson-Hasselbalch equation:
[base]
[acid]
pH = pK a + log ᎏᎏ
or
[HCO3−]
[CO2]
pH = 6.1 + log ᎏᎏ
in the case of carbonic acid. Note that CO2 is the effective acid and HCO3−
the conjugate base for carbonic acid due to its complete dissociation in
water.
Given a pH of 7.1 in the cyanotic newborn, then 7.1 − 6.1 = 1 =
log (10) = log [HCO3−]/[CO2] = log [HCO3−]/0.03 × PCO2. Since the [HCO3−
] is 12 mM, the PCO2 × 0.03 must be 1.2 mM and the PCO2 40 mmHg. This
normal calculated value for PCO2 means that the baby must have metabolic
acidosis, a common accompaniment of hypoxia (low PO2) that can be
treated by providing oxygen or administering alkali to ameliorate the acidosis. If the baby had respiratory acidosis, the PCO2 would be elevated; this
would be treated by increasing the respiratory rate to blow off CO2. Renal
treatment of acidosis would require increasing acid excretion or alkali
retention. The lungs compensate acidosis with increased breathing rates or
tidal volumes to blow off CO2 and increase pH, the kidneys by retaining
HCO3−. The lungs can compensate alkalosis somewhat by decreasing
breathing rates or volumes to retain CO2 (and decrease oxygenation within
limits), the kidneys by increasing excretion of HCO3−.
4-40. The answer is c. (Levinson, pp 302, 306, 307, 320–335.) All the diseases listed in the question have significant epidemiologic and clinical features. Toxoplasmosis, for example, is generally a mild, self-limiting disease;
however, severe fetal disease is possible if pregnant women ingest Toxoplasma oocysts. Consumption of uncooked meat may result in either an
acute toxoplasmosis or a chronic toxoplasmosis that is associated with serious eye disease. Most adults have antibody titers to Toxoplasma and thus
would have a positive Sabin-Feldman dye test.
Trichinosis most often is caused by ingestion of contaminated pork
Block 4
Answers
249
products. However, eating undercooked bear, walrus, raccoon, or possum
meat also may cause this disease. Symptoms of trichinosis include muscle
soreness and swollen eyes.
Although giardiasis has been classically associated with travel in Russia, especially St. Petersburg (Leningrad), many cases of giardiasis caused
by contaminated water have been reported in the United States as well.
Diagnosis is made by detecting cysts in the stool. In some cases, diagnosis
may be very difficult because of the relatively small number of cysts
present. Alternatively, an enzyme immunoassay may be used to detect
Giardia antigen in fecal samples.
Schistosomiasis is a worldwide public health problem. Control of this
disease entails the elimination of the intermediate host snail and removal of
streamside vegetation. Abdominal pain is a symptom of schistosomiasis.
Visceral larva migrans is an occupational disease of people who are in
close contact with dogs and cats. The disease is caused by the nematodes
Toxocara canis (dogs) and T. cati (cats) and has been recognized in young
children who have close contact with pets or who eat dirt. Symptoms
include skin rash, eosinophilia, and hepatosplenomegaly.
4-41. The answer is a. (McPhee, p 145. Braunwald, pp 175–179.) Sounds
must be conducted through the middle ear and sensed by the cochlea and
CN VIII; then they are processed by the cochlear nuclei and CNS pathways. Conductive deafness is hearing loss due to external auditory canal
or middle ear disease. Sensineural deafness is a perceptive loss of hearing
due to disease of the inner ear or eighth nerve. In conductive deafness,
bone conduction is better than air conduction, and the reverse is the case
for sensineural deafness. Central deafness is caused by disease affecting
the central auditory pathways. Tinnitus an annoying noise in the ear that
is usually benign, often is caused by cochlear or eighth nerve disorders.
Hearing may be diminished, but the patient is not rendered fully deaf.
Presbyacusis is hearing loss due to advanced age.
4-42. The answer is e. (Katzung, p 184. Hardman, p 764.) Nitric oxide
is thought to be enzymatically released from nitroglycerin. It can then
react with and activate guanylyl cyclase to increase GMP, a vasodilator
due to its effect on increasing calcium efflux. It also indirectly causes the
dephosphorylation of the light chains of myosin. These actions lead to
the vasodilator effect of nitroglycerin. Reaction of nitric oxide occurs with
250
Clinical Vignettes for the USMLE Step 1
protein sulfhydryl groups. Tolerance may develop in part from a decrease
in available sulfhydryl groups. Autonomic receptors are not involved in
the primary response of nitroglycerin, but compensatory mechanisms
may counter the primary actions.
4-43. The answer is a. (Cotran, pp 15–18.) The cause of cell injury and
death may sometimes be inferred from the type of necrosis present. Coagulative necrosis, characterized by loss of the cell nucleus, acidophilic change
of the cytoplasm, and preservation of the outline of the cell, is seen in sudden, severe ischemia of many organs. It is not present, however, in acute
ischemic necrosis of the brain. Myocardial infarction resulting from the sudden occlusion of the coronary artery is a classic example of coagulative
necrosis. In contrast, with liquefactive necrosis the dead cells are completely
dissolved by hydrolytic enzymes. This type of necrosis can be seen in
ischemic necrosis of the brain, but classically it is associated with acute
bacterial infections. Fat necrosis, seen with acute pancreatic necrosis, is fat
cell death caused by lipases. Fibrinoid necrosis is an abnormality seen
sometimes in injured blood vessels where plasma proteins abnormally
accumulate within the vessel walls. Caseous necrosis is a combination of
coagulative and liquefactive necrosis, but the necrotic cells are not totally
dissolved and remain as amorphic, coarsely granular, eosinophilic debris.
This type of necrosis grossly has the appearance of clumped cheese. It is
classically seen in tuberculous infections. Gangrenous necrosis of extremities is also a combination of coagulative and liquefactive necrosis. In dry
gangrene the coagulative pattern is predominate, while in wet gangrene the
liquefactive pattern is predominate.
4-44. The answer is c. (Nolte, pp 418–423, 515–529.) The arterial occlusion involves both the temporal and occipital regions of cortex. Therefore,
it would affect Wernicke’s area as well as primary visual areas of the occipital lobe. The patient would most likely present with receptive aphasia as
well as a right homonymous hemianopsia. The lesion would not likely produce marked intellectual deficits since the prefrontal cortex was spared;
nor would it produce hemiballism since there was no damage to the subthalamic nucleus.
4-45. The answer is b. (Kandel, pp 1305–1309. Nolte, pp 120–128.)
Although the tissue affected involves parietal, temporal, and occipital
Block 4
Answers
251
lobes, the primary artery affected is the middle cerebral artery. The unusual
feature of this occlusion is that it appears that the middle cerebral artery
extends more caudally than usual. Nevertheless, the middle cerebral artery
is the only one of the choices presented that could account for the damage
to the temporal and parietal cortices. The anterior cerebral artery supplies
the medial aspects of the frontal and parietal lobes; the posterior cerebral
artery supplies the occipital cortex (visual areas); the posterior choroidal
artery mainly supplies part of the tectum, the medial and superior aspects
of the thalamus, and the choroid plexus of the third ventricle. The superior
cerebellar artery supplies the dorsolateral aspect of a portion of the pons
and the cerebellum.
4-46. The answer is e. (Braunwald, pp 459–461.) Empirical studies have
revealed a number of changes in eating habits that will significantly discourage the tendency to eat more food than is required by the body. Nutritional experts recommend that we eat more slowly, serve ourselves smaller
portions, wait at least 20 min after we have eaten our first serving before
taking a second one, restrict all our eating to one or two places in the
home, do not watch television or read while we are eating, and let family
and friends know that we are trying to cut down on food intake. In addition, we should go grocery shopping only after we have eaten a satisfying
meal, not leave food out where we repeatedly see it and can easily reach it
many times a day, try to spend less time in the kitchen, get someone else
in the family to clear the plates and put away the leftovers, and monitor
eating habits by keeping a detailed log or diary of all food intake. Such
activities will help to disrupt previously learned, but inappropriate, eating
behaviors and establish appropriate environmental conditions and eating
behaviors.
4-47. The answer is c. (Braunwald, pp 568, 1607.) The incidence of malignancy in duodenal ulcer is low, so a biopsy of the ulcer is not indicated.
Surgery or other procedures are not necessary in uncomplicated ulcers.
4-48. The answer is c. (McPhee, pp 544–548. Braunwald, pp 2088,
2091–2092.) Androgen insensitivity can present as an inability for a male
child to go into puberty. Low FSH and LH are expected to yield low testosterone levels. High FSH and LH are usually markers of end organ damage
and lack of feedback of testosterone on the pituitary due to low levels.
252
Clinical Vignettes for the USMLE Step 1
Puberty can be delayed by hypothyroidism, with FSH and LH usually
appropriate to the testosterone level. XXY karyotype (Klinefelter’s) often
has no effect on testosterone level.
4-49. The answer is a. (Cotran, pp 712–716.) Chronic obstructive pulmonary diseases (COPDs) are characterized by obstruction to airflow somewhere along the airways. These diseases may affect the bronchus, the
bronchiole, or the acinus. Asthma, bronchiectasis, and chronic bronchitis
affect primarily the bronchus, while emphysema affects primarily the acinus. Asthma is a pulmonary disease that is caused by excessive bronchoconstriction secondary to airways that are hyperreactive to numerous
stimuli. Asthma has been divided into extrinsic and intrinsic categories. The
extrinsic category includes atopic (allergic) asthma, occupational asthma,
and allergic bronchopulmonary aspergillosis. The intrinsic category includes nonreaginic asthma and pharmacologic asthma. The former is
related to respiratory tract infections, while the latter is often related to
aspirin sensitivity. These aspirin-sensitive patients often have recurrent
rhinitis and nasal polyps. In these patients the aspirin initiates an asthmatic
attack by inhibiting the cyclooxygenase pathway of arachidonic acid metabolism without affecting the lipoxygenase pathway. This causes the relative
excess production of the leukotrienes, which are bronchoconstrictors.
4-50. The answer is i. (Katzung, p 984.) Bacille Calmette-Guérin vaccine
is a nonspecific stimulant of the reticuloendothelial system. It is an attenuated strain of Mycobacterium bovis that appears most effective in small,
localized bladder tumors. This agent is approved for intravesicular use in
bladder cancer. Adverse reactions are associated with the renal system,
such as problems with urination, infection, and cystitis.
BLOCK 5
Answers
5-1. The answer is e. (Cotran, p 1025.) Scrotal enlargement may be
caused by cysts, tumors, inflammatory processes, or abnormalities of the
blood vessels. Transillumination is helpful in differentiating between cysts
(which transilluminate) and tumors (which do not). Examples of the latter
include germ cell tumors and the adenomatoid tumor, a benign form of
mesothelioma that histologically is composed of glandlike or slitlike
spaces. Recall that the processus vaginalis is an outpouching of the peritoneum that enters into the scrotum. When the testis reaches the scrotum,
the proximal portion of the processus vaginalis obliterates, but the distal
portion persists and does not fuse. This forms the tunica vaginalis of the
testis. Examples of cysts that involve this tunica vaginalis include hydroceles, hematoceles, chyloceles, and spermatoceles. Hydroceles contain
clear fluid and result from developmental abnormalities or inflammatory
processes. Hematoceles result from hemorrhage into a hydrocele, while
chyloceles result from the accumulation of lymph fluid within the tunica as
a result of elephantiasis. Spermatoceles refer to cystic enlargements of the
efferent ducts or the rete testis with numerous spermatocytes present.
5-2. The answer is c. (Afifi, pp 227–230. Nolte, pp 260–262, 290–294.)
For a lesion to produce both an ipsilateral gaze paralysis and contralateral
hemiplegia, it must be situated in a location where fibers regulating both
lateral gaze and movements of the contralateral limbs lie close to each
other. The only such location is the ventrocaudal aspect of the pons, where
fibers of cranial nerve VI descend toward the ventral surface of the brainstem and where corticospinal fibers are descending toward the spinal cord.
The other regions listed in the question do not meet this condition.
5-3. The answer is c. (Cotran, pp 106–110.) Tissue repair occurs
through the regeneration of damaged cells and the replacement of tissue
by connective tissue. Tissue repair involves the formation of granulation
tissue, which histologically is characterized by a combination of prolifer253
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
254
Clinical Vignettes for the USMLE Step 1
ating fibroblasts and proliferating blood vessels. Proliferating cells are cells
that are rapidly dividing and usually have prominent nucleoli. This histologic feature should not be taken as a sign of dysplasia or malignancy. It is
important not to confuse the term granulation tissue with the similarsounding term granuloma. The latter refers to a special type of inflammation that is characterized by the presence of activated macrophages
(epithelioid cells).
5-4. The answer is e. (Braunwald, pp 1581.) The characteristics of acute
pancreatitis include nausea and vomiting, abdominal pain, low-grade
fever, and an elevated serum amylase. The pain is located primarily in the
epigastrium and radiates into the back and usually is continuous and boring in quality. Fever may or may not be present. Serum amylase and lipase
are usually elevated in the acute stages.
5-5. The answer is b. (Moore & Dalley, pp 621, 626.) The medial meniscus is attached to the medial collateral ligament. It is relatively immovable
and, therefore, unable to evade damage such as occurred in this case. The
medial meniscus is clearly not attached to the popliteus muscle or to the
anterior cruciate ligament.
5-6. The answer is 5-6-a. (Levinson, pp 302, 306, 307, 320–335.) All the
diseases listed in the question have significant epidemiologic and clinical
features. Toxoplasmosis, for example, is generally a mild, self-limiting disease; however, severe fetal disease is possible if pregnant women ingest
Toxoplasma oocysts. Consumption of uncooked meat may result in either
an acute toxoplasmosis or a chronic toxoplasmosis that is associated with
serious eye disease. Most adults have antibody titers to Toxoplasma and
thus would have a positive Sabin-Feldman dye test.
Trichinosis most often is caused by ingestion of contaminated pork
products. However, eating undercooked bear, walrus, raccoon, or possum
meat also may cause this disease. Symptoms of trichinosis include muscle
soreness and swollen eyes.
Although giardiasis has been classically associated with travel in
Russia, especially St. Petersburg (Leningrad), many cases of giardiasis
caused by contaminated water have been reported in the United States as
well. Diagnosis is made by detecting cysts in the stool. In some cases,
Block 5
Answers
255
diagnosis may be very difficult because of the relatively small number of
cysts present. Alternatively, an enzyme immunoassay may be used to detect
Giardia antigen in fecal samples.
Schistosomiasis is a worldwide public health problem. Control of this
disease entails the elimination of the intermediate host snail and removal of
streamside vegetation. Abdominal pain is a symptom of schistosomiasis.
Visceral larva migrans is an occupational disease of people who are in
close contact with dogs and cats. The disease is caused by the nematodes
Toxocara canis (dogs) and T. cati (cats) and has been recognized in young
children who have close contact with pets or who eat dirt. Symptoms
include skin rash, eosinophilia, and hepatosplenomegaly.
5-7. The answer is e. (Cotran, pp 473–475.) Hemolytic disease of the
newborn (HDN) is a type of isoimmune hemolytic anemia that is caused by
maternal antibodies that react against fetal red blood cells. Once the maternal antibodies cross the placenta, the fetal red cells are destroyed, leading
to a hemolytic anemia. The breakdown of hemoglobin leads to hyperbilirubinemia (jaundice), which is due to severe unconjugated hyperbilirubinemia, as the released heme is not easily conjugated by the immature
newborn liver, which is deficient in glucuronyl transferase. The unconjugated bilirubin is water-insoluble and has an affinity for lipids. In an infant
with a poorly developed blood-brain barrier, the bilirubin may bind to the
lipids in the brain and produce kernicterus. The severe anemia may result
in congestive heart failure, which, together with hypoproteinemia may lead
to generalized edema (anasarca), which in its most severe form is called
hydrops fetalis. In the peripheral blood of the newborn, many immature
red blood cells may be found (nucleated RBCs or normoblasts). This condition is called erythroblastosis and led to another name for HDN being
erythroblastosis fetalis.
In order for the mother to make antibodies that are directed against
fetal erythrocyte antigens, she must lack the erythrocyte antigens that the
child has, which were inherited from the father. The most important erythrocyte antigens involved in HDN are the Rh and the ABO antigens. The
most important Rh antigen is the D antigen. Therefore, for Rh incompatibility, the mother must be Rh negative (d), the child Rh positive (D). For
ABO incompatibility, the mother must be type O (lacking the A and B antigens), the child type A or B. ABO incompatibility is the most common
256
Clinical Vignettes for the USMLE Step 1
cause of hemolytic disease of the newborn. Usually the disease is less severe
than HDN due to Rh incompatibility because there is poor expression of
blood group antigens A and B on neonatal red cells.
5-8. The answer is d. (Katzung, p 969.) Cyclosporine is a peptide antibiotic that both inhibits early stages of differentiation of T cells and blocks
their activation. This most likely occurs in activated T lymphocytes by inhibition of gene transcription of immune-enhancing substances such as
interferon γ and interleukins. Cyclophosphamide, an alkylating agent,
destroys proliferating lymphoid cells. Sirolimus amarolide ab blocks the
response of T cells to cytokines. Methotrexate is an inhibitor of folic acid
synthesis. Azathioprine inhibits enzymes that are related to the biosynthesis of purines.
5-9. The answer is d. (Kandel, pp 978–980.) Vasopressin is produced
mainly from the magnocellular neurons of the hypothalamus. The hormone is released into the capillaries of the posterior pituitary. When it is
released into the vascular system, it stimulates the kidneys to conserve
water. The action of oxytocin is related to functions of the uterus and
breasts. This hormone plays a role in the expulsion of the fetus at birth and
in the milk ejection reflex following suckling. Substance P, histamine, and
somatostatin are not known to relate specifically to this process.
5-10. The answer is b. (Murray, pp 258–297. Scriver, pp 2705–2716. Sack,
pp 121–138. Wilson, pp 362–367.) Mevastatin, an analogue of mevalonic
acid, acts as a feedback inhibitor of 3′-hydroxy-3′-methylglutaryl CoA
(HMG-CoA) reductase, the regulated enzyme of cholesterol synthesis. Effective treatment with mevastatin, along with a low-fat diet, decreases levels of
blood cholesterol. The lowering of cholesterol also lowers the amounts of
the lipoprotein that transports cholesterol to the peripheral tissues, lowdensity lipoprotein (LDL). Since lipids like cholesterol and triglycerides are
insoluble in water, they must be associated with lipoproteins for transport
and salvage between their major site of synthesis (liver) and the peripheral
tissues. Those lipoproteins associated with more insoluble lipids thus have
lower density during centrifugation, a technique that separates the lowestdensity chylomicrons from very-low-density lipoproteins (VLDLs with preβ lipoproteins), low-density lipoproteins (LDLs with β-lipoproteins),
intermediate-density lipoproteins (IDLs), and high-density lipoproteins
Block 5
Answers
257
(HDLs with α-lipoproteins). Each type of lipoprotein has typical
apolipoproteins such as the apo B100 and apo B48 (translated from the
same messenger RNA) in LDL. LDL is involved in transporting cholesterol
from the liver to peripheral tissues, while HDL is a scavenger of cholesterol.
The ratio of HDL to LDL is thus a predictor of cholesterol deposition in
blood vessels, the cause of myocardial infarctions (heart attacks). The higher
the HDL/LDL ratio, the lower the rate of heart attacks.
5-11. The answer is b. (Braunwald, pp 28, 640–641.) Iron and folate deficiencies occur in pregnancy because the fetus uses these substances in large
amounts. The pregnant woman needs adequate supplements of iron and
folate. Autoantibodies and vitamin B12 are not unique causes of iron deficiency in pregnancy. The history precludes gastrointestinal bleeding and
menses as causes of this patient’s blood loss.
5-12. The answer is c. (Hardman, p 1086.) Ticarcillin resembles carbenicillin and has a high degree of potency against Pseudomonas and Proteus
organisms but is broken down by penicillinase produced by various bacteria,
including most staphylococci. Oxacillin, cloxacillin, nafcillin, and dicloxacillin are all resistant to penicillinase and are effective against staphylococci.
5-13. The answer is c. (April, pp 261–262, 273. Moore & Dalley, p 99.)
The patient has a left pneumothorax. The lucidity of the left pleural cavity
with the lack of pulmonary vessels indicates that the left lung has collapsed
into a small, dense mass adjacent to the mediastinum. Such a nontraumatic
pneumothorax may result from the rupture of a pulmonary bleb, especially
in a young person. The right lung is normal. There is no pleural fluid level
indicative of hemothorax, and the near symmetry of the domes of the two
hemidiaphragms on inspiration indicates normal function of the phrenic
nerves. The pleural cavities normally extend superior to the first rib into
the base of the neck. The heart, measuring less than one-half of the chest
diameter, is of normal size.
5-14. The answer is b. (Sierles, pp 76–80. Wedding, pp 274–275.) Contingency management is the technical term often used for positive reinforcement or stepping. It involves the process of changing the frequency of a
behavior by controlling the consequences of that behavior with positive
reinforcement to encourage or discourage a particular behavior. The proce-
258
Clinical Vignettes for the USMLE Step 1
dure is used daily in our family and professional lives, such as rewarding (or
punishing) children for their behavior and receiving (or being denied) a
raise at work. Thus, a particular behavior becomes associated with a certain
positive or negative consequence and the individual eventually accepts the
desired behavior as being preferable. Behavior therapists have developed a
wide range of applications for this learning procedure. A successful example
is the token economy program (receiving tokens redeemable for snacks,
movies, special privileges, and the like) which rewards destructive individuals for exhibiting appropriate behavior such as participating in rehabilitation activities. Contingency management has been effective with chronically
hospitalized schizophrenic patients, such as the patient in the question who
was disrupting the ward by shouting in the hall. Often, well-timed praise or
friendliness will serve as an appropriate reinforcer to foster patient compliance, as will a lollipop for a child, or a follow-up phone call to a patient who
has recovered or stopped smoking to reinforce your interest in their wellness, as well as their illness.
In stimulus control, the attempt is to eliminate the stimulus or cue that
triggers undesired behavior. Modeling exposes the individual to desirable
behavior or stimuli (e.g., posters or advertisements showing high status
persons resisting smoking or explaining how to resist peer pressure).
