Chapter 1
General Concepts of Disease:
Principles of Diagnosis
Learning Objectives
• Define:
– Disease
– Lesions
– Organic and functional disease
– Symptomatic and asymptomatic disease
– Etiology
– Pathogenesis
• Categories of human disease
• Types of diagnostic tests and procedures
Characteristics of Disease (1 of 3)
• Disease: disturbance of body structure or
function
• Lesions: well-defined, characteristic structural
changes in organs and tissues as a result of
disease
• Organic disease
– Associated with structural changes
– Gross examination
– Histologic examination
• Functional disease
– No morphological abnormalities yet body functions
are profoundly disturbed
Characteristics of Disease (2 of 3)
• Pathology: study of disease
– Pathologist: physician who specializes in diagnosing
and classifying diseases by studying the morphology
of cells and tissues
– Clinician: physician/health care professional that
cares for patients
• Symptoms: subjective manifestations such as
pain or weakness
• Signs: physical findings or objective
manifestations such as swelling or redness
Characteristics of Disease (3 of 3)
• Symptomatic disease: with symptoms and/or signs
• Asymptomatic disease: no signs or symptoms
– Distinction between asymptomatic and symptomatic
depends on extent
– Early stages of disease, usually asymptomatic
– If not treated, progresses to symptomatic
• Etiology: cause of disease
• Etiologic agent: agent responsible for causing
disease
• Pathogenesis: process of development of disease
• Pathogen: any microorganism that causes disease
Classifications of Disease (1 of 3)
• Congenital and hereditary diseases
– Developmental disturbances
– Causes: genetic abnormalities; abnormalities
in chromosome number or distribution;
intrauterine injury; interaction of genetic and
environmental factors
– Hemophilia (hereditary), German measles
(congenital)
Classifications of Disease (2 of 3)
• Inflammatory diseases: Body reacts to injury
through an inflammatory process
–
–
–
–
Bacteria or microbiologic agents: sore throat
Allergic reaction: hay fever
Autoimmune diseases: SLE, diabetes type 1
Unknown etiology
• Degenerative diseases
– Tissue or organ degeneration as a result of aging or
breakdown
– Arthritis, atherosclerosis
Classifications of Disease (3 of 3)
• Metabolic diseases: Disturbance in metabolic
process in body
– Diabetes, hyper- or hypothyroidism, fluid and electrolyte
imbalance
• Neoplastic diseases: Uncontrolled cell growth
– Benign: lipoma
– Malignant: Lung cancer
• Basis of classification
– 1. Similarity of lesions
– 2. Similarity of pathogenesis
• Diseases with similarities may not necessarily be
closely related
Health and Disease
– WHO (1948) – wellness is the complete state of
physical, mental and social well-being and not
simply the absence of disease and infirmity.
– Good health: more than the absence of disease
– Condition in which body and mind function
efficiently and harmoniously as an integrated
unit
• Traditional medicine: goal is to cure or
ameliorate disease.
• Modern medicine: advances relieve
suffering and advance human welfare but do
not guarantee good health.
• Allopathic medicine- usually refers to traditional
western medicine • The term allopathy was coined by the founder of
homeopathy, Samuel Hahnemann, to differentiate
homeopathic practices from conventional medicine of the
day, based on the types of treatments used. Hahnemann
used allopathy to refer to what he saw as a system of
medicine that combats disease by using remedies that
produce effects in a healthy subject that are different (hence
Greek root allo- "different") from the effects produced by the
disease to be treated.
• Contrast to Homeopathic medicine
• Preventive medicine
• Pharmaceutical
• Homeopathy is a form of alternative
medicine in which practitioners use highly
diluted preparations. Homeopathy was first
proposed by German physician Samuel
Hahnemann in 1796, based on an ipse
dixit axiom formulated by Hahnemann,
which he called the law of similars,
preparations which cause certain
symptoms in healthy individuals are given
to patients who already exhibit similar
symptoms.
• Preventive medicine or preventive care
refers to measures taken to prevent
diseases, (or injuries) rather than curing
them or treating their symptoms. The term
contrasts in method with curative and
palliative medicine, and in scope with
public health methods (which work at the
level of population health rather than
individual health).
• A pharmaceutical drug, also referred to as
medicine or medication, can be loosely defined
as any chemical substance intended for use in the
medical diagnosis, cure, treatment, or prevention
of disease
• Nutraceutical, a term combining the words
“nutrition” and “pharmaceutical”, is a food or food
product that provides health and medical benefits,
including the prevention and treatment of disease.
