ANDREWS’
DISEASES OF THE SKIN
Chapter 1
The Skin: Basic structure and
function
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Epidermis
dermis
Subcutaneous fat
Considerable regional variation in their
relative thickness
epidermis
• Adnexal structures, particularly follicles and
eccrine sweat units, originate during the
third month of fetal life as down growths
from the developing epidermis
• The adult epidermis is composed of three
basic cell types
– Keratinocytes
– Melanocytes
– Langerhans’ cells
Merkel cell
• Found in the basal layer of the palms and
soles, the oral and genital mucosa, the nail
bed, and the follicular infundibula
• Located directly above the BM
• Act as slow adapting touch receptors
keratinocyte
• Principal cell of the
epidermis
• Ectodermal origin
• Specialized function of
producing keratin
• Divided into the following
zones
– Basal layer
– Malphighian layer/prickle
layer
– Granular layer
– Stratum corneum
• As a cell moves upward through the
epidermis it changes morphologically
• Variation in the thickness of the different
zones of the epidermis according to skin site
• Basal cell layer is generally one cell thick
regardless of site
• During keratinization, the keratinocyte
passes through a synthetic and degradative
phase
• During the synthetic phase desmosomes are
formed
• The degradative phase is marked by the
disappearance of cell organelles and the
consolidation of all contents into a mixture
of filaments and amorphous cell envelopes
• Odland bodies found intracellularly in
upper-level keratinocytes
• Establish a barrier to water loss and with
filaggrin mediate stratum corneum cell
cohesion
Melanocyte
• Pigment producing cell
• Derived from neural crest
• Found in the fetal epidermis in the eighth
week
• Normally reside in the basal cell layer
approximately one for every 10 basal
keratinocytes
• Numbers are same regardless of race or
color
• Number and size of melanosomes
determines skin color
• Don not form desmosomal attachments with
keratinocytes
• Dendritic cell, in contact with a number of
keratinocytes, forming the epidermal
melanin unit
• Melanosomes are synthesized in the Golgi
zone
• Keratinocytes are the reservoir for melanin
in the skin
• Melanocytes in dark skin synthesize
melanosomes larger than those produced in
light skin
• The size of the melanosome is the principal
factor in determining how melanosomes
will be distributed within the keratinocyte
• Chronic sun exposure can stimulate the
melanocyte to produce larger melanosomes
• Vitiligo – destruction of melanocytes
• Albinism – melanocyte number is normal,
but because of a defect in the enzymatic
formation of melanin they are unable to
synthesize fully pigmented melanosomes
The Langerhans’ Cell
• Normally found scattered among
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keratinocytes in the stratum
spinosum/prickly cell layer
Constitute 3-5% of cells in this layer
No desmosome connections
gold chloride – appear as dendritic cells
Characterized by a folded nucleus and
distinct intracytoplasmic organelles called
Birbeck granules, which resemble a tennis
racquet
• Functionally are of the monocyte-macrophage
lineage and originate in bone marrow
• Role in induction of graft rejection, primary
contact sensitization, and immunosurveillance
• Function primarily in the afferent limb of the
immune response by providing for the
recognition, uptake, processing, and
presentation of antigens to sensitized T
lymphocytes
The Epidermal-Dermal Junction
• The junction of the epidermis and dermis is
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formed by the BMZ
Composed of four compartments
Plasma membranes of the basal cells
Lamina lucida
Basal lamina
Fibrous components associated with the
basal lamina
• BMZ is a semipermeable filter
• Serves as structural support
Epidermal Appendages: The Adnexa
• Eccrine and apocrine glands and ducts
• And pilosebaceous units
• Originate as down growths from the
epidermis
• Various adnexal structures serve specific
functions
• All can functions as reserve epidermis,
occurring principally by virtue of migration
The Eccrine Sweat Unit
• Composed of three sections
• Acrosyringium, intraepidermal component,
opens to the skin surface, called the spiral
duct
• Straight duct, dermal portion
• Secretory acinar portion, or coil gland,
found within the panniculus near the
junction of he dermis and the subcutaneous
fat
• Found at virtually all skin sites
• Most abundant on the palms, soles,