5-15. The answer is b. (Kandel, pp 910–918. Simon, pp 47, 258.) This
person displays a complex partial seizure, which is characterized by a confusional state with brief losses of consciousness. It is called a partial seizure
because the seizure involves a localized region, reflected by jerks of the
muscles of a specific part of the body. The focus of this seizure is typically
in the temporal lobe, such as the amygdala, hippocampal formation, or
adjoining cortical regions. A simple partial seizure does not involve loss of
consciousness. Absence seizures are nonconvulsive seizures and are also
called petit mal seizures. Generalized seizures typically involve all of the
limbs. The patient falls to the ground and loses consciousness.
5-16. The answer is c. (Howard, pp 285–286.) Except during a meningococcal epidemic, H. influenzae is the most common cause of bacterial
meningitis in children. The organism is occasionally found to be associated
with respiratory tract infections or otitis media. H. influenzae, N. meningitidis, S. pneumoniae, and Listeria account for 80 to 90% of all cases of bacterial meningitis. A purified polysaccharide vaccine conjugated to protein
Block 5
Answers
259
for H. influenzae type B is available. A tetravalent vaccine is available for
N. meningitidis and a 23-serotype vaccine for S. pneumoniae. No vaccine is
available for Listeria.
5-17. The answer is d. (Cotran, pp 1281–1283.) Duchenne’s muscular
dystrophy (DMD) is a noninflammatory inherited myopathy that causes
progressive, severe weakness and degeneration of muscles, particularly the
proximal muscles, such as the pelvic and shoulder girdles. The defective
gene is located on the X chromosome and codes for dystrophin, a protein
found on the inner surface of the sarcolemma. Histologically, muscle fibers
in patients with DMD show variations in size and shape, degenerative and
regenerative changes in adjacent myocytes, necrotic fibers invaded by histiocytes, and progressive fibrosis. There are rounded, atrophic muscle
fibers mixed with hypertrophied fibers. These muscle changes cause creatine kinase levels in the serum to be elevated. The weak muscles are
replaced by fibrofatty tissue, which results in pseudohypertrophy. In Duchenne’s muscular dystrophy, symptoms begin before the age of 4, are progressive and lead to difficulty in walking, and are eventually followed by
involvement of respiratory muscles, which causes death from respiratory
failure before the age of 20. The classification of the muscular dystrophies
is based on the mode of inheritance and clinical features. X-linked inheritance characterizes Duchenne’s muscular dystrophy, autosomal dominant
inheritance characterizes both myotonic dystrophy and the fascioscapulohumeral type, and limb-girdle dystrophy is autosomal recessive. Sustained
muscle contractions and rigidity (myotonia) are seen in myotonic dystrophy, the most common form of adult muscular dystrophy.
In contrast, dermatomyositis is an autoimmune disease that is one of a
group of idiopathic inflammatory myopathies. The inflammatory myopathies
are characterized by immune-mediated inflammation and injury of skeletal
muscle and include polymyositis, dermatomyositis, and inclusion-body
myositis. These diseases are associated with numerous types of autoantibodies, one of which is the anti-Jo-1 antibody. The capillaries are the principle
target in patients with dermatomyositis. Damage is by complement-mediated
cytotoxic antibodies against the microvasculature of skeletal muscle. In addition to proximal muscle weakness, patients typically develop a lilac discoloration around the eyelids with edema. Patients may also develop erythema
over their knuckles (Gorton’s sign). Histologically, examination of muscles
from patients with dermatomyositis reveals perivascular inflammation within
260
Clinical Vignettes for the USMLE Step 1
the tissue around muscle fascicles. This is in contrast to the other types of
inflammatory myopathies, where the inflammation is within the muscle fascicles (endomysial inflammation). In particular, inclusion-body myositis is
characterized by basophilic granular inclusions around vacuoles (“rimmed”
vacuoles). Werdnig-Hoffmann disease is a severe lower motor neuron disease
that presents in the neonatal period with marked proximal muscle weakness
(“floppy infant”).
5-18. The answer is d. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp
57–76. Wilson, pp 227–246.) This child has several minor anomalies, a major
anomaly that affects the genitalia, and developmental delay. These multiply
affected and embryologically unrelated body regions suggest a syndrome
rather than a sequence. Because of the multiple anomalies and developmental delay, the first diagnostic test to be considered is a karyotype rather
than a test for specific organ function, such as serum testosterone.
5-19. The answer is a. (Braunwald, pp 1741.) Patients with achalasia
present with a history of dysphagia or sensation of food sticking, which
includes both liquids and solids. They have a long history of these symptoms and might come for treatment at an older age.
5-20. The answer is b. (Hardman, pp 1268–1269.) Asparaginase is an
enzyme that catalyzes the hydrolysis of serum asparagine to aspartic acid
and ammonia. Major toxicities are related to antigenicity and pancreatitis.
In addition, more than 50% of those treated present biochemical evidence
of hepatic dysfunction.
5-21. The answer is a. (Braunwald, pp 244–245.) Many physicians are
concerned that there is an epidemic of obesity in the United States. One
contributing factor is the increased availability of attractive, tasty, high-fat,
high-calorie, and low-cost foods. A person does not become fat without
overeating. Furthermore, many physicians have observed that obese patients
have elevated, rather than depressed, absolute resting metabolic rates. Obesity is rarely caused by pathologic mechanisms or by disease. However, obesity does predispose an individual to disease, especially diabetes mellitus.
Obese patients are also predisposed to gallstones, degenerative joint disease,
hyperlipidemia, atherosclerosis, hypertension, sleep apnea, and some forms
of cancer.
Block 5
Answers
261
5-22. The answer is c. (Braunwald, pp 1590–1591.) Patients with hypertensive (hypercontracting) LES experience less dysphagia than patients
with esophageal spasm, and they do not complain of food sticking as do
patients with achalasia. The pain associated with hypertensive LES does
not have the characteristic of cardiac origin.
5-23. The answer is a. (Murray, pp 575–587. Scriver, pp 4077–5016. Sack,
pp 121–144. Wilson, pp 287–324.) Sex steroids are synthesized from cholesterol by side chain cleavage (employing a P450 enzyme) to produce pregnenolone. Pregnenolone is then converted to testosterone in the testis, to
estrogen in the ovary, and to corticosterone and aldosterone in the adrenal
gland. The enzymes 3β-hydroxysteroid dehydrogenase, 21-hydroxylase,
11β-hydroxylase, and 18-hydroxylase modify pregnenolone to produce
other sex and adrenal steroids. Deficiencies in adrenal 21-hydoxylase can
thus lead to inadequate testosterone production in males and produce
ambiguous external genitalia. Such children can also exhibit low sodium
and high potassium due to deficiency of the more distal steroids, cortisol
and aldosterone. 5α-reductase converts testosterone to dihydrotestosterone, and its deficiency produces milder degrees of hypogenitalism without salt wasting. Deficiency of the androgen receptor is called testicular
feminization, producing normal-looking females who may not seek medical attention until they present with infertility.
5-24 and 5-25. The answers are 5-24 d, 5-25 a. (Adams, p 280, 538.
Afifi, pp 163–168, 179–184, 209–220, 227–229. Kandel, pp 962–974.) Herb’s
drooping eyelid, small pupil, and lack of sweating on the right side are examples of Horner’s syndrome. This is caused by the interruption of sympathetic
fibers anywhere along their course from the hypothalamus and brainstem, to
the intermediolateral cell column in the upper thoracic levels of the spinal
cord where neurons, supplying sympathetic innervation to the pupil, the levator palpebrae superioris muscle of the eyelid and sweat glands of the face,
are located. Interruption of this sympathetic innervation will result in the
drooping of the upper eyelid (ptosis), pupillary constriction (miosis; due to
unopposed action of the parasympathetic innervation of the circular muscles
of the iris), and lack of sweating on the face. Parasympathetic or oculomotor
damage causes pupillary dilation, rather than constriction. Herb could close
his eyes tightly because this function is mediated by the seventh nerve, which
is not damaged by this lesion. Preganglionic sympathetic neurons are pre-
262
Clinical Vignettes for the USMLE Step 1
dominantly cholinergic, and postganglionic sympathetic neurons are predominantly noradrenergic. Horner’s syndrome may be caused by either a
preganglionic or postganglionic lesion. The location may be determined by
the use of eyedrops specifically targeted at a particular neurotransmitter. One
cause of interruption of the sympathetic fibers is a tumor of the apex (top
portion) of the lung, called a Pancoast tumor. Because the apex of the lung is
in close proximity to the spine, a Pancoast tumor may compress the upper
thoracic spinal cord where the sympathetic fibers exit from it. Compression
of the adjacent spinal nerves between C8 and T2, entering the brachial
plexus, also interrupts the nerve supply to the hand and triceps muscle, causing numbness and weakness in these areas. Pancoast tumors do not often
cause respiratory symptoms early on in their course because they are located
far from the mainstem bronchi. Because these tumors have this unique location, the neurological abnormalities often predate the respiratory problems.
The neurologist suspected that Herb may have a Pancoast tumor in the lung
because of his long history of smoking.
5-26. The answer is d. (Baum, pp 139–140.) The health risk to individuals who are in bereavement from the loss of a loved one is often ignored.
Prospective studies have shown that the stressful effects of severe life crises
are a real risk factor to general health and to the immune system. A large
cohort of middle-aged widowers demonstrated a 40% increase in their
mortality rate in the first six months of bereavement following the death of
their spouse. Furthermore, over one-half of the deaths were from cardiovascular causes. Other factors that may contribute to the increased mortality rate include sudden changes in lifestyle or environment and feelings of
isolation or lack of support.
5-27. The answer is 5-27-d. (Levinson, pp 302, 306, 307, 320–335.) All
the diseases listed in the question have significant epidemiologic and clinical features. Toxoplasmosis, for example, is generally a mild, self-limiting
disease; however, severe fetal disease is possible if pregnant women ingest
Toxoplasma oocysts. Consumption of uncooked meat may result in either
an acute toxoplasmosis or a chronic toxoplasmosis that is associated with
serious eye disease. Most adults have antibody titers to Toxoplasma and
thus would have a positive Sabin-Feldman dye test.
Trichinosis most often is caused by ingestion of contaminated pork
products. However, eating undercooked bear, walrus, raccoon, or possum
Block 5
Answers
263
meat also may cause this disease. Symptoms of trichinosis include muscle
soreness and swollen eyes.
Although giardiasis has been classically associated with travel in Russia, especially St. Petersburg (Leningrad), many cases of giardiasis caused
by contaminated water have been reported in the United States as well.
Diagnosis is made by detecting cysts in the stool. In some cases, diagnosis
may be very difficult because of the relatively small number of cysts
present. Alternatively, an enzyme immunoassay may be used to detect
Giardia antigen in fecal samples.
Schistosomiasis is a worldwide public health problem. Control of this
disease entails the elimination of the intermediate host snail and removal of
streamside vegetation. Abdominal pain is a symptom of schistosomiasis.
Visceral larva migrans is an occupational disease of people who are in
close contact with dogs and cats. The disease is caused by the nematodes
Toxocara canis (dogs) and T. cati (cats) and has been recognized in young
children who have close contact with pets or who eat dirt. Symptoms
include skin rash, eosinophilia, and hepatosplenomegaly.
5-28. The answer is a. (Murray, pp 468–487. Scriver, pp 3–45. Sack, pp
245–257. Wilson, pp 151–180.) Imbalance of globin chain synthesis occurs
in the thalassemias. Deficiency of α-globin chains (α thalassemia) is common in Asian populations and may be associated with abnormal hemoglobins composed of four β-globin chains (hemoglobin H) or (in fetuses and
newborns) of four γ-globin chains (hemoglobin Bart’s). Mutation in a transcription factor necessary for expression of α-globin could ablate α-globin
expression, since the same factor could act in trans on all four copies of the
α-globin genes (two α-globin loci). Mutation of a regulatory sequence element that acts in cis would inactivate only one α-globin gene, leaving
others to produce α-globin in reduced amounts (mild α thalassemia).
Deletions of one α-globin would produce a similar mild phenotype, and
deficiencies of transcription factors regulating α- and β-globin genes
would not produce chain imbalance.
5-29. The answer is c. (Damjanov, pp 1006–1008. Cotran, p 247,
381–382.) Infection by the protozoan P. carinii is characterized by the presence of oval and helmet-shaped organisms whose capsules are made more
visible by use of Gomori’s methenamine-silver staining technique. This
organism, although it has low virulence, is opportunistic; it is often seen to
264
Clinical Vignettes for the USMLE Step 1
attack severely ill, immunologically depressed patients. It is frequently the
first opportunistic infection to be diagnosed in HIV-1–positive patients,
and it is a leading cause of death in patients with AIDS.
5-30. The answer is d. (Levinson, pp 51–52, 68, 70, 141–142.) This question demonstrates commonly occurring clinical infectious diseases and
microbiologic problems. Enterococci may be resistant to ampicillin and
gentamicin. Vancomycin would be the drug of choice. However, laboratory
results do not always correlate well with clinical response. The National
Committee on Clinical Laboratory Standards recommends testing enterococci only for ampicillin and vancomycin.
Some symptomatic patients may have 10 leukocytes per mL of urine
but relatively few bacteria. The patient is likely infected and the organisms,
particularly if in pure culture, should be further processed.
5-31. The answer is e. (Katzung, pp 340–342.) Salmeterol is a longacting β2-adrenergic agonist that is effective in asthma prophylaxis. Skeletal muscle tremor is associated with β2-adrenergic agonists, whether short
acting or not. Other shorter-acting β2-adrenergic agonists include albuterol
and terbutaline.
5-32. The answer is c. (Cotran, pp 984–985.) A rare cause of hypertension is renal artery stenosis, which may occur secondary to either an
atheromatous plaque at the orifice of the renal artery or fibromuscular dysplasia of the renal artery. The former is more common in elderly men, while
the latter is more common in young women. The decrease in blood flow to
the kidney with the renal artery obstruction (Goldblatt’s kidney) causes
hyperplasia of the juxtaglomerular apparatus and increased renin production. This produces increased secretion of angiotensin and aldosterone,
which leads to retention of sodium and water and produces hypertension.
Increased levels of aldosterone also produce a hyperkalemic alkalosis. The
kidney with stenosis of the renal artery becomes small and shrunken due
to the effects of chronic ischemia, but the stenosis protects this kidney from
the effects of the increased blood pressure. The other kidney, however, is
not protected and may develop microscopic changes of benign nephrosclerosis (hyaline arteriolosclerosis).
5-33 and 5-34. The answers are 5-33 c, 5-34 a. (Purves, p 130. Siegel,
pp 328–332.) It has been discovered that one mechanism of neuro-
Block 5
Answers
265
degeneration involves prolonged activation of neurons by glutamate. It is
believed that if glutamate accumulates in the extracellular space and is not
removed, the presence of glutamate will effectively stimulate the neuron to
death. It has been shown that neurotoxicity is linked to cell death after a
stroke, which causes brain ischemia and oxygen deprivation. Glutamate
receptors are involved in ischemic cell damage in the following way: Glutamate released from the presynaptic terminal would normally activate
NMDA and AMPA receptors in the postsynaptic membrane. This results in
an increase in the intracellular concentration of Ca2+, which remains long
after the initial stimulus is removed, and thus prevents the cell from
reestablishing a resting membrane potential. The net effect here is to produce injury (or death) to the cell.
5-35. The answer is c. (McPhee, pp 531–539. Braunwald, pp 2106–2108.)
One of the least recognized causes of infertility in a female is scarring of the
uterus postpartum, called Asherman’s syndrome. It classically follows
curettage of the uterus, such as occurred here. Women with this syndrome
are infertile because an inability to implant. Ovarian failure, hypothyroidism, and prolactinoma are all eliminated because she still has scant regular menses. Endometriosis causes painful menses.
5-36. The answer is b. (Murray, pp 468–487. Scriver, pp 4517–4554. Sack,
pp 245–257. Wilson, pp 151–180.) Red cell hemolysis after drug exposure
suggests a red cell enzyme defect, most easily confirmed by enzyme assay
to demonstrate deficient activity. A likely diagnosis here is glucose-6phosphate dehydrogenase (G6PD) deficiency (305900), probably the most
common genetic disease (it affects 400 million people worldwide). Tropical
African and Mediterranean peoples exhibit the highest prevalence because
the disease, like sickle cell trait, confers resistance to malaria. DNA analysis is available to demonstrate particular alleles, but simple enzyme assay is
sufficient for diagnosis. More than 400 types of abnormal G6PD alleles
have been described, meaning that most affected individuals are compound heterozygotes. The phenotype of jaundice and red blood cell hemolysis with anemia is triggered by a variety of infections and drugs,
including a dietary substance in fava beans. Sulfonamide and related
antibiotics as well as antimalarial drugs are notorious for inducing hemolysis in G6PD-deficient individuals. G6PD deficiency exhibits X-linked
recessive inheritance, explaining why male offspring but not the parents
become ill when exposed to antimalarials.
266
Clinical Vignettes for the USMLE Step 1
5-37. The answer is d. (Hardman, p 1346.) A slow intravenous infusion
of protamine sulfate will quickly reverse the bleeding. Protamine binds to
heparin to form a stable complex with no anticoagulant activity. It may also
have its own anticoagulant effect by binding with platelets and fibrinogen.
5-38. The answer is b. (Moore & Dalley, pp 843–845.) The arrow points to
the sella turcica, which cradles the pituitary gland. The stalk of the gland
can be seen directly above the sella turcica. Surgically, the nasal approach to
the pituitary is through the nasal cavity, sphenoidal sinus, and the inferior
wall of the sella turcica. The other midline structures are the pharyngeal tonsil (which lies inferior to this region), and portions of the circle of Willis and
the basilar artery, which both lie within the cranial cavity.
5-39. The answer is c. (Kaplan, pp 151–152.) Systematic desensitization
was developed by Joseph Wolpe in an effort to decrease neurotic anxiety or
phobias that are learned and are usually precipitated by certain environmental situations, such as fear of heights or crowds. The patient is taught
muscular relaxation; then, while using the relaxation to inhibit the anxiety,
the patient is told to imagine a series of progressively more severe anxietyprovoking situations (e.g., climbing to the second step of a ladder, then the
fourth step, and so on) until the anxiety-provoking situation of the highest
(strongest) level can be brought to mind without the accompanying anxiety or fear. The anxiety-provoking situation is not brought to mind to be
treated by any special form of psychotherapy but becomes paired with the
anxiety-reducing relaxation. Most of these anxiety-provoking situations are
situation-specific; however, the desensitization often generalizes to other
real-life situations that may be potentially anxiety-provoking.
5-40. The answer is e. (Cotran, pp 160–163. Rubin, pp 255–257.) The
glycogen storage diseases are due to defective metabolism of glycogen,
and at least 11 syndromes stemming from genetic defects in the responsible enzymes have been described. Most of these glycogenoses are inherited as autosomal recessive disorders. von Gierke’s disease (type I) results
from deficiency of glucose-6-phosphatase, the hepatic enzyme needed for
conversion of G6P to glucose, with glycogen accumulation particularly in
the enlarged liver and kidney and hypoglycemia. Diagnosis requires
biopsy demonstration of excess liver glycogen plus either absent or low
liver glucose-6-phosphatase activity, or a diabetic glucose tolerance curve,
or hyperuricemia. von Gierke’s disease is the major hepatic or hepatorenal
Block 5
Answers
267
type of glycogenosis. Lysosomal glucosidase deficiency causes Pompe’s
disease (type II). Glycogen storage is widespread but most prominent in
the heart (cardiomegaly). In brancher glycogenosis (type IV) there is accumulation of amylopectin or abnormal glycogen in the liver, heart, skeletal
muscle, and brain. The major myopathic form, McArdle’s disease (type V),
is due to lack of muscle phosphorylase.
5-41. The answer is a. (Siegel, pp 319–321.) NMDA ion channels are
opened by both glutamate and glycine. On the other hand, Mg2 generates
a voltage-dependent block of this ion channel. The drug of abuse, phencyclidine (PCP), also utilizes a similar mechanism to block NMDA-receptor
channels. The other choices do not relate to this mechanism with respect
to PCP.
5-42. The answer is a. (Sierles, pp 182–184. Wedding, pp 184–199.) There
are a number of ways a physician can facilitate an interview, but in this case
momentary silence would be most appropriate; i.e., you should continue
to listen and perhaps offer a tissue, a nod, or a simple affirmation of understanding her import, such as “I see.” This would do more to support her by
letting her express her feelings and not interrupt her flow of thoughts with
another question or statement. Studies show that doctors tend to interrupt
a patient after about 18 seconds and that crying is very upsetting to many
doctors, who then feel compelled to say something—anything. Statements
such as “I know how you feel” are usually inappropriate because most doctors do not know how a patient feels (unless they have had a son come
home with AIDS). “Don’t worry, it’ll be OK” is a shallow response and does
not support or help the patient, as the patient realizes that the doctor does
not know that the patient will be fine. The question “Why are you so upset”
is often interpreted as an accusation or inability to understand or express
empathy. Saying “You know you can tell me anything” may be an attempt
to reassure the patient, but it is inappropriate in a new patient who does
not know that you can be told everything at this point in the relationship.
The question “Are you thinking you may have AIDS?” is an inappropriate
interruption and a very unlikely guess as to what may be upsetting the
patient. It could be appropriate later in the interview, but only after exploring many other physical and psychological factors.
5-43. The answer is b. (McPhee, p 296.) The goal for improving the
symptoms of GERD is to increase or maintain the LES pressure. High-
268
Clinical Vignettes for the USMLE Step 1
protein meals generally increase LES pressure and should be encouraged.
Fats, chocolate, and alcohol decrease LES pressure and these foods should
be avoided. Carbohydrate content does not affect motility.
5-44. The answer is b. (April, p 265.) A Pancoast tumor in the apex of
the right lung may compress the right brachiocephalic vein with resultant
venous engorgement of the right arm and right side of the face and neck.
In addition, there may be compression of the brachial artery, the sympathetic chain, and recurrent laryngeal nerve with attendant deficits. An
aneurysm of the aortic arch could reduce pulse pressures as the great vessels are occluded, but it could not explain the venous congestion.
5-45. The answer is 487-d. (McPhee, p 145. Braunwald, pp 175–179.)