• Nutraceutical products may range from isolated
nutrients, dietary supplements and specific diets
to genetically engineered foods, herbal products,
and processed foods such as cereals, soups, and
beverages
Continuum of Health and Disease
Good
Health
Serious Illness
• Everyone is somewhere between the midpoint
and good health
• Good health requires active participation,
assuming responsibility for one’s health
– Eat properly, exercise, avoid harmful excesses
such as overeating, smoking, heavy drinking, or
using drugs
– Use one’s mind constructively, express emotions
appropriately, nurture a positive mental attitude
Principles of Diagnosis
• Diagnosis: determination of nature and cause of
illness
– Clinical history
– Physical examination
– Differential diagnosis
• Prognosis: eventual outcome of disease
• Treatment
– Specific treatment – directed at underlying cause
– Symptomatic treatment – alleviates symptoms but
does not influence course of disease
Clinical History (1 of 2)
• 1. History of current illness
– Severity, time of onset, and character of
patient’s symptoms
• 2. Medical history
– Details of general health and previous
illnesses that may shed light on current
problems
• 3. Family history
– Health of patient’s parents and family
members; diseases that run in families
Clinical History (2 of 2)
• 4. Social history
– Patient’s occupation, habits, alcohol and
tobacco consumption, general health, current
problems
• 5. Review of symptoms
– Symptoms other than disclosed in history of
present illness, suggesting other parts of the
body affected by disease
Physical Examination
• Physical examination
– Systematic examination of patient, with emphasis on
parts of body affected by illness
– Abnormalities noted correlated with clinical history
• Differential diagnosis
– Consideration of various diseases or conditions that
may also explain patient’s symptoms and signs
– Diagnostic possibilities narrowed by selected
laboratory tests or other diagnostic procedures
– Opinion of medical consultant may be sought
Screening Tests
• Screening tests for detection of disease
– Detect early asymptomatic diseases amenable to
treatment to prevent or minimize late-stage organ
damage
• Screening for some genetic diseases
– To screen for carriers of some genetic diseases
transmitted from parent to child as either dominant or
recessive trait
– Identifying carriers allows affected persons to make
decisions on future childbearing or management of
current pregnancy
– Example: recessive gene for sickle cell anemia in 8%
of Black population
Requirements for Effective Screening
• A significant number of persons must be at risk
for the disease in the group being screened.
• A relatively inexpensive noninvasive test must
be available to screen for the disease that does
not yield a high number of false-positive or falsenegative results
• Early identification and treatment of the disease
will favorably influence course of disease.
Examples of Screening Tests
• PPD - For TB
• PSA – Prostate Specific Antigen – For Prostate Cancer
• Alpha Fetoprotein – screening to detect certain fetal
abnormalities
• Mammogram and BRAC to detect breast cancer
• Pap Smear for cervical cancer
• Colonoscopy for Colon Cancer
• Blood Sugar test for diabetes
• Blood Pressure Determination for Hypertension
Diagnostic Tests and Procedures
(1 of 13)
• Clinical laboratory tests
– Purpose: To determine concentration of substances
in blood or urine frequently altered by disease
– Uses:
• Determine concentration or activity of enzymes in
the blood
• Evaluate function of organs
• Monitor response of certain cancers to treatment
• Detect disease-producing organisms in urine,
blood, feces
• Determine response to antibiotics
Lab Tests
Lab Tests
Lab Tests
Diagnostic Tests and Procedures
(2 of 13)
• Tests of electrical activity: to measure electrical
impulses associated with bodily functions and
activities
– ECG: measures serial changes in electrical activity of
the heart in various phases of the cardiac cycle
• Identify disturbances in heart rate, rhythm, abnormal
impulses
• Recognize heart muscle injury from ECG abnormalities
– EEG: measures electrical activity of brain; brain
waves
– EMG: measures electrical activity of skeletal muscle
during contraction and at rest
Diagnostic Tests and Procedures
(3 of 13)
• Radioisotope (radionuclide) studies: evaluate
organ function by determining rate of uptake and
excretion of substances labeled with a
radioisotope
• Uses:
– Anemia: radioisotope-labeled vitamin B12
– Hyperthyroidism: radioactive iodine
– Pulmonary blood flow: albumin; to detect presence of
blood clots
– Cancer spread: phosphorus; to determine presence
of tumor deposits in bone or spine
– Heart muscle damage: evaluate blood flow
Diagnostic Tests and Procedures
(4 of 13)
• Endoscopy
– To examine interior of body using rigid or flexible
tubular instruments equipped with lens and light
source
– To perform surgery formerly done through large
abdominal incisions
• Bronchoscope: trachea and major bronchi
• Cystoscope: bladder
• Laparoscope: abdomen
• Ultrasound
– Mapping echoes produced by high-frequency sound
waves transmitted into body; echoes reflect change in
tissue density, producing images
Diagnostic Tests and Procedures
(5 of 13)
• X-ray