Sounds must be conducted through the middle ear and sensed by the
cochlea and CN VIII; then they are processed by the cochlear nuclei and
CNS pathways. Conductive deafness is hearing loss due to external auditory canal or middle ear disease. Sensineural deafness is a perceptive loss
of hearing due to disease of the inner ear or eighth nerve. In conductive
deafness, bone conduction is better than air conduction, and the reverse is
the case for sensineural deafness. Central deafness is caused by disease
affecting the central auditory pathways. Tinnitus an annoying noise in the
ear that is usually benign, often is caused by cochlear or eighth nerve disorders. Hearing may be diminished, but the patient is not rendered fully
deaf. Presbyacusis is hearing loss due to advanced age.
5-46. The answer is c. (Conger, pp 55–68.) The growth spurt takes
approximately 41⁄2 years for both boys and girls but it normally occurs at
about age 13 for boys and at about age 11 for girls. The range is between
three to four years on either side of the average, making the variability of
growth in adolescence considerable. At age 13, Tom is probably just beginning his growth spurt, while Jill, although the same age, is a year or two
ahead of him developmentally and has already begun or reached her
menarche. This is a critical time socially and emotionally for both. Tom’s
growth spurt may have just begun while other boys in the school may be
much farther ahead, resulting in feelings of inferiority and poor selfconcept for not meeting some fantasized ideal. Jill, on the other hand, has
begun to menstruate and, like Tom, is experiencing radical changes, lowered self-concept, and even depression for fear of not “measuring up” to
Block 5
Answers
269
fantasized and media-portrayed ideals. It may be important to note that
menarche occurs about nine months earlier in girls from families with
higher incomes than from families with lower incomes.
5-47. The answer is b. (Levinson, pp 287–288.) Hairs infected with
Microsporum canis and M. audouini both fluoresce with a yellow-green color
under Wood’s light, while Trichophyton rubrum, T. tonsurans, and Epidermophyton floccosum do not. But M. audouini is an anthropophilic agent of tinea
capitis, whereas M. canis is zoophilic. M. canis is primarily seen in children
and is associated with infected cats or dogs.
5-48. The answer is d. (Cotran, pp 742, 744, 747.) Horner’s syndrome
occurs with apical (superior sulcus) tumors of any type (Pancoast tumor),
but since most peripheral cancers of the lung are adenocarcinomas, most
tumors of the apex of the lung are adenocarcinomas. Horner’s syndrome is
characterized by enophthalmos, ptosis, miosis, and anhidrosis on the same
side as the lesion due to invasion of the cervical sympathetic nerves.
Involvement of the brachial plexus causes pain and paralysis in the ulnar
nerve distribution.
5-49. The answer is a. (Cotran, pp 1304–1305. Damjanov, pp 2733–
2736.) Epidural hemorrhages result from hemorrhages into the potential
space between the dura and the bone of the skull. These hemorrhages
result from severe trauma that typically causes a skull fracture. The hemorrhage results from rupture of one of the meningeal arteries, as these arteries supply the dura and run between the dura and the skull. The artery
involved is usually the middle meningeal artery, which is a branch of the
maxillary artery, as the skull fracture is usually in the temporal area. Since
the bleeding is of arterial origin (high pressure), it is rapid and the symptoms are rapid in onset, although the patient may be normal for several
hours (lucid interval). Bleeding causes increased intracranial pressure and
can lead to tentorial herniation and death.
5-50. The answer is a. (Guyton, pp 189–190, 254–255.) The fall in blood
volume and pressure produced by hemorrhage elicits the baroreceptor
reflex. The reflex increases the activity of the sympathetic nervous system
and decreases the activity of the parasympathetic nerves innervating the
heart. Sympathetic stimulation of the smooth muscle surrounding the
270
Clinical Vignettes for the USMLE Step 1
venous vessels decreases their compliance, causing end-diastolic volume
(EDV) to increase. However, the EDV does not increase above the levels
observed prior to the hemorrhage. Heart rate, ventricular contractility, and
total peripheral resistance are all increased above their prehemorrhage levels by sympathetic stimulation. The coronary blood flow increases to meet
the increased energy requirements of the heart beating at a higher rate with
increased contractility.
BLOCK 6
Answers
6-1. The answer is d. (Simon, pp 164–168. Gilroy, pp 592–594.) In this
case, disruption of the root fibers of C5–C6 involve components of the
brachial plexus and affect muscle groups such as the deltoid, supraspinatus, intraspinatus, biceps, and flexor carpi radialis. These muscles govern
abduction of the arm, rotation of the arm at the shoulder, flexion of the
elbow and wrist. Reflex activity would also be affected due to disturbance
of both alpha and gamma motor neurons serving the biceps muscle.
Lesions involving the cerebral cortex or pons, especially the region of the
pyramidal tracts, would produce a UMN paralysis, which would include
hyperreflexia and hypertonia. An LMN paralysis involving the ventral horn
cells at C1 would not affect the brachial plexus and the muscle groups indicated in this question. The triceps muscle is not involved in producing the
movements affected by the injury.
6-2. The answer is e. (Waxman, pp 132, 150.) An MRI (magnetic resonance imaging) revealed a hemorrhage in the right subthalamic nucleus
that is interconnected with the basal ganglia. The basal ganglia participate in feedback regulation of the motor system. The basal ganglia
receive information from all regions of the cortex and project back to premotor and association cortex of the frontal lobe via the ventrolateral and
ventroanterior thalamic nuclei. A direct pathway facilitates or excites cortical motor activity, whereas an indirect pathway inhibits cortical motor
activity. Damage to the subthalamic nucleus decreases the inhibition of
excitatory relay neurons in the thalamus, thus increasing the activation of
cortical motor neurons, resulting in a characteristic form of jerky movement called ballism. Damage to an appropriate region of the cerebellum
would result in loss of fine motor control but not in ballism. Damage to
the neurons in the ventral horn of a specific level of the spinal cord
would result in a localized flaccid paralysis. The hypothalamus is
involved in vegetative functions, not voluntary movement. Damage to a
localized portion of primary sensory cortex could not be expected to
271
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
272
Clinical Vignettes for the USMLE Step 1
result in feedback deficits over both upper and lower extremities without
other neurologic deficits.
6-3. The answer is e. (McPhee, p 240. Braunwald, p 1614.) The clinical
findings in this patient are consistent with a diagnosis of Zollinger-Ellison
syndrome (multiple peptic ulcers due to a gastrin-secreting tumor). Diarrhea accompanies the symptoms of peptic ulcer frequently. The patient is a
young adult and lacks other symptoms of a gastric adenocarcinoma. Carcinoid causes diarrhea, but not often does it cause the ulcerative symptoms
this patient exhibits. Also, this patient’s symptoms are inconsistent with
lung or prostate carcinoma.
6-4. The answer is d. (Murray, pp 15–26.) Tachypnea in term infants
may result from brain injuries or metabolic diseases that irritate the respiratory center. The increased respiratory rate removes (“blows off”) carbon
dioxide from the lung alveoli and lowers blood CO2, forcing a shift in the
indicated equilibrium toward the left:
CO2 + H2O
H2CO2
H+ + HCO3−
Carbonic acid (H2CO2) can be ignored because negligible amounts are
present at physiologic pH, leaving the equilibrium:
CO2 + H2O
H+ + HCO3−
The leftward shift to replenish exhaled CO2 decreases the hydrogen ion
(H+) concentration and increases the pH (-log10[H+]) to produce alkalosis
(blood pH above the physiologic norm of 7.4). This respiratory alkalosis is
best treated by diminishing the respiratory rate to elevate the blood [CO2],
force the above equilibrium to the right, elevate the [H+], and decrease the
pH. The newborn does not have acidosis, defined as a blood pH below 7.4,
either from excess blood acids (metabolic acidosis) or from increased [CO2]
(respiratory acidosis). The baby also does not have metabolic alkalosis,
caused by loss of hydrogen ion from the kidney (e.g., with defective tubular filtration) or stomach (e.g., with severe vomiting).
6-5. The answer is e. (Cotran, pp 152–156. Rubin, pp 228–233.) Nondisjunction during the first meiotic division is responsible for trisomy 21 in
about 93% of patients with Down’s syndrome. Nondisjunction during
Block 6
Answers
273
mitosis of a somatic cell early during embryogenesis results in mosaicism
in about 2% of patients with Down’s syndrome. Translocation of an extra
long arm of chromosome 21 causes about 5% of Down’s syndrome cases.
An important type of translocation, the Robertsonian translocation (centric
fusion), involves two nonhomologous acrocentric chromosomes with the
resultant formation of one large metacentric chromosome. Carriers of this
type of translocation may also produce children with Down’s syndrome.
It is important to understand these different causes of Down’s syndrome in order to estimate the chance of recurrence if parents already have
one child with Down’s syndrome. Overall, the risk of recurrence of trisomy
21 after one such child has been born to a family is about 1%. If the karyotypes of the parents are normal, then the recurrence rate is dependent
upon the age of the mother. For mothers under the age of 30, the risk is
about 1.4%. For mothers over the age of 30, the risk is the same as the agerelated maternal risk, which at age 30 is 1/900, at age 35 is 1/350, at age
40 is 1/100, and at age 40 and over is 1/25. The recurrence risk is different
for a translocation Down’s syndrome, which may be either a 14q21q
Robertsonian translocation or a 21q21q translocation. A carrier of a
Robertsonian translocation involving chromosomes 14 and 21 has only 45
chromosomes and can theoretically produce six possible types of gametes.
Of these, only three are potentially viable: one that is normal, one that is
balanced, and one that is unbalanced, having both the translocated chromosome and a normal chromosome 21. The latter, when combined with a
normal gamete, could produce a child with Down’s syndrome. Therefore,
theoretically, the risk of a carrier of this type of Robertsonian translocation
producing a child with Down’s syndrome would be 1 in 3. In practice,
about 15% of the progeny of mothers with this type of translocation, and
very few of the progeny of fathers with this type of translocation, develop
Down’s syndrome. In contrast, carriers of a 21q21q translocation produce
gametes that either have the translocated chromosome or lack any 21 chromosome. Progeny then can have either trisomy 21 or monosomy 21, but,
since the latter is rarely viable, approximately 100% of progeny will have
Down’s syndrome.
6-6. The answer is a. (Howard, pp 791–796.) Epstein-Barr virus (EBV) is
a herpesvirus that causes a number of syndromes; the most common is
infectious mononucleosis. It is a ubiquitous enveloped DNA virus. Only
one serotype of EBV has been recognized, although molecular methods
have reorganized a number of genotypes of EBV.
274
Clinical Vignettes for the USMLE Step 1
Infectious mononucleosis is an acute disease most commonly seen in
younger people. It is characterized by a proliferation of lymphocytes,
lymph node enlargement, pharyngitis, fatigue, and fever. Infection in
young children is usually either asymptomatic or characteristic of an acute
upper respiratory infection. Diagnosis is usually made by a positive heterophil test. Heterophil antibodies are those that occur in one species
(human) and react with antigens of a different species. The heterophil test
may be insensitive (30 to 60%) in children. Definitive diagnosis is made by
detection of antibodies to EBV components.
EBV causes a variety of other syndromes including Burkitt’s lymphoma, the most common childhood cancer in Africa, and nasopharyngeal
carcinoma, commonly seen in China.
Similar mononucleosis-like diseases are caused by cytomegalovirus
(CMV) and Toxoplasma gondii, a parasite. CMV causes fewer than 10% of
infectious mononucleosis-like diseases. CMV “mono” is primarily characterized by fatigue. Congenital infection with CMV almost always causes
serious sequelae, such as retardation and hearing loss. T. gondii also causes
a variety of clinical problems, among them encephalitis in AIDS patients
and food poisoning from the ingestion of raw meat. Although CMV and T.
gondii are relatively rare causes of infectious mononucleosis, they must be
ruled out, particularly when EBV tests are nonreactive.
6-7. The answer is e. (Nolte, pp 488–492.) Since the flocculonodular
lobe receives and integrates inputs from the vestibular system, it is understandable why lesions that disrupt this integrating mechanism for vestibular inputs would result in difficulties in maintaining balance. Indeed, this is
a classic feature of lesions of the flocculonodular lobe but is not associated
with lesions in the hemispheres of the posterior lobe, anterior limb of the
internal capsule, or the dentate nucleus, which are functionally linked to
the frontal lobe. Lesions of the anterior lobe also do not affect mechanisms
of balance.
6-8. The answer is e. (Hardman, p 1533.) Enthusiastic overmedication
with vitamin D may lead to a toxic syndrome called hypervitaminosis D. The
initial symptoms can include weakness, nausea, weight loss, anemia, and
mild acidosis. As the excessive doses are continued, signs of nephrotoxicity are manifested, such as polyuria, polydipsia, azotemia, and eventually
nephrocalcinosis. In adults, osteoporosis can occur. Also, there is CNS
impairment, which can result in mental retardation and convulsions.
Block 6
Answers
275
6-9. The answer is b. (Braunwald, pp 253–255, 1664.) CT scan is very
helpful in evaluating obstructive jaundice, particularly when a pancreatic
source is suspected. For subtle lesions for which the differential diagnosis
includes metastatic disease, vascular problems, or parenchymal disease,
MRI is very helpful if the CAT scan is not diagnostic. An upper abdominal
ultrasound is the ideal test to examine the gallbladder for stones, and a barium swallow is the initial study favored in the evaluation of patients with
dysphagia. A KUB might show an enlarged liver, but contribute to the evaluation of jaundice, especially when the pancreas is involved.
6-10. The answer is b. (Levinson, pp 51–52, 68, 70, 141–142.) These
questions demonstrate commonly occurring clinical infectious diseases
and microbiologic problems. Enterococci may be resistant to ampicillin
and gentamicin. Vancomycin would be the drug of choice. However, laboratory results do not always correlate well with clinical response. The
National Committee on Clinical Laboratory Standards recommends testing
enterococci only for ampicillin and vancomycin.
Some symptomatic patients may have 10 leukocytes per mL of urine
but relatively few bacteria. The patient is likely infected and the organisms,
particularly if in pure culture, should be further processed.
6-11. The answer is e. (Murray, pp 375–401. Scriver, pp 2663–2704.
Sack, pp 121–138. Wilson, pp 287–320.) Orotic aciduria is the buildup of
orotic acid due to a deficiency in one or both of the enzymes that convert
it to UMP. Either orotate phosphoribosyltransferase and orotidylate
decarboxylase are both defective, or the decarboxylase alone is defective.
UMP is the precursor of UTP, CTP, and TMP. All of these end products
normally act in some way to feedback-inhibit the initial reactions of
pyrimidine synthesis. Specifically, the lack of CTP inhibition allows
aspartate transcarbamoylase to remain highly active and ultimately
results in a buildup of orotic acid and the resultant orotic aciduria. The
lack of CTP, TMP, and UTP leads to a decreased erythrocyte formation
and megaloblastic anemia. Uridine treatment is effective because uridine
can easily be converted to UMP by omnipresent tissue kinases, thus
allowing UTP, CTP, and TMP to be synthesized and feedback-inhibit further orotic acid production.
6-12. The answer is a. (Cotran, pp 1314–1317.) Meningitis [inflammation of the arachnoid and the cerebrospinal fluid (CSF)], may be classified
276
Clinical Vignettes for the USMLE Step 1
as acute pyogenic, aseptic, or chronic. The etiology and CSF findings vary
in these three groups. The CSF in acute pyogenic meningitis, which is
usually caused by bacteria, is grossly cloudy (not bloody, which is suggestive of a subarachnoid hemorrhage) and displays increased pressure,
increased neutrophils, increased protein, and decreased glucose. With
chronic meningitis, such as that caused by Mycobacterium tuberculosis, the
CSF is clear grossly, with only a slight increase in leukocytes (either
mononuclear cells or a mixed infiltrate), a markedly increased protein
level, increased pressure, and moderately decreased or normal amounts of
sugar. Both brain abscesses and subdural empyemas, which are parameningeal infections rather than direct meningeal infections, cause
increased CSF pressure (more marked with abscess because of mass effect)
along with increased inflammatory cells (lymphocytes and polys) and
increased protein but a normal glucose level. The CSF is clear. Encephalitis, also not a direct infection of the meninges, results in clear CSF,
increased pressure, increased protein, normal glucose, and possibly
increased lymphocytes.
6-13. The answer is b. (April, p 57.) The horizontal direction of the
fibers of the clavicular head of the pectoralis major muscle draws the
humerus medially and causes the distal fragment of the bone to sublux.
The sternal head of this muscle also has the effect of pulling the arm medially, an effect that is normally offset by the strutlike action of the clavicle.
6-14. The answer is d. (April, p 65.) Because large and important neurovascular structures pass between the clavicle and first rib, including the
subclavian artery, clavicular fracture may produce life-threatening bleeding
into the pleural cavity. The axillary artery is the continuation of the subclavian after it has cleared the first rib, so neither this vessel nor its thoracoacromial branch is likely to be threatened by clavicular fracture. There is
no brachiocephalic artery on the left side, and on the right its terminal
point is marked by its bifurcation into common carotid and subclavian
arteries proximal to the fracture site.
6-15. The answer is c. (Levinson, pp 147–148.) The serologic diagnosis of
Lyme disease is fraught with difficulty. Enzyme immunoassay (EIA) may be
insensitive in the early stages of disease and may lack specificity in advanced
stages. Western blot analysis of antibody is the confirmatory test for Lyme
Block 6
Answers
277
disease, but it, too, is not 100% sensitive and specific. The Western blot test
detects antibodies to proteins and glycoproteins of Borrelia burgdorferi. Not
all of these proteins are specific for the organism. For example, antibodies to
Gp66 may reflect a cross-reaction, as many Gram-negative bacteria have
similar glycoproteins. For this reason, a Western blot showing only antibodies to Gp66 is thought to be a nonspecific immune response.
6-16. The answer is b. (Cotran, pp 766–767. Rubin, pp 1331–1333.)
Ménière’s disease is an abnormality that is characterized by periodic
episodes of vertigo that are often accompanied by nausea and vomiting,
sensorineural hearing loss, and tinnitus (ringing in the ears). These symptoms are related to hydropic dilation of the endolymphatic system of the
cochlea. Inflammation of the middle ear (otitis media), which occurs most
often in children, may be acute or chronic. If otitis media is caused by
viruses, there may be a serous exudate, but if it is produced by bacteria,
there may be a suppurative exudate. Acute suppurative otitis media is characterized by acute suppurative inflammation (neutrophils), while chronic
otitis media involves chronic inflammation with granulation tissue.
Chronic otitis media may cause perforation of the eardrum or may lead to
the formation of a cyst within the middle ear that is filled with keratin,
called a cholesteatoma. The name is somewhat of a misnomer, as cholesterol deposits are not present. Otosclerosis, a common hereditary cause of
bilateral conduction hearing loss, is associated with formation of new
spongy bone around the stapes and the oval window. Patients present with
progressive deafness. Tumors of the middle ear are quite rare, but a neoplasm that arises from the paraganglia of the middle ear (the glomus jugulare or glomus tympanicum) is called a chemodectoma. Other names for
this tumor include nonchromaffin paraganglioma and glomus jugulare
tumor. This lesion is characterized histologically by lobules of cells in a
highly vascular stroma (zellballen). A similar tumor that occurs in the neck
is called a carotid body tumor.
6-17. The answer is d. (Hardman, p 1481.) Of the glucocorticoids listed,
dexamethasone is the most potent. The dexamethasone suppression test has
several uses—it allows not only complete suppression of pituitary ACTH
production, but also accurate measurement of endogenous corticosteroids
such as 17-ketosteroids in the urine. The small amount of dexamethasone
present contributes minimally to this measurement.
278
Clinical Vignettes for the USMLE Step 1
6-18. The answer is d. (Howard, p 457.) Helicobacter pylori was first recognized as a possible cause of gastritis and peptic ulcer by Marshall and
Warren in 1984. This organism is readily isolated from gastric biopsies but
not from stomach contents. It is similar to Campylobacter species and grows
on chocolate agar at 37°C in the same microaerophilic environment suitable
for C. jejuni (Campy-Pak or anaerobic jar [Gas Pak] without the catalyst).
H. pylori, however, grows more slowly than C. jejuni, requiring 5 to 7 days
incubation. C. jejuni grows optimally at 42°C, not 37°C, as does H. pylori.
6-19. The answer is e. (Cotran, pp 447–448. Chandrasoma, pp 160–162.
Rubin, pp 348–349.) Vitamin B1 (thiamine) has three important functions. It
participates in oxidative decarboxylation of α-keto acids; participates as a
cofactor for transketolase in the pentose phosphate path; and participates
in maintaining neural membranes. The causes of thiamine deficiency
include poor diet, deficient absorption and storage, and accelerated
destruction of thiamine diphosphate. This deficiency may be seen in alcoholics and prisoners of war because of poor nutrition, or it may be seen in
individuals who eat large amounts of polished rice. (Polishing rice removes
the outer, thiamine-containing portion of the grain.) Thiamine deficiency
(called beriberi) mainly affects two organ systems, the heart and the nervous system. If the heart is affected in a patient with beriberi, it may
become dilated and flabby. Patients may also develop peripheral vasodilation that leads to a high-output cardiac failure and marked peripheral
edema. This combination of vascular abnormalities is called wet beriberi.
The peripheral nerves in beriberi may be damaged by focal areas of myelin
degeneration, which leads to footdrop, wristdrop, and sensory changes
(numbness and tingling) in the feet and lower legs. These symptoms are
referred to as dry beriberi. Thiamine deficiency may produce the central
nervous system (CNS) symptoms of Wernicke-Korsakoff syndrome. Wernicke’s encephalopathy consists mainly of foci of hemorrhages and necrosis in the mammillary bodies and about the ventricular regions of the
thalamus and hypothalamus, about the aqueduct in the midbrain, and in
the floor of the fourth ventricle. Symptoms of Wernicke’s syndrome include
progressive dementia (confusion), ataxia, and paralysis of the extraocular
muscles—often with bilateral lateral rectus, or sixth nerve, palsies (ophthalmoplegia). Korsakoff psychosis is a thought disorder that produces retrograde memory failure and confabulation.
Block 6
Answers
279
In contrast to niacin, biotin (vitamin H) is an important cofactor for
multisubunit enzymes that catalyze carboxylation reactions, an example of
which is the synthesis and oxidation of fatty acids. A deficiency of biotin
can lead to multiple symptoms, including depression, hallucinations, muscle pain, and dermatitis. Biotin is present in dietary food and is also produced by intestinal bacteria. Deficiencies of biotin are quite rare, but can
occur in people who consume raw eggs. This is because egg white contains
a heat-labile protein, avidin, which combines very tightly with biotin and
prevents the absorption of biotin. Pyridoxine is a cofactor that participates
in transamination reactions, decarboxylation reactions, and transsulfuration reactions. It is important in the synthesis of GABA and d-ALA. Deficiencies of pyridoxine can lead to decreased synthesis of GABA, which can
cause convulsions in infants or a polyneuropathy in adults, or decreased
ALA, which produces a hypochromic, sideroblastic anemia. Patients also
develop cheilosis (inflammation and fissuring of the lips), angular stomatitis (cheilosis occurring at the corners of the mouth), glossitis (atrophy of
the mucosa of the tongue), and seborrheic dermatitis. Pyridoxine deficiency may result from pregnancy or therapy with certain drugs, such as
isoniazid, methyldopa, or levodopa. A common cause of B6 deficiency is
chronic alcoholism. A deficiency of riboflavin (vitamin B2) is characterized
by changes that occur around the mouth, namely cheilosis, angular stomatitis, and glossitis. Additionally, patients may develop seborrheic dermatitis of the face or genitalia, or blindness, which is the result of
vascularization of the cornea (interstitial keratitis). Selenium is an antioxidant that is part of glutathione peroxidase, an enzyme that is found in red
cells and white cells. As such, it prevents oxidative damage to both red
blood cells and white cells. A deficiency of selenium leads to a form of
dilated cardiomyopathy in children. This deficiency has been described in
China and is called Keshan disease.
6-20. The answer is a. (Hardman, pp 1086–1089.) Intolerance of alcohol
(disulfiram-like reaction) has been noted only with certain cephalosporins.
Cephalosporins with the methylthiotetrazole side chain have been associated
with a disulfiram-like reaction because the methylthiotetrazole group has a
configuration similar to disulfiram, which blocks the metabolism of alcohol
at the acetaldehyde step. Accumulation of acetaldehyde is associated with the
symptoms. The methylthiotetrazole side chain also results in hypoprothrom-
280
Clinical Vignettes for the USMLE Step 1
binemia by interfering with the synthesis of vitamin K–dependent clotting
factors.
6-21. The answer is c. (Braunwald, p 1705.) Acute alcoholic hepatitis is
characterized by the presence of Mallory bodies and WBCs in the liver
biopsy specimen. Frequently, it shows fat and degenerating cells in the
liver. Usually, with abstinence from alcohol, this will revert to a normal histologic pattern. However, on occasion, liver disease can progress despite
abstinence.
6-22. The answer is b. (Hazzard, pp 1036–1037.) Alzheimer’s disease is a
progressive, disabling, degenerative disease and the most common cause of
dementia in the elderly. The most common presenting feature of Alzheimer’s
disease is loss of memory. It is also usually accompanied by a gradual decline
in intellectual function and impairment of orientation to time and place,
judgment, problem solving, language, perception, and learning. Personality
change often involves alteration or accentuation of premorbid traits, delusions, apathy, or depression.
6-23. The answer is a. (Hardman, pp 1247–1251.) 5-Fluorouracil is a
pyrimidine antagonist that has a low neurotoxicity when compared with
other fluorinated derivatives; however, its major toxicities are myelosuppression and oral or gastrointestinal ulceration. Leukopenia is the most frequent clinical manifestation of the myelosuppression.
6-24. The answer is d. (Afifi, pp 211, 227–231.) Inability to move the
eyes up or down when they are displaced laterally would result from a
lesion of the midbrain involving cranial nerve III. Because the somatomotor neurons of cranial nerve III supply, in part, the superior and inferior
recti muscles as well as the inferior oblique muscle, cranial nerve III is
responsible for up-and-down movements of the eye when they are positioned laterally. Recall that when the eye is positioned medially, it is the
superior oblique that is innervated by cranial nerve IV that pulls the eye
downward.
6-25. The answer is e. (Levinson, pp 150–152.) Ornithosis (psittacosis) is
caused by Chlamydia psittaci. Humans usually contract the disease from
Block 6
Answers
281
infected birds kept as pets or from infected poultry, including poultry in
dressing plants. Although ornithosis may be asymptomatic in humans,
severe pneumonia can develop. Fortunately, the disease is cured easily with
tetracycline.
6-26. The answer is e. (Carpenter, pp 174–175. Noback, p 209.) The
abducens nerve (CN VI) innervates the lateral rectus muscle. Loss of innervation to the lateral rectus results in unopposed tension by the medial rectus, which produces internal strabismus. The oculomotor nerve (CN III)
innervates the medial, superior, and inferior recti, the inferior oblique, and
the levator palpebrae superioris muscles. Paralysis of this nerve would
result in lateral deviation of the eye (external strabismus) accompanied by
ptosis (drooping eyelid). In addition, mydriasis (dilated pupil) results from
loss of function of the parasympathetic component of the oculomotor
nerve. Damage to the trochlear nerve (CN IV) results in paralysis of the
superior oblique muscle with impaired ability to direct the eye downward
and outward.
6-27. The answer is d. (Katzung, pp 589–590.) Only gemfibrozil acts to
lower triglycerides, probably because of increased lipolysis by lipoprotein
lipase and decreased lipolysis inside adipocytes, causing a net movement of
triglycerides into the cell.
6-28. The answer is b. (Kaplan, pp 361–362.) Hyperthyroidism (thyrotoxicosis) is a syndrome resulting from a chronic excess of thyroid hormone (thyroxine). It may be precipitated by acute emotional stress and
may even develop within hours after an emotional trauma. It is an
endocrine disorder and is almost always accompanied by mental
changes—the patient may feel tense and hyperexcitable and may be emotionally labile, with inappropriate temper outbursts, crying spells, or
euphoria. Distractibility, short attention span, and impaired recent memory
may also be present. Severe hyperthyroidism may result in frank psychosis,
delirium, coma, and death. Thyroid disorders are 7 times more frequent in
women than in men; they occur most commonly in women in their third
and fourth decades and in men at older ages. In contrast to the tense and
hyperexcitable behaviors usually observed, a minority of patients, particularly the elderly, may be depressed, apathetic, and anorectic with chronic
282
Clinical Vignettes for the USMLE Step 1
hyperthyroidism. Mildly hyperthyroid patients occasionally are misdiagnosed as having anxiety neuroses. Mental retardation in children is frequently associated with hypothyroidism, not hyperthyroidism, since normal
brain development requires the thyroid hormone.
6-29. The answer is b. (Kandel, pp 82–83, 700–704.) In a peripheral neuropathy, there may be damage to either the myelin or the axon directly,
although, more often, there is damage to the myelin. Because of myelin (or
axonal) damage, there is a reduction (or loss) of conduction velocity. The
disorder may affect both sensory and motor components of the peripheral
nerve, thereby causing dysfunction in both the sensory and the motor
processes associated with that nerve. Because there is peripheral neuronal
damage, the motor loss will be reflected in a weakness, paralysis, or reflex
activity associated with the affected muscle, as well as impairment of sensation.
6-30. The answer is b. (Guyton, pp 241–243.) The most obvious deleterious effect of a failing heart is the inability to pump enough blood to satisfy
the energy requirements of all the tissues. Among the compensatory mechanisms that develop in response to heart failure is an increase in retention of
fluid by the kidney. Increased retention of fluid causes the end-diastolic volume of the heart to increase, which, by the Starling mechanism, increases
the strength of the heartbeat. However, two deleterious effects result from an
increase in end-diastolic volume. A larger than normal end-diastolic volume
causes an increase in end-diastolic pressure, which can lead to pulmonary
edema. In addition, the large end-diastolic volume increases the wall stress
that must be developed by the heart with each beat, and this increases the
myocardial requirement of oxygen. The increase in contractility that results
from the administration of a positive inotropic drug such as digoxin will
allow the heart to produce the same force at a lower volume and thus eliminate the need for an increase in volume of fluid.
6-31. The answer is d. (Levinson, pp 75–77.) Recurrent severe infection
is an indication for clinical evaluation of immune status. Live vaccines,
including BCG attenuated from Mycobacterium tuberculosis, should not be
used in the evaluation of a patient’s immune competence because patients
with severe immunodeficiencies may develop an overwhelming infection
Block 6
Answers
283
from the vaccine. For the same reason, oral (Sabin) polio vaccine is not
advisable for use in such persons.
6-32. The answer is a. (Katzung, p 499.) Of the listed antidepressants,
only amitriptyline, a tricyclic, causes adverse effects related to blockade of
muscarinic acetylcholine receptors. Both trazodone and amitriptyline
cause adverse effects related to α-adrenoreceptor blockade.
6-33. The answer is d. (McPhee, p. 140; Braunwald, pp 2460–2468.)
Numerous localized disorders and many systemic diseases can damage
the spinal cord or the peripheral nerves. The pattern of pain, sensory
loss, and sometimes weakness can help classify the disorder. A mononeuropathy involves pain/temperature and vibratory/joint position abnormalities, along the precise path of an individual nerve with associated
weakness and pain. Mononeuropathy multiplex involves multiple noncontiguous peripheral nerves in a sequential fashion taking place over
days to years. A radiculopathy involves a nerve root with dermatome distribution of both pain/temperature and vibratory/joint position abnormalities and weakness of the innervated muscles. Brown-Séquard’s
syndrome also involves pain/temperature and vibratory/joint position
abnormalities; however, the distribution is ipsilateral pain/temperature
and contralateral vibratory/joint position abnormalities with an ipsilateral motor deficit. A polyneuropathy similarly involves pain/temperature
and vibratory/joint position abnormalities with a stocking-glove distribution and painful paraesthesias.
6-34. The answer is e. (Howard, pp 213–242.) Many sputum specimens
are cultured unnecessarily. Sputum is often contaminated with saliva or is
almost totally made up of saliva. These specimens rarely reveal the cause of
the patient’s respiratory problem and may provide laboratory information
that is harmful. The sputum in question appears to be a good specimen.
The pleomorphic Gram-negative rods are suggestive of Haemophilus, but
culture of the secretions is necessary.
6-35. The answer is a. (Cotran, pp 926–928.) Functional islet cell tumors
of the pancreas secrete specific substances that result in several syndromes.
Pancreatic gastrinomas (tumors of the G cells of the pancreas) secrete gas-
284
Clinical Vignettes for the USMLE Step 1
trin and are a cause of Zollinger-Ellison syndrome. This syndrome consists
of intractable gastric hypersecretion, severe peptic ulceration of the duodenum and jejunum, and high serum levels of gastrin. The majority of gastrinomas are malignant. Insulinomas (tumors of β cells) are the most
common islet cell neoplasm and are usually benign. Symptoms include low
blood sugar, hunger, sweating, and nervousness. Glucagonomas (islet cell
tumors of the α cells) secrete glucagon and are characterized by mild diabetes, anemia, venous thrombosis, severe infections, and a migratory,
necrotizing, erythematous skin rash. δ cell tumors, which secrete somatostatin, produce a syndrome associated with mild diabetes, gallstones, steatorrhea, and hypochlorhydria. The majority of δ cell tumors are malignant.
D1 tumors [also called vasoactive intestinal peptide tumors (VIPomas)]
produce Verner-Morrison syndrome, which is characterized by explosive,
profuse diarrhea with hypokalemia and hypochlorhydria. This combination of symptoms is referred to as pancreatic cholera.
6-36. The answer is b. (Murray, pp 627–661. Scriver, pp 3127–3164. Sack,
pp 121–138. Wilson, pp 287–320.) Ferrous iron (Fe++) is the form absorbed in
the intestine by ferritin, transported in plasma by transferrin, and stored in
the liver in combination with ferritin or as hemosiderin. There is no known
excretory pathway for iron, either in the ferric or ferrous form. For this reason, excessive iron uptake over a period of many years may cause hemochromatosis (235200), the likely diagnosis for this man. This is a condition of
extensive hemosiderin deposition in the liver, myocardium, pancreas, and
adrenals. The resulting symptoms include liver cirrhosis, congestive heart
failure, diabetes mellitus, and changes in skin pigmentation.
6-37. The answer is b. (McPhee, pp 548–549. Braunwald, pp 2092–2095.)
Mumps virus infection can directly affect the testicles, producing an orchitis, often very painful, and consequently infertility. Posttesticular causes are
those that affect sperm transport, and pretesticular causes are those that
affect the hormones that stimulate the testicles.
6-38. The answer is b. (Hardman, p 1077.) Oxacillin is classified as a
penicillinase-resistant penicillin that is relatively acid-stable and, therefore,
is useful for oral administration. Major adverse reactions include penicillin
hypersensitivity and interstitial nephritis. With the exception of methicillin, which is 35% bound to serum proteins, all penicillinase-resistant
Block 6
Answers
285
penicillins are highly bound to plasma proteins. Oxacillin has a very narrow spectrum and is used primarily as an antistaphylococcal agent.
6-39 through 6-40. The answers are 6-39 c, 6-40 b. (Kandel, pp
298–304. Gilroy, pp 623–639, 640–642. Siegel, pp 871–883.) Myasthenia
gravis is an autoimmune disease that causes cranial nerve and limb muscle weakness by producing antibodies that act against the nicotinic receptor at the neuromuscular junction. The result is that the action of nerve
fibers that innervate skeletal muscle are affected, producing loss of the
effects of ACh at the neuromuscular junction. The net result is a reduction
of the size of the action potential in the muscle, producing a weakness in
the affected muscle. This disorder is reversed by administration of drugs
that inhibit the enzyme, acetylcholinesterase, that degrades ACh. Multiple
sclerosis, ALS, and combined system disease (see the chapter entitled “The
Spinal Cord”) involve damage to axons and/or nerve cells within the CNS,
producing much more profound damage to motor functions and, in the
case of combined system disease, damage to both motor and sensory systems. Muscular dystrophy is typically characterized, in part, by progressive weakness of muscles and degeneration of the muscle fibers. The other
disorders listed all involve disorders affecting the CNS, and thus, the
symptoms associated with these disorders differ significantly from those
described in this case. Excessive release of ACh is not a realistic event that
is likely to occur (except from the bite of a black widow spider). In theory,
if it were to occur, there is no reason to believe that muscular weakness
would be a symptom. Instead, there would be some rigidity and muscle
spasms.
6-41. The answer is c. (Murray, pp 468–487. Scriver, pp 175–192. Sack, pp
245–257. Wilson, pp 151–180.) After the locus responsible for a genetic disease is mapped to a particular chromosome region, “candidate” genes can
be examined for molecular abnormalities in affected individuals. The connective tissue abnormalities in Stickler syndrome (108300) make the
COL2A1 collagen locus an attractive candidate for disease mutations,
prompting analysis of COL2A1 gene structure and expression. Western
blotting detects gene alterations that interfere with protein expression,
while use of the reverse transcriptase–polymerase chain reaction (RT-PCR)
detects alterations in mRNA levels. Each analysis should detect one-half
the respective amounts of COL2A1 protein or mRNA in the case of a pro-
286
Clinical Vignettes for the USMLE Step 1
moter mutation that abolishes transcription of one COL2A1 allele. Southern blotting detects nucleotide changes that alter DNA restriction sites, but
this is relatively insensitive unless large portions of the gene are deleted.
Fluorescent in situ hybridization (FISH) analysis using DNA probes from
the COL2A1 locus is a sensitive method for detecting deletions of the entire
locus, and DNA sequencing of the entire gene provides the gold standard
for detecting any alteration in the regulatory or coding sequences.
Nucleotide sequence changes are still subject to interpretation, since they
may represent polymorphisms that do not alter gene function. Population
studies and/or in vitro studies of gene expression are often needed to discriminate DNA polymorphisms from mutations that disrupt gene function.
For any autosomal locus, the interpretation of molecular analyses is complicated by the presence of two homologous copies of the gene.
6-42. The answer is e. (April, p 613.) The patient has facial paralysis,
which indicates injury to the facial nerve. A problem in the internal auditory
meatus usually affects hearing and balance. That the superior salivatory
nucleus is normal is indicated by normal lacrimation. Hence, the lesion
must be distal to the origin of the greater superficial nerve at the genu of the
facial nerve. However, absence of hyperacusis indicates that the branch to
the stapedius muscle is functioning normally, and this fact suggests that the
lesion is close to the stylomastoid foramen. Loss of taste and diminished
salivation locate the lesion proximal to the origin of the chorda tympani
nerve. If the lesion were distal to the stylomastoid foramen, taste and salivation would have been normal with facial paralysis as the only sign.
6-43. The answer is a. (Cotran, pp 961–962.) Many diseases involve
hematuria, and a few of these diseases occur in the setting of an upper respiratory infection or of upper respiratory signs and symptoms. When hematuria follows within 2 days of the onset of an upper respiratory infection
without skin lesions in a young patient, IgA nephropathy (Berger’s disease)
should be considered. This disease involves the deposition of IgA in the
mesangium of the glomeruli. Light microscopic examination may suggest
the disease, but renal biopsy immunofluorescence (IF) must be performed
to confirm it. This disorder may be the most common cause of nephritic
syndrome worldwide. The hematuria may become recurrent, with proteinuria that may approach nephrotic syndrome proportions. Serum levels of
IgA may be elevated. A small percentage of patients may progress to renal
failure over a period of years. In contrast to Berger’s disease, a linear IF pat-
Block 6
Answers
287
tern suggests a type II hypersensitivity reaction, such as Goodpasture’s disease, while a granular pattern is seen with post-streptococcal glomerulonephritis (GN), membranous GN, focal segmental glomerulosclerosis,
and membranoproliferative GN. Most positive immunofluorescence patterns involve IgG and C3, except that a granular IgM pattern is present in
focal segmental glomerulosclerosis, while mesangial IgA is seen in IgA
nephropathy (Berger’s disease). Lipoid nephrosis would have a negative IF
pattern; that is, there would be no staining present.
6-44. The answer is e. (Hardman, pp 1269–1271.) Cisplatin causes
acoustic nerve damage. Paclitaxel causes peripheral neuritis. Dosedependent pneumonitis and fibrosis are caused by bleomycin. Doxorubicin causes cardiac toxicity, which may lead to congestive heart failure.
5-Fluorouracil causes myelosuppression, stomatitis, and oral and gastrointestinal ulcerations.
6-45. The answer is b. (Levinson, pp 147–148, 153–155.) All the listed
diseases except Q fever are tick-borne. The rickettsia C. burnetii causes
Q fever, and humans are usually infected by aerosol of a sporelike form
shed in milk, urine, feces, or placenta of infected sheep, cattle, or goats.
Lyme disease is caused by a spirochete, Borrelia burgdorferi, and produces
the characteristic lesion erythema chronicum migrans (ECM). The etiologic agent of Rocky Mountain spotted fever is R. rickettsia. It usually produces a rash that begins in the extremities and then involves the trunk.
Two human forms of ehrlichiosis can occur: human monocytic ehrlichiosis (HME), caused by E. chaffeensis; and human granulocytic ehrlichiosis
(HGE), caused by an as yet unnamed Ehrlichia. Ehrlichiosis was previously recognized only as a veterinary pathogen. HME infection is transmitted by the brown dog tick and A. americanum. HGE infection is
transmitted by I. scapularis, the same tick that transmits Lyme disease.
Both infections cause fever and leukopenia. A rash rarely occurs. E. chaffeensis infects monocytes, and HGE infects granulocytes; both organisms
produce inclusion bodies called morulae. Francisella tularensis is a small,
Gram-negative, nonmotile coccobacillus. Humans most commonly acquire
the organism after contact with tissues or body fluid of an infected mammal or the bite of an infected tick.
6-46. The answer is b. (Cotran, pp 394–396. Rubin, pp 475–476.) Intestinal tapeworm (cestode) infections result from eating improperly prepared
288
Clinical Vignettes for the USMLE Step 1
meat. T. saginata is acquired from ingesting contaminated beef, T. solium is
acquired from contaminated pork, and D. latum is obtained from contaminated fish. The life cycles of these tapeworms involve larval stages in animals and worm stages in humans. If the contaminated meat contains the
larval forms of these organisms, then they may develop into adult worms in
the intestines of infected humans. These individuals generally remain
asymptomatic, except that D. latum may cause a vitamin B12 deficiency. A
very different disease results from humans eating the eggs of T. solium,
which may be found in human feces. In this case, the eggs hatch into larva,
which then penetrate the gut wall and disseminate via the bloodstream to
lodge in different organs. There they encyst and differentiate into cysticerci.
Multiple cysticerci in the brain produce a “Swiss cheese” appearance
grossly, and microscopically a scolex (the head of the worm) is found with
hooklets. This disease is called cysticercosis. Another cestode, E. granulosa,
is the cause of hydatid disease in humans. Individuals become infected by
eating the tapeworm eggs. Patients are usually sheep herders who get the
eggs from their dogs. Larvae released from the eggs disseminate most often
to the liver (75%), but they may also travel to the lungs or skeletal muscle.
They form large, slowly growing, unilocular cysts that contain multiple
scolices. Toxocara species, such as T. canis and T. cati, are one cause of visceral larval migrans. This disease is characterized by infection of visceral
organs by helminthic larvae. The typical patient is a young child who
develops hypereosinophilia and hypergammaglobulinemia. Ocular manifestations of toxocariasis are common, especially the loss of vision in one
eye in a child. Note that this disease is different from cutaneous larva
migrans, which is caused by the larval forms of the hookworms and
Strongyloides stercoralis.
6-47. The answer is a. (Braunwald, p 1699.) The most serious consequences of chronic hepatitis B and C infections are hepatoma and cirrhosis. Complications of cirrhosis may occur, resulting in liver failure. Chronic
hepatitis is not a risk factor for adenoma, cholangitis, lymphoma, or hemochromatosis.
6-48. The answer is c. (McPhee, pp 548–549. Braunwald, pp 2092– 2095.)
Posttesticular causes of infertility are those that affect sperm transport, such
as penile anatomic defects including hypospadias and epispadias. Other
posttesticular causes of infertility include genital tract infections, retro-
Block 6
Answers
289
grade ejaculation, and antibodies to sperm or seminal plasma. Pretesticular
causes are those that affect the hormones that stimulate the testicles, and
testicular causes are those with a direct effect on the testicles. Idiopathic
causes represent those causes that are likely genetic and not elsewhere classified.