– Principle: use of high-energy radiation waves at lower
doses to produce images to help diagnose disease
– Can penetrate through tissues at varying degrees
depending on tissue density
– Act on a photographic film or plate (roentgenogram)
as the rays leave the body
• Radiopaque: appears white on film; high-density
tissues such as bone absorb most of the rays
• Radiolucent: appears dark on film; low-density
tissues allow rays to pass through
Diagnostic Tests and Procedures
(6 of 13)
• X-ray can include use of contrast media to
outline structures not otherwise visualized on
standard films
–
–
–
–
–
Barium sulfate: intestinal tract
Radiopaque oil: bronchogram
Intravenous dye: intravenous pyelogram; urinary tract
Radiopaque tablets: visualize gallstones
Arteriogram: visualize blood flow, identfy narrowing or
obstruction
– Cardiac catherization: blood flow through heart,
detect abnormal communications between chambers
Diagnostic Tests and Procedures
(7 of 13)
• Computed tomographic (CT) scans
– Principle: radiation detectors record amount of X-rays
or ionizing radiation absorbed by body and feed data
into a computer that reconstructs the data into an
image
– Radiopaque and radiolucent tissues appear white and
dark as in a conventional x-ray
– Individual organs sharply demarcated by planes of fat
that appear dark because of its low density
– Delivers higher dose of ionizing radiation than x-ray
Diagnostic Tests and Procedures
(8 of 13)
• Uses of computed tomographic (CT)
scans
– Cancer screening asymptomatic individuals
– Detect abnormalities in internal organs that
cannot otherwise be identified by standard
x-ray
Diagnostic Tests and Procedures
(9 of 13)
• Magnetic resonance imaging (MRI)
– Principle: computer-constructed images of body
based on response of hydrogen protons in water
molecules when placed in a strong magnetic field
• Protons align in the direction of the magnetic field
• Protons are temporarily dislodged and wobble when
radiofrequency waves are directed at them
• Protons emit a measurable signal (resonance) that can be
used to construct images
• Intensity of resonance depends on water content of tissues,
strength and duration of radiofrequency pulse
Diagnostic Tests and Procedures
(10 of 13)
• MRI: advantages over CT scan
– Does not use ionizing radiation
– Can detect abnormalities in tissues surrounded by
bone, such as spinal cord, orbit, skull
– Bone interferes with scanning because of its density
but does not produce an image in MRI because of its
low water content
• Uses
– Multiple sclerosis
– Superior to mammography in detecting breast cancer
Diagnostic Tests and Procedures
(11 of 13)
• Positron emission tomography (PET)
– Principle: Measures metabolism of
biochemical compounds that are labeled with
positron-emitting isotopes to measure organ
function, example glucose
– Disadvantages
• Very expensive and not widely available
• Requires facilities for incorporating the isotopes
into the biochemical compound
Diagnostic Tests and Procedures
(12 of 13)
• Uses of PET
– Assess biochemical functions in brain
– Determine metabolic activities of organ or
tissue; specific site in an organ where
compound is metabolized
– Evaluate changes in blood flow in heart
muscle following a heart attack
– Distinguish benign from a malignant tumor
(increased glucose uptake in malignant
versus benign tumors)
Diagnostic Tests and Procedures
(13 of 13)
• Cytologic and histologic examinations
– Papanicolau (Pap) smear: identifies abnormal
cells in fluids or secretions; for recognizing
early changes that may be associated with
cervical and other cancers
– Biopsy: tissue samples obtained for histologic
examination to determine abnormal structural
and cellular patterns accompanying disease
• Liver, kidney, bone marrow
Radioisotope bone scan of head, chest, and pelvis
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
Ultrasound examination of 22-week-old fetus
Courtesy of Belinda Thresher
X-ray of colon with radiopaque barium sulfate
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
Bronchogram showing normal caliber and branching
of bronchi and bronchioles
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
IVP showing large cyst, right kidney
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
X-ray of gallbladder; gallstones
appear as radiolucent (dark) within
a radiopaque bile (white)
Opened gallbladder, same patient
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
Carotid angiogram, narrowing of carotid artery
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
Computed tomographic scan, CT scan
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
CT scan, chest, white nodule on left lung indicates tumor
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
CT scan, abdomen at level of kidneys, fluid-filled cysts, right kidney
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
MRI, brain, with malformation within brain stem
© Courtesy of Leonard Crowley, M.D./University of Minnesota Medical School
Discussion
• What are the underlying principles for these
diagnostic procedures: x-ray, CT scan, MRI,
PET?
• Explain the requirements for an effective
screening.
• Differentiate:
–
–
–
–
Symptomatic versus specific treatment
Sign versus symptom
Symptomatic versus asymptomatic disease
Diagnosis versus prognosis