6-49. The answer is e. (Cotran, pp 1333–1334.) The degenerative diseases of the CNS are diseases that affect the gray matter and are characterized by the progressive loss of neurons in specific areas of the brain. In
Parkinson’s disease, characterized by a masklike facial expression, coarse
tremors, slowness of voluntary movements, and muscular rigidity, there is
degeneration and loss of pigmented cells in the substantia nigra, resulting
in a decrease in dopamine synthesis. Lewy bodies (eosinophilic intracytoplasmic inclusions) are found in the remaining neurons of the substantia
nigra. The decreased synthesis of dopamine by neurons originating in the
substantia nigra leads to decreased amounts and functioning of dopamine
in the striatum. This results in decreased dopamine inhibition and a relative increase in acetylcholine function, which is excitatory in the striatum.
The effect of this excitation, however, is to increase the functioning of
GABA neurons, which are inhibitory. The result, therefore, is increased
inhibition or decreased movement. The severity of the motor syndrome
correlates with the degree of dopamine deficiency. Therapy may be with
dopamine agonists or anticholinergics.
6-50. The answer is b. (Levinson, pp 145–147.) This patient appears to
have primary syphilis as evidenced by a penile chancre that was not tender.
One of the differences between syphilis and herpes simplex virus (HSV) is
that an HSV lesion is excruciatingly painful. Treponemal organisms may be
seen microscopically in the lesion if the lesion is scraped. If not treated, the
chancre will disappear and the patient will be asymptomatic until he/she
exhibits the signs/symptoms of secondary syphilis, which include a disseminated rash and systemic involvement such as meningitis, hepatitis, or
nephritis. There are two kinds of tests for the detection of syphilis antibodies: nonspecific tests such as the RPR and VDRL, and specific tests such as
the FTA, TPHA (Treponema pallidum hemagglutination test), and the
MHTP (microhemagglutination-T. pallidum). The difference is that the
nonspecific tests use a cross-reactive antigen known as cardiolipin, while
the specific tests use a T. pallidum antigen. Although the nonspecific tests
290
Clinical Vignettes for the USMLE Step 1
are sensitive, they lack specificity and often cross-react in patients who
have diabetes, hepatitis, infectious mononucleosis, or who are pregnant.
Some patients, especially those with autoimmune diseases, will have both
nonspecific (RPR) and specific tests (FTA) positive. Resolution of such a situation can be done by molecular methods for T. pallidum such as PCR, or
by the immobilization test using live spirochetes and the patient’s serum. In
the TPI test, the spirochetes will die in the presence of specific antibody.
BLOCK 7
Answers
7-1. The answer is a. (Cotran, p 176.) Sexual ambiguity arises when
there is disagreement between the various ways of determining sex.
Genetic sex is determined by the presence or absence of a Y chromosome.
Gonadal sex is based upon the histologic appearance of the gonads. Ductal
sex depends on the presence of derivatives of the Müllerian or Wolffian
ducts. Phenotypic or genital sex is based on the appearance of the external
genitalia. True hermaphroditism refers to the presence of both ovarian and
testicular tissue. Pseudohermaphroditism is a disagreement between the
phenotypic and gonadal sex. A female pseudohermaphrodite has ovaries
but external male genitalia, while a male pseudohermaphrodite has testicular tissue, resulting from an XY genital sex karyotype, but female external
genitalia. Female pseudohermaphroditism results from excessive exposure
to androgens during early gestation; most often this is the result of congenital adrenal hyperplasia. Male pseudohermaphroditism results from
defective virilization of the male embryo, most commonly caused by
complete androgen insensitivity syndrome, also called testicular feminization.
Kallmann’s syndrome results from a lack of embryonic migration of
cells from the olfactory bulb to the hypothalamus and is characterized by
primary amenorrhea, lack of secondary sex characteristics, and decreased
sense of smell (hyposmia). Laboratory findings include decreased GnRH,
LH, and FSH. Mixed gonadal dysgenesis consists of one well-defined testis
and a contralateral streak ovary. It is a cause of ambiguous genitalia in the
newborn. Turner’s syndrome, which has a 45,XO karyotype, is characterized by a female phenotype and bilateral streak ovaries.
7-2. The answer is d. (Levinson, pp 153–155.) Most rickettsial diseases
are transmitted to humans by way of arthropod vectors. The only exception
is Q fever, which is caused by C. burnetii. This organism is transmitted by
inhalation of contaminated dust and aerosols or by ingestion of contaminated milk.
291
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
292
Clinical Vignettes for the USMLE Step 1
7-3. The answer is b. (Brust, p 246.) The middle cerebral artery supplies
a large portion of cerebral cortex, including portions of the frontal, parietal,
and temporal lobes. These regions include the Broca’s and Wernicke’s areas
and the precentral motor and postcentral sensory regions. Decreased blood
flow in these regions explains the observed motor and sensory deficits. The
anterior choroidal artery is a branch of the internal carotid artery and is primarily distributed to the basal ganglia, hippocampus, and choroid plexus
of the lateral ventricle. The posterior communicating artery connects the
internal carotid and vertebral arterial systems. The ophthalmic artery is a
direct branch of the internal carotid artery that enters the orbit along with
the optic nerve. Although the anterior cerebral artery has a wide distribution and anastomoses with branches of both the middle and posterior cerebral arteries, it primarily supplies medial and superior portions of the
cortex.
7-4. The answer is d. (Simon, pp 163–164.) In this case, there is a loss of
superficial abdominal reflexes, which require that spinal segments T8–T12
are intact. The test for these reflexes is to stroke a quadrant of the abdominal wall with an object such as a wooden stick. The normal response is for
the muscle of the quadrant stimulated to contract and for movement of the
umbilicus in the direction of the stimulus.
7-5. The answer is a. (Cotran, p 1129.) Both oligodendroglioma and
craniopharyngioma show calcification fairly frequently; oligodendroglioma
is often located in the frontal lobe, whereas craniopharyngioma occurs
around the third ventricle and demonstrates suprasellar calcification. CT
scan and particularly MRI are essential in diagnosis. Patchy intracerebral
calcification may develop in tuberous sclerosis, an autosomal dominant
disease characterized by the triad of epilepsy, mental retardation, and facial
skin lesions (multiple angiofibromas). In addition, subependymal gliosis,
cardiac rhabdomyoma, renal angiomyolipoma, and periungual fibroma
occur. Calcification of the basal ganglia occurs in about 20% of patients
with chronic hypoparathyroidism, which sometimes leads to a Parkinsonian syndrome.
7-6. The answer is c. (Braunwald, p 1688.) The serologic pattern in this
case is a person who has recovered from HBV infection. They possess antiHBs, the protective antibody in HBV infection, IgG anti-HBc, and anti-
Block 7
Answers
293
HBc. The anti-HBc may be positive or negative in persons who recover
from HBV.
7-7. The answer is c. (Hardman, p 810.) Digitalis inhibits Na+,K+-ATPase
and, hence, decreases myocyte Na pumping, resulting in a relative reduction of Ca expulsion from Na-Ca exchange. The consequent increase in free
Ca in the cell causes an increased intensity of interaction between actin and
myosin filaments and enhanced contractility.
7-8. The answer is c. (Levinson, pp 143–144.) The symptoms of Legionnaires’ disease are similar to those of mycoplasmal pneumonia and
influenza. Affected persons are moderately febrile, complain of pleuritic
chest pain, and have a dry cough. Unlike Klebsiella and Staphylococcus,
Legionella pneumophila exhibits fastidious growth requirements. Charcoal
yeast extract agar either with or without antibiotics is the preferred isolation medium. While sputum may not be the specimen of choice for
Legionella, the discovery of small Gram-negative rods by direct fluorescent
antibody (FA) technique should certainly heighten suspicion of the disease.
L. pneumophila is a facultative intracellular pathogen and enters macrophages without activating their oxidizing capabilities. The organisms bind
to macrophage C receptors, which promote engulfment.
7-9. The answer is b. (Moore & Dalley, p 15.) The flexor pollicis brevis
has two heads and there is a sesamoid bone associated with each of the tendons of these heads. Sesamoid bones are isolated islands of bone that may
occur in tendons passing over joints. The patella is the classic example. The
adductor pollicis also has two heads (transverse and oblique), but they are
not associated with sesamoid bones.
7-10. The answer is d. (Braunwald, p 77.) This syndrome is called
pseudoclaudication. It may also occur at times with exertion, thus causing
confusion with peripheral vascular disease. Nerve impingement by osteoarthritis and by degenerative disk disease tends to give a radicular pattern
to the discomfort.
7-11. The answer is d. (Baum, pp 220–221.) Temporomandibular disorder (TMD) involves pain in the oral cavity and grinding of the teeth. It
affects either the jaw and/or the muscles in the face, head, neck, and shoul-
294
Clinical Vignettes for the USMLE Step 1
ders. Anxiety and depression are major causal links in promoting grinding
of the teeth both during the day and at night. This action produces chronic
pain even without the jaw moving or the teeth grinding. The physiologic or
neurologic etiology is still not clear, but studies have estimated that
between one-third and one-half of the general population suffers from
TMD. Less than 5% of these sufferers seek medical attention. Emotional
factors such as depression, anxiety, distress, and sensitivity to pain are particularly important in developing and maintaining the chronic pain. Psychosocial efforts to reduce the stress and depression show moderate
success, as have dental and general pain clinics where patients are educated
about the disorder and taught behavioral techniques to relax and reduce
the pain, through biofeedback. Psychosocial therapy has also been successfully combined with selected antidepressants to help reduce TMD.
7-12. The answer is a. (Cotran, pp 805–811.) The causes of diarrhea are
numerous, and diarrhea may be broadly classified into multiple categories
including secretory, osmotic, and exudative. Both secretory and exudative
diarrhea may have infectious causes. Several viruses may cause secretory
diarrhea. Rotavirus is a major cause of diarrhea in children between the
ages of 6 and 24 months. Clinical symptoms consisting of vomiting and
watery (secretory) diarrhea begin about 2 days after exposure. Bacterial
enterocolitis may be related to either the production of performed toxins,
such as with Vibrio cholerae and enterotoxigenic E. coli (a major cause of
“traveler’s diarrhea”), or it may be related to bacterial invasion of the colon,
as seen with salmonella and shigella. E. histolytica is a cause of amebiasis
and is endemic in underdeveloped countries. It characteristically produces
flask-shaped ulcers in the colon and may embolize to the liver, where it
produces amebic liver abscesses. Lactase deficiency, a cause of osmotic
diarrhea, is very rarely a congenital disorder, but much more commonly is
an acquired disorder seen in adults that results in malabsorption of milk
and milk products. The onset of symptoms from ulcerative colitis is most
commonly apparent between the ages of 20 and 25 years.
7-13. The answer is d. (Hazzard, pp 125–141, 154, 177–184.) A major
problem in attempting to provide health care for the elderly is understanding and counteracting some of the common stereotypes of aging. Although
it is generally true that all five senses tend to decline in old age, it is not true
that most elderly people feel miserable most of the time. In fact, recent
Block 7
Answers
295
studies show that the majority of the aged see themselves as being as happy
as they were when they were younger. Boredom and lack of meaningful
activity do become major factors with some aged, however. Another misconception is that a high percentage of the aged population live in longstay institutions, such as nursing homes, mental hospitals, and homes for
the aged. Actually, only about 5% of persons 65 and over, and about 10%
of persons age 75 and over, are in long-stay institutions. Attempting to
retain one’s social, physical, and cognitive independence is a dominating
factor and priority among the aged. Also, contrary to the stereotype that
older drivers have a high automobile accident rate, older drivers have
about the same accident rate per person as middle-aged drivers and a lower
rate than drivers under age 30. By age 85, however, the crash rate is
highest per mile driven. Longitudinal research has demonstrated that personality traits are highly stable after about age 30.
7-14. The answer is e. (Adams, pp 246–247.) In one form of retinitis pigmentosa, there is a genetic defect with respect to rhodopsin. The result of
this defect is the production of defective opsin. As a consequence, rod cells
are affected, leading to a reduced response to light. However, central vision
is spared as are cone cells. Central nervous system (CNS) neurons such as
those located in area 17 are not directly affected and vision is not totally lost.
7-15. The answer is c. (Murray, pp 627–661. Scriver, pp 3897–3964. Sack,
pp 121–138. Wilson, pp 287–320.) Hemorrhagic disease of the newborn is
caused by poor transfer of maternal vitamin K through the placenta and by
lack of intestinal bacteria in the infant for synthesis of vitamin K. The intestine is sterile at birth and becomes colonized over the first few weeks.
Because of these factors, vitamin K is routinely administered to newborns.
Deficiencies of the fat-soluble vitamins A, E, D, and K can occur with
intestinal malabsorption, but avid fetal uptake during pregnancy usually
prevents infantile symptoms. Hypervitaminosis A can cause liver toxicity
but not bleeding, and deficiencies of E (neonatal anemia) or C (extremely
rare in neonates) have other symptoms besides bleeding.
7-16. The answer is d. (Ryan, p 115.) The initial response to a new infection is with an IgM class antibody. IgM develops quickly and usually disappears within a few months. The secondary response is IgG and reflects the
patient’s immune status or, in the case of chickenpox, a vaccination given.
296
Clinical Vignettes for the USMLE Step 1
7-17. The answer is b. (Sierles, pp 292–296. Wedding, pp 260–265.) The
husband in the question is using a strong denial mechanism of defense. In
the early stages of alcohol abuse denial often involves not recognizing the
obvious problem. It soon becomes a major defense reaction, especially as
the person begins to recognize within himself that his own attempts to control or resolve the alcohol problem are woefully inadequate, nor can he
control some of the underlying psychosocial problems. Initial rationalization soon turns into strong denial. It is somewhat analogous to smoking
addiction when a smoker rationalizes that she can quit any time she wants,
and then begins to realize she can’t. Unfortunately in cases of alcohol
abuse, the spouse usually waits an average of seven years after gross evidence of alcoholic behavior before seeking help. This puts the physician
tremendously behind in attempting to help the patient, the family, or the
community. In many medical schools very little is taught about substance
abuse. Consider the denial being exercised in the medical school setting.
While only 5% of medical students smoke cigarettes, 80% use alcohol at
least twice weekly, and 16% consume an average of more than six drinks
each time, also known as binge drinking.
Other options in the question include rationalization (unacceptable
feelings or facts become more tolerable by explaining them away), projection (attributing your own unacceptable thoughts or feelings to someone
else), displacement (redirecting an emotion from the original object to
another one), and reaction formation (adopting an attitude or behavior that
is the opposite of your own unconscious feelings).
7-18. The answer is c. (Katzung, pp 778–780.) Clarithromycin is a
macrolide antibiotic. It can inhibit cytochrome P450. This could lead to
an increase in concentration of drugs that are metabolized by cytochrome
P450 and are given simultaneously with clarithromycin. When given with
terfenadine, an antihistaminic agent, the interaction may lead to cardiac
arrhythmias.
7-19. The answer is a. (Brust, pp 210–213.) The nucleus ambiguus,
along with special visceral efferent (SVE) components of CN IX, X, and XI,
is a column of lower motor neurons that innervate muscles of the pharynx,
larynx, and palate. Damage to this nucleus results in loss of the gag reflex,
difficulty in swallowing, and hoarseness.
The lateral spinothalamic tract passes through the medulla and carries
Block 7
Answers
297
sensory information (pain and temperature) from the contralateral extremities and trunk. Similarly, the spinal tract of CN V carries pain and temperature sensation from the ipsilateral face. Descending sympathetic pathways
course through the medulla to reach the intermediolateral cell column of
the spinal gray matter. Damage to these fibers would result in loss of ability to dilate the pupil (meiosis), drooping eyelid (ptosis), and loss of sweating ipsilaterally (hemianhydrosis). Damage to nerve fibers passing to and
from the cerebellum via the inferior cerebellar peduncle would result in
intention tremor and lack of coordination.
7-20. The answer is a. (Sierles, pp 94–97.) The most powerful biopsychosocial predictor of prevalence of illness and morbidity and mortality
rates is socioeconomic status (SES). Persons of lower SES have a significantly higher prevalence of obesity, chronic illnesses, hypertension, and
coronary artery disease. This can be attributed to multiple factors, including lack of access to medical care, lack of resources to seek medical care,
living and working in a high-risk environment, dietary deficiencies, lack of
educational background, lack of responsiveness of physicians to patients of
lower SES and their problems, and the general lack of societal and political
concern with the health of the poor. Iatrogenic illness is not as frequent in
persons of lower SES because they have less contact with the remedies of
physicians and medical technology.
7-21. The answer is c. (Cotran, pp 336, 379–380. Rubin, pp 436–438.)
Cryptococcosis is caused by Cryptococcus neoformans, an encapsulated
yeast (not dimorphic) that infects the central nervous system, primarily in
immunocompromised patients. The soil-dwelling yeast is inhaled, but lung
involvement tends to be mild in individuals who are not immunodeficient.
Diagnosis of cryptococcal meningitis is achieved by finding encapsulated
yeasts in CSF preparations. The capsule can be seen with a mucicarmine
stain, or it can be negatively stained using india ink. The CSF and serum
should also be tested for cryptococcal antigen by the latex cryptococcal
agglutination test (LCAT), which is positive in more than 90% of cases.
Cryptococcal meningitis varies from a chronic inflammatory and granulomatous infection to a noninflammatory meningitis with numerous yeasts
massed, sometimes forming cystic “soap bubble” lesions in the brain. Do
not confuse cryptococcus with cryptosporidium. Cryptosporidium parvum
is a protozoan parasite that may cause a transient diarrhea in immunocom-
298
Clinical Vignettes for the USMLE Step 1
petent individuals or a chronic diarrhea in patients with AIDS (cryptosporidiosis). Histologically, sporozoites may be found attached to the surface of intestinal epithelial cells. They are best seen with an acid-fast stain.
Chromomycosis is a chronic infection of the skin that is produced by
an organism that appears as a brown, thick-walled sphere (“copper penny”)
in tissue sections. Coccidioidomycosis is a mycotic infection caused by
inhalation of the arthrospores of the dimorphic fungus C. immitis. Within
the lung the spores enlarge to form large spherules (sporangia) that become
filled with many small endospores. The cyst ruptures, releasing the
endospores. Unruptured spherules incite a granulomatous reaction, while
the endospores cause a neutrophilic response. Paracoccidioidomycosis
(South American blastomycosis) is a chronic granulomatous infection
caused by Paracoccidioides brasiliensis, a dimorphic fungus seen in tissues as
a large central organism having peripheral oval budding. This histologic
appearance is described as being similar to a mariner’s wheel.
7-22. The answer is c. (Hardman, pp 813–814.) Digoxin is used in AF to
slow the ventricular rate, not usually the AF itself. Digoxin acts to slow the
speed of conduction, increase the atrial and AV nodal maximal diastolic
resting membrane potential, and increase the effective refractory period in
the AV node, which prevents transmission of all impulses from the atria to
the ventricles. It exerts these effects by acting directly on the heart and by
indirectly increasing vagal activity.
7-23. The answer is 7-23-c. (Howard, pp 535–537, 754, 755, 789–791.)
Borrelia burgdorferi, the causative agent of Lyme disease, elicits an acute antibody response. IgM appears within days to a few weeks following tick bite,
and IgG appears a few weeks later. IgG persists, IgM does not. Crossreactions occur with other treponemes.
Fifth disease is a viral exanthem commonly seen in children 8 to 12
years old. Children are ill for a few days but recover without incident.
Unfortunately, if a pregnant female acquires the disease in the first trimester
of pregnancy, the fetus is at risk. The causative agent is thought to be a parvovirus (parvovirus B 19).
Adults with no titer to varicella (VZV) are at risk for acquisition of
chickenpox. If they are health care workers, there is additional risk in transmitting VZV to immunodeficient children. Antibodies to VZV are readily
detected by both enzyme immunoassay (EIA) and fluorescent-antibody
(FA) techniques.
Block 7
Answers
299
Delta agent is a recently discovered antigen associated with HBsAg. Its
presence usually correlates with HBsAg chronic carriers who have chronic
active hepatitis. EIA and radioimmunoassay (RIA) tests are available to
detect antibodies to delta agent.
SSPE is thought to be caused by a measles-related virus present in the
central nervous system. Most SSPE patients show elevated measles virus
antibodies in serum and CSF. In patients with multiple sclerosis (MS),
lower CSF antibody titers have been observed, suggesting a possible etiologic role for measles virus in MS.
7-24. The answer is e. (Cotran, pp 904–907.) Inflammation of the pancreas (pancreatitis) may be either acute or chronic. Patients with acute pancreatitis typically present with abdominal pain that is associated with
increased serum levels of pancreatic enzymes (amylase and lipase). Most
cases of acute pancreatitis are associated with either alcohol ingestion or biliary tract disease (gallstones). Alcohol ingestion is the most common cause,
and pancreatitis usually follows an episode of heavy drinking. Other, less
frequent causes include hypercalcemia, hyperlipidemias, shock, infections
(CMV and mumps), trauma, and drugs. Acute pancreatitis usually presents
as a medical emergency. Symptoms of acute pancreatitis include abdominal
pain that is localized to the epigastrium and radiates to the back, vomiting,
and shock, the latter being the result of hemorrhage and kinins released into
the blood. In severe pancreatitis there may be hemorrhage in the subcutaneous tissue around the umbilicus (Cullen’s sign) and in the flanks (Turner’s
sign). Activation of the plasma coagulation cascade may lead to disseminated intravascular coagulopathy (DIC). Laboratory confirmation of pancreatic disease involves the finding of elevated serum amylase levels in the
first 24 h and rising lipase levels over the next several days. Other pancreatic enzymes, such as trypsin, chymotrypsin, and carboxypeptidases, have
not been as useful for diagnosis as have amylase and lipase. Complications
seen in patients who survive the acute attack include pancreatic abscess formation, pseudocyst formation, or duodenal obstruction. Diabetes mellitus
almost never occurs after a single attack of pancreatitis.
7-25. The answer is a. (Kingsley, pp 436–439; Purves, pp 225–227.) In
astigmatism, the shapes of the cornea and possibly the lens become oblong,
resulting in differences in the curvature of the lens along the long and short
axes. Thus, astigmatism is corrected with a cylindrical lens.
300
Clinical Vignettes for the USMLE Step 1
7-26. The answer is d. (Hardman, pp 1475–1476.) The incidence of
adverse reactions with administration of prednisone is related to dosage
and duration. Psychoses, peptic ulceration with or without hemorrhage
(possibly leading to guaiac-positive stools), increased susceptibility to
infection, edema, osteoporosis, myopathy, and hypokalemic alkalosis can
occur. Other adverse reactions include cataracts, hyperglycemia, arrest of
growth in children, and iatrogenic Cushing’s syndrome. The glucocorticoids are very effective drugs, but they can be very dangerous if not properly administered to a patient.
7-27. The answer is a. (Cotran, pp 14–15, 846–848.) The type and distribution of necrotic hepatocytes is often a clue as to the cause of the hepatic
injury. Focal scattered necrosis is characteristic of viral hepatitis, but may
also be seen with bacterial infections or other toxic insults. In focal necrosis,
there is necrosis of single hepatocytes, or small clusters of hepatocytes, that
is randomly located in some, but not all, of the liver lobules. In contrast,
zonal necrosis refers to the finding of hepatocellular necrosis in identical
areas in all of the liver lobules. There are basically three types of zonal necrosis. Centrilobular (acinar zone 3) necrosis is characteristic of ischemic injury
(heart failure or shock), toxic effects (acetaminophen toxicity), carbon tetrachloride exposure, or chloroform ingestion. Drugs such as acetaminophen
may be metabolized in zone 1 to toxic compounds that cause necrosis of
zone 3 hepatocytes because they receive the blood from zone 1. Midzonal
(zone 2) necrosis is quite rare, but may be seen in yellow fever, while periportal (zone 1) necrosis is seen in phosphorus poisoning or eclampsia. Submassive necrosis refers to liver cell necrosis that crosses the normal lobular
boundaries. Classically the necrosis goes from portal areas to central veins
(or vice versa) and is called bridging necrosis. If the hepatocellular necrosis
is severe, it is called massive necrosis. This type of extensive necrosis is
described as acute yellow atrophy, as grossly the liver appears soft, yellow,
flabby, and decreased in size with a wrinkled capsule. It may be produced
by hepatitis viruses (usually B or C), drugs, or chemicals.
7-28. The answer is a. (Guyton, p 440.) Beta-receptor-activated G proteins activate adenyl cyclase which catalyzes the formation of cAMP. cAMP
activates protein kinase A, which phosphorylates phospholamban. Phosphorylated phospholamban releases the SR Ca2+ pump from inhibition. The
sequestration of Ca2+ into the SR relaxes bronchiolar smooth muscle. In car-
Block 7
Answers
301
diac muscle, the sequestration of Ca2+ into the SR increases contractile
strength because there is more Ca2+ available for release with each action
potential. The depolarization of the SA node is caused by activation of the
“funny” channel. This channel is activated at negative membrane potentials.
The rate of its activation is increased when it is phosphorylated by protein
kinase A. The transport of Ca2+ into skeletal muscle fibers is not affected by
beta-receptors. Glycogenolysis in the liver is also increased by activated
beta-receptors. In this case, the protein kinase A phosphorylates an enzyme
called phosphorylase, which begins the process of glycogenolysis.
7-29. The answer is a. (Katzung, pp 697–698.) Mifepristone is structurally
related to norethindrone. This compound is classified as a progesterone antagonist with weak agonistic properties. A single dose can function as an emergency postcoital contraceptive. It also can induce an abortion by causing
contraction of the myometrium, which leads to detachment of the embryo.
The drug is used in single or multiple doses followed by the administration of
a prostaglandin to cause the abortion. Estrogens used alone or in combination
with progestins have also proven effective in postcoital contraception.
7-30. The answer is c. (Levinson, pp 133–134.) Pasteurella multocida, a
coccobacillary Gram-negative rod, is part of the normal mouth flora of
dogs and cats. Consequently, many animal bites become infected with this
microorganism. It is susceptible to penicillin, although multiresistant
strains have been recovered from pigs and sheep. P. multocida has four different capsular types—designated A, B, D, and E—that correlate with disease production and host predilection; however, serotyping of these
isolates is beyond the resources of most laboratories.
7-31. The answer is e. (Murray, pp 468–487. Scriver, pp 175–192. Sack, pp
245–257. Wilson, pp 151–180.) Gene therapy refers to a group of techniques
by which gene structure or expression is altered to ameliorate a disease.
Because of ethical and practical difficulties, germ-line therapy involving
alterations of genes in primordial germ cells is not being explored in
humans. Although germ-line genetic engineering is being performed in
animals with the goals of improved breeding or agricultural yield, it alters
the characteristics of offspring rather than the treated individuals. Somatic
cell gene therapy is targeted to an affected tissue or group of tissues in the
individual, and is most effective if stem cells such as bone marrow can be
302
Clinical Vignettes for the USMLE Step 1
treated. Somatic cell gene therapy offers the hope of replacing damaged tissue without the rejection problems of transplantation. For autosomal recessive disorders, only one of the two defective alleles must be replaced or
supplemented.
7-32. The answer is e. (Simon, pp 138–145.) Fibers from the left lateral
geniculate destined for the upper bank of the calcarine fissure will mediate
visual impulses associated with lower quadrants of the right visual fields
for both eyes. This deficit is referred to as a right lower quadrantanopia.
7-33. The answer is d. (Sierles, p 405. Baum, pp 60–106.) While fearfulness, confusion, interpersonal conflict, and regression can generate stress
that can have a direct effect on biologic responses, the loss of perceived control can take an even greater toll on the body. Excessive workload and job
responsibility are stressful factors in terms of coronary risk, but they become
even more powerful and biologically more destructive when they approach
the limit of a person’s capacity to control his or her own work. Whether the
stress is from employment, unemployment, finance, family, disease, or other
factors, the threat of loss or actual loss of control over one’s being or activities appears to be the most devastating influence. Different people also have
considerable variability in their responsiveness to a lack of or loss of control;
this responsiveness then has a subsequent effect on their biologic processes.
7-34. The answer is c. (Guyton, pp 846–853.) Radiation treatment likely
produced panhypopituitarism in the young child. Sexual maturation and
growth during development will not occur because of low levels of GH,
FSH, LF, ILGF1, TSH and thyroid hormones, and gonadal hormones. The
cortisol response to stress is decreased due to low ACTH levels. A goiter
cannot develop in the absence of TH.
7-35. The answer is a. (Hardman, pp 1460, 1464.) Cosyntropin is related
to adrenocorticotropin. It corresponds to the first 24 amino acids of adrenocorticotropin. Cosyntropin complexes with a plasma membrane receptor
that brings about the activation of adenylyl cyclase. Adenylyl cyclase catalyzes the formation of cAMP from ATP. In the cytoplasm, cAMP activates
cAMP-dependent protein kinase, which participates in the phosphorylation
of specific substrate proteins (e.g., enzymes). The phosphorylated protein
eventually induces the particular response on the target cell.
Block 7
Answers
303
The cellular mechanism of action of hydrocortisone, a glucocorticoid,
is also related to proteins but not by the enhancement of cAMP production.
Hydrocortisone is transported by simple diffusion across the membrane of
the cell into the cytoplasm and binds to a specific receptor. The steroidreceptor complex is activated and enters the nucleus, where it regulates
transcription of specific gene sequences into ribonucleic acid (RNA). Eventually, messenger RNA (mRNA) is translated to form specific proteins in the
cytoplasm that are involved in the steroid-induced cellular response.
7-36. The answer is b. (Moore & Dalley, pp 189, 350–351.) Flexion of the
thigh would be least affected. The lesion involves the common iliac artery
just proximal to its division into the internal and external iliac branches.
Blood flow would be compromised to the external iliac artery and its
downstream branches including the femoral, deep femoral, popliteal, tibial, fibular, and plantar arteries. Blood flow would also be diminished to
branches of the internal iliac artery, including gluteal and visceral arteries.
One of the most powerful flexors of the thigh is the psoas muscle, which
originates from the lumbar vertebrae and receives most of its blood from
the aorta and common iliac artery and thus would be unaffected by the
lesion.
7-37. The answer is f. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp
1–40. Wilson, pp 23–98.) It is important that the pedigree be an accurate
reflection of the family history and that information not be recorded unless
specifically mentioned. Pedigree B in the figure omits the double line
needed to indicate consanguinity, and pedigree C assumes that the father’s
affected cousin is the offspring of his uncle rather than being unspecified.
Pedigree F correctly illustrates the birth order (third) of the affected female
(indicated by arrow) and the consanguinity (double line) represented by
the first-cousin marriage.
7-38. The answer is c. (Braunwald, pp 2265, 2504–2505.) Alcohol withdrawal seizures are suspected because the man became shaky 2 days after
admission in the hospital where he would not have access to alcoholic beverages, he has a macrocytosis consistent with folate deficiency due to alcoholism, and the diagnostic tests showed no underlying neurologic disease.
The consumption of alcohol leads to excessive loss of magnesium in the
urine and thus lowers seizure threshold. The AST level in general will
304
Clinical Vignettes for the USMLE Step 1
increase more in the face of alcohol usage than will the ALT. The bulk of
alcohol withdrawal seizures will occur within 5 days of the cessation of
alcohol consumption.
7-39. The answer is b. (Braunwald, p 1688.) In this case, the patient has
acute HBV infection signaled by the positive IgM anti-HBC. Because the
HBsAg is negative, it likely is below the threshold for detection. The IgM
response reflects recent infection. This serologic pattern does not fit with
infection with any of the other hepatitis viruses. The symptoms and signs,
lack of fever, and minimal abnormal findings on examination of the liver
are consistent with the diagnosis of acute HBV.
7-40. The answer is d. (Hardman, pp 1080–1082. Katzung, pp 759–760.)
Because of its long duration of action, benzathine penicillin G is given as a
single injection of 1.2 million units intramuscularly every three or four
weeks for the treatment of syphilis. This persistence of action reduces the
need for repeated injections, costs, and local trauma. Benzathine penicillin
G is also administered for group A, β-hemolytic streptococcal pharyngitis
and pyoderma. For the later stages of syphilis, up to three weekly doses of
the agent is administered.
7-41. The answer is d. (Murray, pp 505–626. Scriver, pp 4029–4240.
Sack, pp 121–138. Wilson, pp 287–320.) Leukotrienes C4, D4, and E4
together compose the slow-reacting substance of anaphylaxis (SRS-A),
which is thought to be the cause of asphyxiation in individuals not
treated rapidly enough following an anaphylactic shock. SRS-A is up to
1000 times more effective than histamines in causing bronchial muscle
constriction. Anti-inflammatory steroids are usually given intravenously
to end chronic bronchoconstriction and hypotension following a shock.
The steroids block phospholipase A2 action, preventing the synthesis of
leukotrienes from arachidonic acid. Acute treatment involves epinephrine injected subcutaneously initially and then intravenously. Antihistamines such as diphenhydramine are administered intravenously or
intramuscularly.
7-42. The answer is c. (Simon, pp 173–183.) The most likely cause of the
condition in this patient is a cervical disk prolapse. This disorder would
produce pain in the neck and arm, which increases with movement of the
Block 7
Answers
305
head. It would also cause loss of some sensation in the thumb and other
fingers, as well as weakness in both finger extension and of the biceps
reflex. Syringomyelia would produce bilateral segmental loss of pain and
temperature. A knife wound completely severing the nerve would result in
a functional loss similar to that experienced with an LMN paralysis. Polio
results in loss of LMNs, thus also producing an LMN paralysis. One of the
effects of AIDS is that it produces damage to the lateral and dorsal columns,
resulting in the appearance of a UMN disorder.
7-43. The answer is c. (Hardman, p 1401.) Propylthiouracil is more
strongly protein bound and crosses the placenta to a lesser degree than
methimazole and is, therefore, the safest antithyroid drug in pregnancy.
7-44. The answer is a. (Levinson, pp 130–131.) Brucella are small, aerobic, Gram-negative coccobacilli. Of the four well-characterized species of
Brucella, only one—B. melitensis—characteristically infects both goats and
humans. Brucellosis may be associated with gastrointestinal and neurologic
symptoms, lymphadenopathy, splenomegaly, hepatitis, and osteomyelitis.
7-45. The answer is d. (Cotran, pp 199–201.) A blood transfusion reaction
is a type II hypersensitivity reaction that is mediated by antibodies reacting
against antigens present on the surface of blood group antigens or irregular
antigens present on the donor’s red blood cells. Type II hypersensitivity reactions result from attachment of antibodies to changed cell surface antigens or
to normal cell surface antigens. Complement-mediated cytotoxicity occurs
when IgM or IgG binds to a cell surface antigen with complement activation
and consequent cell membrane damage or lysis. Blood transfusion reactions
and autoimmune hemolytic anemia are examples of this form. Systemic anaphylaxis is a type I hypersensitivity reaction in which mast cells or basophils
that are bound to IgE antibodies are reexposed to an allergen, which leads to
a release of vasoactive amines that causes edema and broncho- and vasoconstriction. Sudden death can occur. Systemic immune complex reactions are
found in type III reactions and are due to circulating antibodies that form
complexes upon reexposure to an antigen (such as foreign serum), which
then activates complement. This process is followed by chemotaxis and
aggregation of neutrophils, which leads to release of lysosomal enzymes and
eventual necrosis of tissue and cells. Serum sickness and Arthus reactions are
examples of type III reactions. Delayed type hypersensitivity is type IV and is
306
Clinical Vignettes for the USMLE Step 1
due to previously sensitized T lymphocytes, which release lymphokines
upon reexposure to the antigen. This takes time—perhaps up to several days
following exposure. The tuberculin reaction is the best-known example. T
cell–mediated cytotoxicity leads to lysis of cells by cytotoxic T cells in
response to tumor cells, allogenic tissue, and virus-infected cells. These cells
have CD8 antigens on their surfaces.
7-46. The answer is c. (Waxman, pp 66–67, 203.) A lesion of the spinal
canal that compresses the ventral commissure (syringomyelia) would interrupt ascending fibers crossing there but would not interfere with already
crossed fibers ascending in the lateral spinothalamic tracts. Pain and temperature sensation above and below the level of the cord lesion would be
preserved. The cell bodies of first-order afferent (sensory) neurons are
located in the dorsal root ganglia. Their central processes enter the spinal
cord and ascend one segment before synapsing with a second-order neuron
in the dorsal horn. The central processes of second-order neurons cross in
the ventral white commissure to the opposite side of the cord and ascend in
the lateral spinothalamic tract to the ventral posterior lateral nucleus of the
thalamus where they synapse with third-order neurons, which relay the
message to cortical neurons of the postcentral gyrus of the parietal lobe.
Lesions occurring unilaterally in a peripheral nerve would result in an ipsilateral deficit, whereas lesions in a crossed ascending pathway, in the thalamus, or in the cortex would result in contralateral deficits.
7-47. The answer is b. (McPhee, p. 140; Braunwald, pp 2460–2468.)
Numerous localized disorders and many systemic diseases can damage
the spinal cord or the peripheral nerves. The pattern of pain, sensory
loss, and sometimes weakness can help classify the disorder. A mononeuropathy involves pain/temperature and vibratory/joint position abnormalities, along the precise path of an individual nerve with associated
weakness and pain. Mononeuropathy multiplex involves multiple noncontiguous peripheral nerves in a sequential fashion taking place over
days to years. A radiculopathy involves a nerve root with dermatome distribution of both pain/temperature and vibratory/joint position abnormalities and weakness of the innervated muscles. Brown-Séquard’s
syndrome also involves pain/temperature and vibratory/joint position
abnormalities; however, the distribution is ipsilateral pain/temperature
and contralateral vibratory/joint position abnormalities with an ipsilat-
Block 7
Answers
307
eral motor deficit. A polyneuropathy similarly involves pain/temperature
and vibratory/joint position abnormalities with a stocking-glove distribution and painful paraesthesias.
7-48. The answer is c. (Chandrasoma, pp 799–806. Cotran, pp 361–364.)
Granuloma inguinale is a rare, sexually transmitted disease that is caused
by Calymmatobacterium donovani, a small, encapsulated gram-negative
bacillus. Infection results in a chronic disease that is characterized by
superficial ulcers of the genital region. Regional lymph node involvement
produces large nodular masses that develop extensive scarring. Specialized
culture medium is available, but its use is not practical. Serologic tests are
also not useful. Instead, histologic examination is used to demonstrate
Donovan bodies, which are organisms within the cytoplasm of macrophages. They are seen best with silver stains or Giemsa’s stain. Chancroid is
an acute venereal disease that is characterized by painful genital ulcers with
lymphadenopathy. It is caused by Haemophilus ducreyi, a small, gramnegative bacillus. Gram stains of the suppurative lesions or cultures on specialized media may be used to make the diagnosis. Serologic tests are not
useful. Neisseria gonorrheae, a gram-negative diplococcus, causes gonorrhea, an acute suppurative infection of the genital tract. In males it produces a purulent discharge (urethritis) and dysuria. In women, it may be
asymptomatic (50%), or it may produce infection of the cervix with accompanying vaginal discharge, dysuria, and abdominal pain. Ascending infections in women can lead to salpingitis, tuboovarian abscess, and pelvic
inflammatory disease (PID). Fitz-Hugh–Curtis syndrome refers to perihepatitis infection. In newborns, infection acquired during birth can produce a purulent conjunctivitis (ophthalmia neonatorum). This disease has
been prevented due to prophylactic therapy to newborn infants. A Gram
stain of the urethral or cervical exudate may reveal the intracytoplasmic
gram-negative diplococci, or the exudate can be cultured on special media.
Serologic tests are not useful. Characteristically, N. gonorrheae produces
acid from glucose, but not from maltose or lactose. The spirochete T. pallidum, the causative agent of syphilis, has not been grown on any culture
media; therefore, other means are available to aid in the diagnosis of
syphilis. Dark-field or immunofluorescence examination may be used to
detect organisms in the genital ulcers of primary syphilis. Antibodies to
cardiolipin, a substance in beef heart that is similar to a lipoid released by
T. pallidum, are used to screen for syphilis. This is the basis of both the
308
Clinical Vignettes for the USMLE Step 1
VDRL and the rapid plasma reagin (RPR) tests; however, these screening
tests are not totally specific. Chlamydia species are obligate intracellular
parasites that form elementary bodies and reticulate bodies. The former are
small, extracellular, and infectious, while the latter are intracellular and
noninfectious. Three Chlamydia species are C. psittaci, C. pneumoniae, and
C. trachomatis. The last causes several human diseases including trachoma,
inclusion conjunctivitis, nongonococcal urethritis, and lymphogranuloma
venereum (LGV). Specialized culture media and direct examination procedures are available to aid in the diagnosis of these diseases. The regional
lymph nodes in patients with lymphogranuloma venereum have a characteristic histologic appearance typified by necrotizing granulomas forming
stellate areas of necrosis. Trachoma is the leading cause of blindness in
underdeveloped countries. It is a chronic infection of the conjunctiva that
eventually scars the conjunctiva and cornea. Lymphogranuloma venereum
is a sexually transmitted disease that is characterized by the formation of a
genital ulcer with local necrotizing lymphadenitis. The skin test for LGV is
the Frei test, which consists of intradermal injection of LGV antigen. C.
psittaci is the causative agent of psittacosis (parrot fever). It produces a
severe pulmonary disease and should be suspected in patients with a history of bird contact, such as pet shop workers or parrot owners.
7-49. The answer is b. (Braunwald, pp 2016, 2023–2030, 2033–2034.)
The pattern and amount of radioiodine uptake on 123I scan is fundamental
to the correct diagnosis of thyrotoxicosis. Low-uptake thyrotoxicosis can
occur when there is destruction of the thyroid follicles with release of thyroid hormone, such as in subacute thyroiditis, which usually presents as
an exquisitely painful gland. Iodine-induced hyperthyroidism, factitious
hyperthyroidism, and painless (silent) thyroiditis also cause low-uptake
thyrotoxicosis.
7-50. The answer is a. (Afifi, pp 30–34; Nolte, pp 18–21.) Damage to a
nerve fiber proximal to its cell body will cause, among other changes, retrograde degeneration of the cell body. A number of changes occur in the
neuron during the process of retrograde degeneration. The cell body initially shows some swelling and becomes distended. At the beginning of the
degenerative process, there is an accumulation of mitochondria in the axoplasm at Ranvier’s nodes. The nucleus is then displaced toward the periph-
Block 7
Answers
309
ery of the cell. The Nissl granules break down, first in the center of the cell;
later, the breakdown spreads outward. In addition, the axonal process distal to the site of the lesion will undergo degeneration. It should be noted
that retrograde degeneration procedures were used experimentally prior to
the advent of histochemical methods for identifying cell bodies of origin of
given pathways in the CNS.
This page intentionally left blank.
BLOCK 8
Answers
8-1. The answer is a. (Hardman, p 1082. Katzung, pp 764–766.) The
third-generation cephalosporin, ceftriaxone, and cefixime are considered
first-line drugs in the treatment of gonorrhea because most strains of Neisseria gonococci are resistant to the penicillins. Amikacin and other aminoglycosides are used in serious infections caused by E. coli, Enterobacter,
Klebsiella, and Serratia species. However, spectinomycin, which is related
to the aminoglycosides, can be used as a backup drug for gonorrhea.
8-2. The answer is d. (Cotran, pp 864–867. Chandrasoma, pp 643–645.)
Several clinical syndromes may develop after exposure to any of the viruses
that cause hepatitis, including asymptomatic hepatitis, acute hepatitis, fulminant hepatitis, chronic hepatitis, and the carrier state. Asymptomatic
infection in individuals is documented by serologic abnormalities only. Liver
biopsies in patients with acute hepatitis, either the anicteric phase or the
icteric phase, reveal focal necrosis of hepatocytes (forming Councilman bodies) and lobular disarray resulting from ballooning degeneration of the hepatocytes. These changes are nonspecific, but the additional finding of fatty
change is suggestive of hepatitis C virus (HCV) infection. Clinically, acute
viral hepatitis is classified into three phases. During the prodrome phase,
patients may develop symptoms that include anorexia, nausea and vomiting, headaches, photophobia, and myalgia. An unusual symptom associated
with acute viral hepatitis is altered olfaction and taste, especially the loss of
taste for coffee and cigarettes. The next phase, the icteric phase, involves
jaundice produced by increased bilirubin. Patients may also develop light
stools and dark urine (due to disrupted bile flow) and ecchymoses (due to
decreased vitamin K). The final phase is the convalescence phase. Fulminant
hepatitis refers to massive necrosis and is seen in about 1% of patients with
either hepatitis B or C, but very rarely with hepatitis A infection. The biggest
risk for fulminant hepatitis is coinfection with both hepatitis B and D.
Chronic hepatitis is defined as elevated serum liver enzymes for longer than
6 months. Patients may be either symptomatic or asymptomatic.
311
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
312
Clinical Vignettes for the USMLE Step 1
8-3. The answer is b. (Moore & Dalley, pp 546, 561.) Perforating
branches of the deep femoral artery are the principal blood supply to the
posterior thigh. The other arteries supply anterior, medial, and gluteal
regions of the thigh.
8-4. The answer is d. (Simon, pp 138–145.) A neuritis involving the optic
disk would affect the size of the visual field loss around the optic disk,
which corresponds to the blind spot. In general, this kind of neuritis would
expand somewhat the size of the blind spot but would cause no further
visual loss.
8-5. The answer is a. (Ryan, pp 276–277.) The incidence of group B
streptococcal disease (GBS) is 1–3 cases per 1000 births. Neonates acquire
the disease during birth from mothers who harbor the organism. Risk factors include prematurity, premature rupture of membranes, and group B
streptococcal carriage. The Gram’s stain of cerebrospinal fluid is a rapid test
for GBS disease. Although sensitive, the Gram’s stain requires experience to
differentiate these streptococci from other Gram-positive cocci. Latex tests
for GBS antigen are also available, but sensitivity in CSF is not significantly
higher than the Gram’s stain. GBS can be reduced by intrapartum administration of penicillin. Experimentally, GBS polysaccharide vaccines have also
been used. Screening pregnant females early in pregnancy probably offers
little advantage because of the possible acquisition of GBS late in the pregnancy. There has been speculation concerning the pathogenesis of GBS.
These include failure to activate complement pathways and immobilization
of polymorphonuclear leukocytes (PMNs) due to the inactivation of complement C5A, a potent chemoattractant. While GBS is relatively more resistant
to penicillin than group A streptococci, the great majority of GBS isolates are
still penicillin-susceptible. An aminoglycoside such as gentamicin may be
added to GBS treatment regimens due to the relative reduced susceptibility
of some strains.
8-6. The answer is d. (Braunwald, pp 71, 1917–1918.) There is a high correlation between temporal arteritis and the occurrence of polymyalgia
rheumatica, and this would explain the proximal muscle girdle pain that is a
frequent finding in temporal arteritis. This disease is an inflammation of the
small arteries although there may be some involvement of the middle-sized
arteries. The only laboratory test to attempt to confirm your diagnosis is to
Block 8
Answers
313
obtain an ESR, which should be elevated above 100. Definitive diagnosis is
by temporal artery biopsy. Treatment with steroids prevents the occurrence
of blindness as a complication. The elevated level of alkaline phosphatase is
an incidental finding, perhaps because of alcohol consumption.
8-7. The answer is k. (Katzung, p 390.) Long-acting benzodiazepams
such as diazepam are useful in alcohol withdrawal. Its active metabolite is
eliminated slowly, thereby increasing its duration of action. In patients with
liver disease, short-acting agents might prove effective if they are metabolized to inactive water-soluble metabolites (e.g., oxazepam). Triazolam
would be useful because of its short duration of action.
8-8. The answer is a. (Moore & Dalley, p 673.) A mnemonic device for
remembering the order in which the soft tissues overlie the cranium is
SCALP: Skin, Connective tissue, Aponeurosis, Loose connective tissue, and
Periosteum. The scalp proper is composed of the outer three layers, of
which the connective tissue contains one of the richest cutaneous blood
supplies of the body. The occipitofrontal muscle complex inserts into the
epicranial aponeurosis, which forms the intermediate tendon of this digastric muscle. This structure, along with the underlying layer of loose connective tissue, accounts for the high degree of mobility of the scalp over the
pericranium. If the aponeurosis is lacerated transversely, traction from the
muscle bellies will cause considerable gaping of the wound. Secondary to
trauma or infection, blood or pus may accumulate subjacent to the epicranial aponeurosis.
8-9. The answer is b. (Murray, pp 627–661. Scriver, pp 2275–2296. Sack,
pp 121–138. Wilson, pp 287–320.) An elevation of pyruvate and a deficiency
of acetyl CoA suggest a deficiency of pyruvate dehydrogenase (PDH). This
multisubunit enzyme assembly contains pyruvate dehydrogenase, dihydrolipoyl transacetylase, dihydrolipoyl dehydrogenase, and two enzymes
involved in regulation of the overall enzymatic activity of the complex.
PDH requires thiamine pyrophosphate as a coenzyme, dihydrolipoyl
transacetylase requires lipoic acid and CoA, and dihydrolipoyl dehydrogenase has an FAD prosthetic group that is reoxidized by NAD+. Biotin, pyridoxine, and ascorbic acid are not coenzymes for PDH. An ATP-dependent
protein kinase can phosphorylate PDH to decrease activity, and a phosphatase can activate PDH. Increases of ATP, acetyl CoA, or NADH
314
Clinical Vignettes for the USMLE Step 1
(increased energy charge) and of fatty acid oxidation increase phosphorylation of PDH and decrease its activity. PDH is less active during starvation,
increasing pyruvate, decreasing glycolysis, and sparing carbohydrates. Free
fatty acids decrease PDH activity and would not be appropriate therapy for
PDH deficiency. PDH deficiency (246900, 312170) exhibits genetic heterogeneity, as would be expected from its multiple subunits, with autosomal and X-linked recessive forms. The infant also could be classified as
having Leigh’s disease (266150), a heterogenous group of disorders with
hypotonia and lactic acidemia that can include PDH deficiency.
8-10. The answer is d. (Gilroy, pp 612–628. Simon, pp 182–184.) GuillainBarré syndrome is an acute polyneuropathy whose occurrence frequently
follows a respiratory infection. It results in myalgia of the lower limbs, loss
of muscle tone and tendon reflexes, and some flaccidity. The disorder can
also affect the seventh cranial nerve. The disorder can produce diffuse
demyelination of the peripheral nerves with an increase in lymphocytes
present at the sites of demyelination. The other disorders listed are generally
progressive where eventual recovery without intervention is not known to
occur. Myasthenia gravis and lumbar disk prolapse would not show
demyelination and lymphocyte increases near the sites of demyelination.
Multiple sclerosis involves central nervous system (CNS) structures; therefore, the constellation of symptoms would be different. As indicated earlier,
MD is progressive with effects upon both proximal muscles and later in distal muscles.
8-11. The answer is c. (Hardman, pp 887, 889.) Bile acid-binding resins
bind more than just bile acids, and binding of simvastatin to cholestyramine is the most likely mechanism for decreased GI absorption.
Cholestyramine may also bind to several other drugs, including digoxin,
benzothiadiazides (thiazides), warfarin, vancomycin, thyroxine (T4), and
aspirin. Medications should be given one hour before or four hours after
cholestyramine.
8-12. The answer is d. (Kaplan, p 52.) An earlier study by Pauline Bart
argued that the role of full-time mother leaves women in a difficult and
depressed state when their children reach adulthood and leave home.
This was designated as the empty nest syndrome. Subsequent studies
have shown that this conventional wisdom is misleading; that women
Block 8
Answers
315
report less stress; that many newlyweds visit or telephone their parents,
use their cars, and so on; that with delayed marriage, getting children to
leave home is becoming a bigger problem; that middle-aged women who
had not launched their children reported much less positive self-concepts
than those who had, especially in interpersonal relationships; and that, in
general, women look forward to the freedom and opportunity acquired by
having their children launched. The increase in divorce at this age is more
often related to the departure’s unmasking of an empty marriage than to the
empty nest syndrome.
8-13. The answer is c. (Cotran, pp 284–286.) There are several mechanisms through which proto-oncogenes (p-oncs) can become oncogenic
(c-oncs). Normal cellular genes (proto-oncogenes) may become oncogenic
by being incorporated into the viral genome (forming v-oncs), or they may
be activated by other processes to form cellular oncogenes (c-oncs). These
other processes include gene mutations, chromosomal translocations, and
gene amplifications. Gene mutations, such as point mutations, are associated with the formation of cancers by mutant c-ras oncogenes. Chromosomal translocations are associated with the development of many types of
cancers, one example of which is Burkitt’s lymphoma. The most common
translocation associated with Burkitt’s lymphoma is t(8;14), in which the
c-myc oncogene on chromosome 8 is brought in contact with the immunoglobulin heavy chain gene on chromosome 14. Two other examples of chromosomal translocations are the association of chronic myelocytic leukemia
(CML) with t(9;22), which is the Philadelphia chromosome, and the association of follicular lymphoma with the translocation t(18;14). The former
involves the proto-oncogene c-abl, which is rearranged in proximity to a
break point cluster region (bcr) on chromosome 22. The resultant chimeric
c-abl/bcr gene encodes a protein with tyrosine kinase activity. The t(18;14)
translocation involves the bcl-2 oncogene on chromosome 18. Expression of
the oncogene bcl-2 is associated with the prevention of apoptosis in germinal centers. Examples of associations that involve gene amplification
include N-myc and neuroblastoma, c-neu and breast cancer, and erb-B and
breast and ovarian cancer. Gene amplifications can be demonstrated by
finding doublet minutes or homogenous staining regions.
8-14. The answer is c. (Hardman, p 890. Katzung, pp 588–589.) Only
niacin improves levels of VLDL, HDL, and LDL and inhibits cholesterol syn-
316
Clinical Vignettes for the USMLE Step 1
thesis. It also limits the progression of atherosclerosis by lowering circulating fibrinogen and increasing circulating tissue plasminogen activator (tPA).
8-15. The answer is b. (Katzung, p 411.) Severe hepatotoxicity of an
idiosyncratic nature is associated with valproic acid. The risk is very high
in the pediatric population, particularly in patients below the age of two.
Fatalities generally occur within four months of treatment. Hepatotoxicity
may be reversed in some individuals.
8-16. The answer is b. (Braunwald, p 1982.) The best screening test for
suspected acromegaly is an IGF-1. Random growth hormone varies too
much to be useful. IGF-1 is more consistent and does not fluctuate episodically throughout the day. TSH and prolactin may be abnormal but are not
diagnostic of acromegaly. Fasting blood sugar may be elevated in this
patient, but again it is not diagnostic.
8-17. The answer is e. (Baum, pp 230–234.) Sensory information alone
(what one can expect to feel) has been found to be the most effective type
of information. Coping information (e.g., teaching coping skills, ways to
relieve pain and discomfort) is the next most effective because it provides
the patient with some sense of control. Procedural information (what procedures will be done) makes the surgery more predictable, but does not
address the sensations one should expect. The most effective reduction of
stress is achieved by combining sensory and coping information so that the
patient is able to predict when pain will occur, how it will feel, and how to
cope with it. Studies confirm that it is important for the patient to be able
to establish or retain some sense of control.
8-18. The answer is a. (Katzung, p 1124.) Decreased gastrointestinal
absorption of ciprofloxacin occurs with antacids because of their ability to
adsorb the fluoroquinolone. Other preparations containing divalent ions,
such as iron, will impede fluoroquinolone absorption.
8-19. The answer is a. (Howard, pp 231–250.) Certain strains of staphylococci elaborate an enterotoxin that is frequently responsible for food poisoning. Typically, the toxin is produced when staphylococci grow on foods
rich in carbohydrates and is present in the food when it is consumed. The
resulting gastroenteritis is dependent only on the ingestion of toxin and not
on bacterial multiplication in the gastrointestinal tract. Characteristic
Block 8
Answers
317
symptoms are nausea, vomiting, abdominal cramps, and explosive diarrhea. The illness rarely lasts more than 24 h.
8-20. The answer is d. ( Young, p 358. Junqueira, pp 440–441. Yen, pp
714–715.) The patient described in this question is probably pregnant. The
delay in menstruation coupled with the presence of basophilic cells in a
vaginal smear are clues. Ovulation is the midpoint of the cycle and should
be more than a few days away. She is relatively young for the onset of
menopause and there are no other symptoms. The vaginal epithelium
varies little with the normal menstrual cycle. Exfoliative cytology can be
used to diagnose cancer and to determine if the epithelium is under stimulation of estrogen and progesterone. The presence of basophilic cells in the
smear with the Pap-staining method would indicate the presence of both
estrogen and progesterone. The data suggest the maintenance of the corpus
luteum (i.e., pregnancy).
8-21. The answer is e. (Murray, pp 412–434. Scriver, pp 3–45. Sack, pp
3–29. Wilson, pp 99–121.) The process of transduction involves the transfer
of a portion of DNA from one bacterium to the chromosome of another
bacterium by means of a viral infection. Conjugation is the transfer of a socalled male chromosomal DNA to the DNA of an acceptor, or female, bacterial cell. Colinearity defines the relationship between genes and proteins
in that the sequence of amino acids in proteins is a result of the sequence
of base triplets in template genes. Recombination is simply the exchange of
sequences between two molecules of DNA. Transformation results when
exogenous DNA fragments are incorporated into the chromosome of
another organism, as in the transformation of pneumococcal bacteria that
led Avery and McLeod to recognize the genetic significance of DNA.
8-22. The answer is c. (Gilroy, pp 199–211.) Multiple sclerosis is a
demyelinating autoimmune disease that affects CNS function. This disorder produces a wide variety of symptoms, including sudden sensory dysfunction and loss, which affect vision and the somatosensory system,
causing tingling, pain, and hypesthesia. Broad functional motor disturbances also occur, including weakness of the upper or lower limbs, UMN
signs, and gait impairment. There is also bladder dysfunction as well as an
increase in CSF protein and IgG synthesis. Diffuse cerebellar degeneration
would produce gait ataxia and deficits in the accuracy of intentional movements. ALS would produce both a UMN and an LMN paralysis, which typ-
318
Clinical Vignettes for the USMLE Step 1
ically does not extend to sensory functions. Likewise, a peripheral neuropathy would not produce UMN signs, visual deficits, and extensive
motor disturbances as described in this case. A tumor of the prefrontal cortex would affect some cognitive and emotional functions, but it would not
affect sensory processes such as vision and somatosensation, nor would it
produce signs of a UMN disorder or muscle weakness.
8-23. The answer is a. (Hughes, pp 109–110.) Many people avoid taking
action in an emergency situation. The farther away the bystander is and the
more people present, the less likely is a bystander to get involved. One is
more apt to help the more one knows what to do, the fewer people present,
if one is a male, if the victim does not appear to be responsible for his or
her mishap (e.g., stroke victim versus drunk), if the negative consequences
to the bystander are minimal and the positive consequences reasonable, if
the bystander’s freedom is not limited by helping, if the bystander is somehow forced to get involved, if someone else is acting as a helping model,
and if the victim is dependent or without resources or has helped the
bystander in the past. Altruism is most easily learned through positive reinforcement and imitation.
8-24. The answer is c. (Braunwald, p 160.) This is the typical Argyll
Robertson pupil found in syphilis. The RPR (rapid plasma reagin), a nontreponemal antibody test for syphilis, will be positive.
8-25. The answer is e. (Katzung, p 116). High concentrations of atropine
block all parasympathetic function. The patient usually presents with an
array of symptoms and signs that include dry mouth, dilated pupils, tachycardia, red and hot skin, and delirium. Hyperthermia may occur, particularly in very young children.
8-26. The answer is d. (Murray, pp 452–467. Scriver, pp 3–45. Sack, pp
1–40. Wilson, pp 101–120.) The deadly mushroom A. phalloides has several
toxins. A major toxin is α-amanitin, an octapeptide that inhibits mRNA
synthesis by very tightly binding RNA polymerase II (DNA-dependent
RNA polymerase). As little as one of the mushrooms (know as the deathcap, death-cup, or avenging angel) delivers a lethal dose of about 10 mg
α-amanitin. Severe, irreversible liver damage occurs quickly, leading to
death. At higher concentrations, the toxin can inhibit RNA polymerase III
and tRNA synthesis. Polymerase I is unaffected. Since α-amanitin is effec-
Block 8
Answers
319
tive at concentrations of 10−9 to 10−8 M, it has been useful as a research tool
for studying RNA polymerase function.
8-27. The answer is d. (Cotran, pp 387–388, 807–809.) Yersinia (formerly
called Pasteurella) is an important genus of gram-negative bacilli that
causes a wide variety of human and animal disease, ranging from plague (Y.
pestis) to acute mesenteric lymphadenitis (Y. enterocolitica) in older children
and young adults. Y. enterocolitica infections also occur in the terminal
ileum in young adults, causing an ileitis that produces inflammation not
unlike that seen in some stages of Crohn’s disease (regional enteritis). Since
the organisms grow slowly on enrichment media, they may be overgrown
by other coliforms at 37°C. The organisms may be isolated by means of
cold enhancement at 4°C.
8-28. The answer is c. (Hardman, p 408.) Clozapine differs from other
neuroleptic agents in that it can induce seizures in nonepileptic patients. In
patients with a history of epileptic seizures for which they are not receiving
treatment, stimulation of seizures can occur following the administration of
neuroleptic agents because they lower seizure threshold and cause brain
discharge patterns reminiscent of epileptic seizure disorders.
8-29. The answer is d. (Murray, pp 452–467. Scriver, pp 3–45. Sack, pp
1–40. Wilson, pp 101–120.) The gene that produces the deadly toxin of
Corynebacterium diphtheriae comes from a lysogenic phage that grows in the
bacteria. Prior to immunization, diphtheria was the primary cause of death
in children. The protein toxin produced by this bacterium inhibits protein
synthesis by inactivating elongation factor 2 (EF-2, or translocase). Diphtheria toxin is a single protein composed of two portions (A and B). The B
portion enables the A portion to translocate across a cell membrane into
the cytoplasm. The A portion catalyzes the transfer of the adenosine
diphosphate ribose unit of NAD1 to a nitrogen atom of the diphthamide
ring of EF-2, thereby blocking translocation. Diphthamide is an unusual
amino acid residue of EF-2.
8-30 through 8-32. The answers are 8-30 d, 8-31 c, 8-32 b. (Gilroy,
pp 587–589. Afifi, pp 163–165.) Taste associated with the anterior two-thirds
of the tongue is mediated by the facial (cranial nerve VII) nerve. The geniculate ganglion contains the cell bodies associated with the sensory (gustatory)
component of the seventh nerve. The somatic motor component of the sev-
320
Clinical Vignettes for the USMLE Step 1
enth nerve mediates the muscles of facial expression. Thus, the sensory and
motor components of the seventh nerve affected in this individual can be
characterized as special visceral afferent (because this afferent contains
chemoreceptors) and special visceral efferent (because the motor component
innervates skeletal muscle and is derived from a branchial arch), respectively.
8-33. The answer is b. (Moore & Dalley, pp 541–542.) The saphenous
nerve accompanies the great saphenous vein along the medial aspect of the
leg and foot as far as the great toe. The superficial fibular nerve innervates
the central portion of the dorsum of the foot. The sural cutaneous nerve
innervates the lateral aspect of the foot. The medial and lateral plantar
branches of the tibial nerve supply the sole of the foot.
8-34. The answer is b. (Murray, pp 412–434. Scriver, pp 3–45. Sack, pp
3–29. Wilson, pp 99–121.) The Ames test is a rapid and relatively inexpensive bacterial assay for determining mutagenicity of potential toxic chemicals. Since many chemical carcinogens are mutagenic, it seems obvious that
damage to DNA is a central event in carcinogenesis as well as mutagenesis.
Dr. Bruce Ames developed a tester strain of Salmonella that has been modified not to grow in the absence of histidine because of a mutation in one of
the genes for the biosynthesis of histidine. Toxic chemicals that are mutagens are placed in the center of the plate and result in reversions of the
original mutations, so that histidine is synthesized and the mutated revertants multiply in histidine-free media. Since many carcinogens are converted to active forms by metabolism in the liver, preliminary incubation
with liver homogenates may precede the bacterial assay. Essentially all
chemicals known as carcinogens in humans cause mutagenesis in the Ames
test. The other options—carcinogenicity screening in immunosuppressed
(nude) mice, computer modeling, or incubation with mammalian cell cultures—may provide some information, but are less efficient and validated
than the Ames test. Contamination of Michigan cattle feed with polychlorinated biphenyls (PCBs) did occur through an industrial mistake.
8-35. The answer is c. (Braunwald, pp 2469–2472.) This woman likely
has myasthenia gravis; the incidence in women peaks in their twenties and
thirties and women are more often affected, about 3:2, than men. Measurement of the antibody antiacetylcholine receptor provides a definitive
diagnosis in 90% of cases of generalized disease, which this patient manifests, and 50% in ocular disease alone. Single-fiber electromyography is not
Block 8
Answers
321
specific for myasthenia gravis. Edrophonium chloride test, if unequivocally
positive, makes the diagnosis highly probable. CT scan, MRI scan, and the
EEG do not play a role in the diagnosis of myasthenia gravis.
8-36. The answer is a. (Hardman, p 338. Katzung, pp 438–439.) Ester-type
local anesthetics are mainly hydrolyzed by pseudocholinesterases. Amidetype local anesthetics are hydrolyzed by microsomal enzymes in the liver. Of
the listed agents, only lidocaine is an amide and can be influenced by liver
dysfunction.
8-37. The answer is d. (Ryan, pp 550–555.) A male patient with the presentation as outlined (fatigue, weight loss, and lymphadenopathy) must be
tested for antibodies to HIV. While other antibody tests may be relevant after
the primary diagnosis, they must be considered after HIV is ruled out. Certainly, infectious mononucleosis is a possibility, but its occurrence in this age
group is not as frequent as HIV. Patients are tested first by an ELISA screening test. If this test is positive (X2), then a confirmatory Western blot is performed. A Western blot separates the immune response into antibody
production for specific components of the virus, that is, envelope, gag, and
so forth. The following table shows the various bands that could be seen on
a widely used Western blot and their identification by specific antigen
source. There are at least three schemes for interpreting Western blots.
Assuming technical competence in the laboratory, one of the more common
reasons for falsely positive ELISAs and Western blots is an influenza vaccination within the past few months. A rare patient may have antibody to the cell
line used to grow virus. Unlike Lyme disease, there is no reported crossreactivity with Epstein-Barr virus (EBV) or HTLV. There appears to be no naturally occurring antibody to retroviruses.
Antigen
Source
gp 160
gp 120
gp 41
gp 31
gp 51
p 66
p 24
env gene product
env fragment
transmembrane fragment
pol gene product
core protein (gag)
Abbreviations: gp, glycoprotein; p, protein; env, envelope; pol, polymerase.
322
Clinical Vignettes for the USMLE Step 1
8-38. The answer is d. (Cotran, pp 1275–1276.) Inflammatory polyneuropathies may be acute or chronic. Acute inflammatory demyelinating
polyradiculoneuropathy (Guillain-Barré syndrome) is a life-threatening
disease of the peripheral nervous system. The disease usually follows
recovery from an influenza-like upper respiratory tract infection and is
characterized by a motor neuropathy that leads to an ascending paralysis
that begins with weakness in the distal extremities and rapidly involves
proximal muscles. Sensory changes are usually minimal. The disease is
thought to result from immune-mediated segmental demyelination. In rare
patients, instead of an acute course, Guillain-Barré syndrome takes a
chronic course with remissions and relapses. This process is called chronic
inflammatory demyelinating polyradiculoneuropathy (CIDP).
8-39. The answer is d. ( Junqueira, pp 385–386, 393, 395. Moore, Developing Human, p 320.) The newborn described is genotypically female and suffers from adrenogenital or congenital virilizing hyperplasia in which there is
a deficiency in the pathway that leads to cortisol synthesis. The inability to
synthesize cortisol in turn leads to production of high levels of ACTH and
ACTH-releasing factor from the hypothalamus. The result is hypertrophy of
the fetal adrenal cortex, which is a critical fetal structure that produces
dehydroepiandrosterone. The excessive production of androgens by the
fetal adrenal leads to masculinization of the female genitalia. Increased
secretion of cortisol cannot occur because of the metabolic defect in this
pathway; therefore, negative feedback control is not functional. The fetal
cortex is part of maternal-feto-placental unit because the dehydroepiandrosterone is used by the placenta to produce estradiol. The fetal adrenal
cortex involutes following birth, causing an overall reduction in the size of
the adrenal. The adult cortex (zona glomerulosa, zona fasciculata, and zona
reticularis) replaces the fetal adrenal cortex. The zona fasciculata and zona
reticularis produce androgens after birth. Vasopressin [AVP; also known as
antidiuretic hormone (ADH)] is released by the posterior pituitary and regulates fluid balance. ADH increases the permeability of the collecting duct
through an aquaporin-mediated mechanism. Androgen insensitivity is the
cause of testicular feminization and is not a factor in the adrenogenital syndrome.
8-40. The answer is e. (Conger, pp 337–339.) The nature of an adolescent
boy’s relationship with his parents is the single factor most predictive of
Block 8
Answers
323
juvenile delinquency. In the most extensive study of the subject, J. G. Bachman found that the better a boy reported he got along with his parents, the
less likely he was to engage in delinquent behavior. Other studies have
found that delinquency is related to overly severe punishment and overly
lax home disciplines as well as to an atmosphere of mutual hostility and
rejection between parents and children. Despite the widely held belief that
most delinquents come from broken homes, recent evidence indicates that
the incidence of delinquency among boys of unhappy, though intact,
homes is greater than that among boys of broken homes.
Gerald Patterson has identified four “lacks” in the family interactions
of delinquents: lack of house rules, lack of parental monitoring of behavior,
lack of effective contingencies resulting in inconsistent responses to unacceptable behavior, and lack of effective ways of dealing with family crises
that lead to tension and unresolved disputes.
8-41. The answer is a. (Braunwald, p 1982.) Transsphenoidal surgery
has the advantages of potential cure with rapid therapeutic response. If the
tumor is completely resected, the patient may experience a complete cure.
Medical therapy with somatostatin agonist or bromocriptine is helpful, but
the patient is dependent on medical therapy indefinitely. Irradiation takes
years for full effectiveness and the patient may develop hypopituitarism.
Transfrontal surgery is rarely used now.
8-42. The answer is b. (Katzung, pp 727–728.) Metformin is contraindicated in patients with type II diabetes in a number of instances, including
renal disease, liver disease, chronic cardiopulmonary dysfunction leading
to hypoxia, and alcoholism.
8-43. The answer is d. (Simon, pp 138–145.) From the lateral geniculate
nucleus, there are two trajectories that the fiber pathways take en route to
the visual cortex. One pathway passes dorsally through the parietal lobe
and terminates in the upper bank of the calcarine fissure in the ipsilateral
primary visual cortex. The second pathway takes a more circuitous (ventral) route—called the Meyer-Archambault loop—through the temporal lobe
and terminates in the lower bank of the calcarine fissure in the ipsilateral
primary visual cortex. The lower bank of the calcarine fissure is associated
with the upper visual quadrants of the contralateral visual fields for both
eyes, while the upper bank of the calcarine fissure is associated with the
324
Clinical Vignettes for the USMLE Step 1
lower quadrants of the contralateral visual fields for both eyes. Thus, if
there is a lesion of the left temporal lobe affecting the Meyer-Archambault
loop, then the right upper quadrant for each eye will be affected. This
deficit is referred to as a right upper quadrantanopia.
8-44. The answer is d. (Hardman, pp 4–9. Katzung, pp 41–43.) Bioavailability is defined as the fraction or percentage of a drug that becomes
available to the systemic circulation following administration by any
route. This takes into consideration that not all of an orally administered
drug is absorbed and that a drug can be removed from the plasma and
biotransformed by the liver during its initial passage through the portal
circulation. A bioavailability of 25% indicates that only 20 mg of the
80-mg dose (i.e., 80 mg × 0.25 = 20 mg) reached the systemic circulation. Organ clearance can be determined by knowing the blood flow
through the organ (Q) and the extraction ratio (ER) for the drug by the
organ, according to the equation
CLorgan = Q × ER
The extraction ratio is dependent upon the amounts of drug entering (Ci)
and exiting (Co) the organ:
Ci × Co
ER = ᎏ
Ci
In this problem, the amount of verapamil entering the liver was 76 mg
(80 mg × 0.95) and the amount leaving was 20 mg. Therefore,
76 mg − 20 mg
ER = ᎏᎏ = 0.74
76 mg
CLliver = (1500 mL/min) (0.74) = 1110 mL/min
8-45. The answer is e. (Ryan, pp 282–283.) Enterococci causes a wide
variety of infections ranging from less serious, for example, urinary tract
infections, to very serious, such as septicemia. A Gram-positive coccus resistant to penicillin must be assumed to be enterococcus until other more
definitive biochemical testing places the isolate in one of the more esoteric
groups of Gram-positive cocci. Once isolated, there are a variety of tests
to speciate enterococci. However, penicillin-resistant, non-β-lactamase-
Block 8
Answers
325
producing, vancomycin-resistant, Gram-positive cocci are most likely Enterococcus faecium. There are a variety of mechanisms for vancomycin resistance in E. faecium and they have been termed Van A, B, or C. These isolates
have become one of the most feared nosocomial pathogens in the hospital
environment. Unfortunately, no approved antibiotics can successfully treat
vancomycin-resistant enterococci (VRE), only some experimental antibiotics such as Synercid.
8-46. The answer is b. (Afifi, pp 513–521.) The symptoms described are
characteristic of hydrocephalus. Hydrocephalus may come about as a result
of defects such as the failure of formation of the cerebellar vermis, foramens
of Magendie and Luschka, or of the corpus callosum. There is an enlarged
cranium as a result of the buildup of cerebrospinal fluid (CSF), causing
brain damage. Several of the symptoms may also be caused by a compression of the posterior fossa and the absence of a cerebellar vermis. Cleft
palate is a fissure of the medial aspect of the lip and would not result in the
symptoms described previously. Anencephaly is the complete or partial
absence of the brain and is not compatible with life. Syringomyelia is associated with bilateral segmental loss of pain and temperature. A congenital
aneurysm can occur in a variety of places within the CNS and is typically
associated with stroke in the adult.
8-47. The answer is d. (Cotran, pp 869, 875–876. Chandrasoma, pp
655–658.) Reye’s syndrome (RS) is an acute postviral illness that is seen
mainly in children. It is characterized by encephalopathy, microvesicular
fatty change of the liver, and widespread mitochondrial injury. Electron
microscopy (EM) reveals large budding or branching mitochondria. The
mitochondrial injury results in decreased activity of the citric acid cycle
and urea cycle and defective β-oxidation of fats, which then leads to the
accumulation of serum fatty acids. The typical patient presents several
days after a viral illness with pernicious vomiting. RS is associated with
hyperammonemia, elevated serum free fatty acids, and salicylate (aspirin)
ingestion.
In contrast, Wilson’s disease, which is related to excess copper deposition within the liver and basal ganglia of the brain, is characterized by varying liver disease and neurologic symptoms. The liver changes vary from
fatty change to jaundice to cirrhosis, while the neurologic symptoms consist of a Parkinson-like movement disorder and behavioral abnormalities. A
326
Clinical Vignettes for the USMLE Step 1
liver biopsy may reveal steatosis, Mallory bodies, necrotic hepatocytes, or
cholestasis. Increased copper can be demonstrated histologically using
the rhodamine stain. α1 antitrypsin deficiency causes both liver disease
and lung disease, especially panacinar emphysema. Liver biopsies reveal
red blobs within the cytoplasm of hepatocytes that are PAS-positive and
diastase-resistant. Dubin-Johnson syndrome is associated with conjugated
hyperbilirubinemia that results from decreased hepatic excretion of conjugates of bilirubin.
8-48. The answer is b. (Rhoades, p 38.) Periodic hyperkalemic paralysis
is caused by inactivation of the skeletal muscle membranes. Inactivation is
produced by depolarization of the skeletal muscle membrane, which
occurs when extracellular potassium concentration increases. Inactivation
of the sodium channels on the skeletal muscle membrane prevents action
potentials from being produced and therefore leads to muscle weakness or
paralysis. Although the exact mechanism of periodic hyperkalemic paralysis is not known, it appears to be due to a mutation in the gene coding for
the sodium inactivation gate.
8-49. The answer is a. (Nolte, pp 485–492.) The classic appearance of a
patient with a lesion of the cerebellar hemispheres is one in which voluntary and skilled movements are affected. They are uncoordinated and there
are errors in the range, force, and direction of movement. The relationships
between the cerebellum and the motor regions of the cerebral cortex have
been disrupted. Lesions of other regions such as the flocculonodular lobe,
vermal region of the anterior cerebellar cortex, or fastigial nucleus produce
different symptoms (disturbances of balance, muscle tone, or nystagmus).
Although pure lesions limited to the ventral spinocerebellar tract have not
been reported, it is likely that such a lesion could not account for the symptoms indicated in this question. Information carried by this tract concerns
activity of Golgi tendon organs of muscles of the lower limbs.
8-50. The answer is c. (Damjanov, pp 886–887, 928–930. Duchin, pp
949–955.) The Hantavirus genus belongs to the Bunyaviridae family and
includes the causative agent of a group of diseases that occur throughout
Europe and Asia and are referred to as hemorrhagic fever with renal syndrome. The characteristic features of this syndrome are hematologic abnormalities, renal involvement, and increased vascular permeability.
Block 8
Answers
327
Respiratory involvement is generally minimal in these diseases. Although
several species of rodents in the United States are known to be infected
with Hantavirus, no human cases were reported until an outbreak of severe,
often fatal respiratory illness occurred in the United States in May 1993 in
the Four Corners area of New Mexico, Arizona, Colorado, and Utah. This
illness resulted from a new member of the genus Hantavirus that caused a
severe disease characterized by a prodromal fever, myalgia, pulmonary
edema, and hypotension. The main distinguishing feature of this illness,
which is called Hantavirus pulmonary syndrome, is noncardiogenic pulmonary edema resulting from increased permeability of the pulmonary
capillaries. Laboratory features common to both Hantavirus pulmonary
syndrome and hemorrhagic fever with renal syndrome include leukocytosis, atypical lymphocytes, thrombocytopenia, coagulopathy, and decreased
serum protein concentrations. Abdominal pain, which can mimic an acute
abdomen, may be found in both Hantavirus pulmonary syndrome and
hemorrhagic fever with renal syndrome.
Dengue fever virus is a type of flavivirus; flaviviruses which are similar
to alphaviruses. Dengue fever (breakbone fever) is initially similar to
influenza but then progresses to a rash, muscle pain, joint pain, and bone
pain. It can produce a potentially fatal hemorrhagic disorder. Yellow fever
virus, which causes yellow fever, is another flavivirus. It is spread by a mosquito and produces characteristic coagulative necrosis of liver acinar zone
2 (midzonal necrosis). The necrotic hepatocytes produced by the process
of apoptosis in the absence of inflammation result in Councilman bodies.
Because of liver failure, patients become jaundiced (hence the term yellow
fever) and may vomit clotted blood (“black vomit”). Another flavivirus is
the cause of St. Louis encephalitis, which is spread by the Culex mosquito.
Alphaviruses, a type of togavirus, are similar to flaviviruses. They are the
prototypical arboviruses, which are arthropod-born viruses. Clinical diseases include eastern equine encephalitis (EEE), western equine encephalitis (WEE), and Venezuelan equine encephalitis (VEE). Ebola virus is a
member of the Filoviridae family that causes a severe hemorrhagic fever.
Outbreaks occur in Africa and typically make the national news.
This page intentionally left blank.
Bibliography
Adams RD, Victor M, Ropper AH: Principles of Neurology, 6/e. New York,
McGraw-Hill, 1997
Afifi AK, Bergman RA: Functional Neuroanatomy. New York, McGraw-Hill,
1998.
Alberts B, et al: Molecular Biology of the Cell, 3/e. New York, Garland, 1994.
April EW: Clinical Anatomy. 3/e. New York, John Wiley & Sons, 1997.
Ash LR, Orihel TC: Atlas of Human Parasitology, 4/e, Chicago, ASCP, 1997.
Baum A, Gatchel RJ, Krantz DS: An Introduction to Health Psychology, 3/e.
New York, McGraw-Hill, 1997.
Berne RM, Levy MN: Principles of Physiology, 3/e. St. Louis, Mosby, 2000.
Braunwald E, Fauci AS, Kasper DL, Hauser SL, Longo DL, Jameson JL (eds):
Harrison’s Principles of Internal Medicine, 15/e. New York, McGraw-Hill,
2001.
Brust JCM: The Practice of Neuroscience. New York, McGraw-Hill, 2000.
Carlson NR: Physiology of Behavior, 5/e. Boston, Allyn & Bacon, 1994.
Carpenter MB: Core Text of Neuroanatomy, 4/e. Baltimore, Williams &
Wilkins, 1991.
Champe PA, Harvey RA: Biochemistry, 2/e. Philadelphia, Lippincott, 1994.
Chandrasoma P, Taylor CR: Concise Pathology, 3/e. Stamford, CT, Appleton
& Lange, 1998.
Coe FL, Favus MJ (eds): Disorders of Bone and Mineral Metabolism. New York,
Raven, 1992.
Conger JJ: Adolescence and Youth: Psychological Development in a Changing World, 5/e. New York, Addison-Wesley Educational Publishers,
1997.
Connolly HM, Crary JL, et al: Valvular heart disease associated with
fenfluramine-phentermine. N Engl J Med 337(9):581–588, 1997.
Cotran RS, Kumar V, Robbins SL: Pathologic Basis of Disease, 6/e. Philadelphia,
Saunders, 1999.
Damjanov I, Linder J (eds): Anderson’s Pathology, 10/e. St. Louis, Mosby, 1996.
Duchin JS, et al: Hantavirus pulmonary syndrome: A clinical description of
17 patients with a newly recognized disease. N Engl J Med 330:949–955,
1994.
Ebert MH, Loosen PT, Nurcombe B: Current Diagnosis and Treatment in Psychiatry. New York, McGraw-Hill, 2000.
Gilroy, J: Basic Neurology, 3/e. New York, McGraw-Hill, 2000.
329
Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
330
Bibliography
Greenspan FS, Gardner DG: Basic & Clinical Endocrinology, 6/e. New York,
McGraw-Hill, 2001.
Guyton AC, Hall JE: Textbook of Medical Physiology, 10/e. Philadelphia,
Saunders, 2000.
Hardman JG, Limbird LE (eds): Goodman & Gilman’s the Pharmacological
Basis of Therapeutics, 9/e. New York, McGraw-Hill, 1996.
Hazzard WR, et al (eds): Principles of Geriatric Medicine and Gerontology, 4/e.
New York, McGraw-Hill, 1999.
Henry JB, et al (eds): Clinical Diagnosis and Management by Laboratory Methods, 19/e. Philadelphia, Saunders, 1996.
Howard BJ, Keiser JF, Smith TF, Weissfeld AS, Tilton RC: Clinical and Pathogenic Microbiology, 2/e, St. Louis, Mosby, 1993.
Hughes M, Kroehler CJ, Vander Zanden JW: Sociology: The Core, 5/e. New
York, McGraw-Hill, 1999.
Junqueira LC, Carneiro J, Kelley RO: Basic Histology, 9/e. Stamford, CT,
Appleton & Lange, 1998.
Kandel ER, Schwartz JH, Jessel TM: Principles of Neural Science, 4/e. New
York, McGraw-Hill, 2000.
Kaplan HL, Sadock BJ: Synopsis of Psychiatry, 8/e. Baltimore, Williams &
Wilkins, 1998.
Katzung BG: Basic and Clinical Pharmacology, 8/e. New York, McGraw-Hill,
2001.
Kingsley RE: Concise Text of Neuroscience, 2/e. Philadelphia, Lippincott,
Williams & Wilkins, 2000.
Kumar, V, Cotran RS, Robbins SL. Basic Pathology, 6/e. Philadelphia, Saunders, 1997.
Levinson W, Jawetz E: Medical Microbiology & Immunology, 6/e, New York,
McGraw-Hill, 2000.
Martin JH: Neuroanatomy, 2/e, Stamford, CT, Appleton & Lange, 1996.
McKenzie, JC, Klein RM: Basic Concepts in Cell Biology and Histology. New
York, McGraw-Hill, 2000.
McPhee SJ, Lingappa VR, Ganong WF, Lange JD (eds): Pathophysiology of
Disease, 2/e. Stamford, Connecticut, Appleton & Lange, 1997.
Moore KL, Persaud TVN: Before We Are Born, 5/e. Philadelphia, Saunders,
1998.
Moore KL, Persaud TVN: The Developing Human, 6/e. Philadelphia, Saunders, 1998.
Bibliography
331
Moore KL, Dalley AF: Clinically Oriented Anatomy, 4/e. Baltimore, Lippincott, Williams & Wilkins, 1999.
Murray RK, Granner DK, Mayes PA, Rodwell, VW: Harper’s Biochemistry,
25/e. New York, McGraw-Hill, 2000.
Murray PR, Rosenthal KS, Kobayashi GS, Pfaller MA: Medical Microbiology,
5/e. St. Louis, Mosby, 1997.
Noback CR, Strominger NL, and Demarest RJ: The Human Nervous System,
4/e. Philadelphia, Lea & Febiger, 1991.
Nolte J: The Human Brain: An Introduction to Its Functional Anatomy, 4/e. St.
Louis, MO, Mosby, 1999.
Plomin R, DeFries JJ, McClearn GE, Rutter M: Behavioral Genetics: A Primer,
3/e. New York, WH Freeman, 1997.
Purves D, Augustine GJ, Fitzpatrick D, Katz LC, LaMantia A-S, McNamara
JO, Williams SM: Neuroscience, 2/e. Sunderland, Sinauer Associates,
Inc., 2001.
Raoult D, Tilton RC: Dictionary of Infectious Diseases, Elsevier, New York,
2000.
Rhoades RA, Tanner GA: Medical Physiology. Boston, Little, Brown and
Company, 1995.
Rubin E, Farber JL: Pathology, 3/e. Philadelphia, Lippincott, 1999.
Ryan KT (ed): Sherris’s Medical Microbiology, 3/e, Appleton & Lange, Stamford, CT, 1994.
Sack GH Jr: Medical Genetics. New York, McGraw-Hill, 1999.
Scriver CR, Beaudet AL, Sly WS, Valle D: The Metabolic and Molecular Bases
of Inherited Disease, 7/e. New York, McGraw-Hill, 1995.
Siegel GJ, Agranoff BW, Albers RW, Fisher SK, Uhler MD: Basic Neurochemistry, 6/e. Philadelphia, Lippincott, Williams & Wilkins, 1999.
Sierles FS (ed): Behavioral Science for Medical Students, Baltimore, Williams
& Wilkins, 1993.
Simon RP, Aminoff MJ, Greenberg DA: Clinical Neurology, 4/e. New York,
McGraw-Hill, 1999.
Sweeney L: Basic Concepts in Embryology: A Student’s Survival Guide. New
York, McGraw-Hill, 1998.
Taylor SE: Health Psychology, New York, McGraw-Hill, 1995.
Waxman SG: Correlative Neuroanatomy, 24/e. New York, McGraw-Hill, 2000.
Wedding D: Behavior and Medicine, 2/e. St. Louis, Mosby-Year Book, 1995.
Wilson GN: Clinical Genetics: A Short Course. New York, Wiley-Liss, 2000.
332
Bibliography
Yen SSC, Jaffe RB, Barbieri RL: Reproductive Endocrinology, 4/e. Philadelphia,
Saunders, 1991.
Young B, Heath JW: Wheater’s Functional Histology, 4/e. New York, Churchill
Livingstone, 2000.
Many genetic diseases cited in this book include a six-digit McKusick number that allows reference to the compendium of genetic diseases that is
available in hard copy or online. This compendium is now maintained by
the National Institutes of Health and lists more than 4000 genetic diseases and genetic loci. For all but the most recently entered disorders, the
McKusick number provides the inheritance mechanism. Those numbers
beginning with 1 designate autosomal dominant diseases, those beginning
with 2 autosomal recessive diseases, those beginning with 3 X-linked recessive diseases, those beginning with 4 Y-linked diseases (so far only gene
loci), and those beginning with 5 mitochondrial DNA–encoded diseases.
NOTES
NOTES
NOTES
NOTES
NOTES
NOTES
NOTES
NOTES
NOTES
NOTES