forehead, and axillae
The Apocrine unit
• Apocrine unit develops as outgrowths of the
upper portion of the hair follicle
• Straight excretory portion of he duct, opens
into the infundibular portion of the hair
follicle
• The coiled secretory gland is located at the
junction of the dermis and the subcutaneous
fat
• Composition of the product of secretion is
only partially understood
• Secretion is mediated through adrenergic
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inervation
While secretion of the gland is continuous
excretion is episodic
Gland secretion in humans serves no known
function
Generally confined to axillae, areolae,
anogenital region, EAC and the glands of
Moll on the eyelids
Do not begin to function until puberty
The Hair Follicle
• The uppermost portion of the follicle
extends from the surface opening to the
entrance of the sebaceous duct, infundibular
segment
• Isthmus, is the portion of the follicle
between the duct and the insertion of the
erector pili muscle
• The matrix includes the lowermost part of
the follicle and the hair bulb
• The hair shaft, as well as the inner and outer
root sheath, develops from the mitotically
active undifferentiated cells of the matrix
portion of the hair bulb
• The hair shaft and the inner root sheath
move together as the hair grows
• The outer root sheath remains fixed
• The cross-sectional shape of the hair depends on
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the arrangement of cells in the bulb
Basic hair color depends on the distribution of
melanosomes within hair bulb cells
Larger melanosomes are found in the hair of
blacks
Red hair is characterized by spherical
melanosomes
Graying of hair results from decreased melanocyte
numbers
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Anagen
Catagen
Telogen
Average period of growth of scalp hair is 3
to 4 years, involutional and resting phases
last approx 3 months
• 85 to 90% of scalp hairs are in anagen phase
The Sebaceous Gland
• Formed embryologically as an outgrowth
from the upper portion of the hair follicle
• Found in greatest abundance on the face and
scalp
• Distributed throughout all skin sites except
palms and soles
• Always associated with hair follicles except
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at at the following sites:
Eyelids (meibomian glands)
Buccal mucosa and vermilion border of the
lip (Fordyce’s spots)
Prepuce (Tyson’s glands)
Female areolas (Montgomery’s tubercles)
The Nails
• Matrix keratinization leads to the formation
of the nail plate
• Keratin types found in the nail are a mixture
of epidermal and hair types
• Fingernails grow an average of 0.1 mm/day,
slower for toenails
• Abnormalities may serve as important clues
to cutaneous and systemic disease
The Dermis
• The constituents of the dermis are of mesodermal
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origin, with the exception of nerves
By the 12th week of fetal life fibroblasts are
actively synthesizing reticulum fibers, elastic
fibers, and collagen
The principal component of the dermis is collagen
This serves as the major structural protein for the
entire body
Represents 70% of the dry weight of the skin
• The fibroblast synthesize procollagen
molecules that are secreted and assembled
into collagen fibrils
• Collagen is rich in the amino acids
hydroxyproline, hydroxylysine and glycine
• Collagen fibers are loosely arranged in the
upper dermis
• Tightly bundled in a fascicle-like pattern in
the lower dermis
• Type IV collagen is found in the BMZ
• Type VII collagen is the major structural
component of anchoring fibrils and is
produced predominantly by keratinocytes
• Fibroblast also synthesize elastic fibers, as
well as the ground substance of the dermis
• Amino acids desmosine and isodesmosine
are unique to elastic fibers
• Collagen is the major stress-resistant
material of the skin
• Elastic fibers contribute very little to
resisting deformation and tearing of the
skin, but have a role in maintaining
elasticity
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Defects in collagen synthesis
Ehlers-Danlos syndrome
X-linked cutis laxa
Osteogenesis imperfecta
Defects in elastic tissues
Vasculature
• Consists principally of two
intercommunicating plexuses
• Subpapillary plexus/upper horizontal
network
• Lower horizontal plexus
Muscles
• Smooth muscle occurs in the skin as
arrectores pilorum, as the tunica dartos of
the scrotum , and in the areolas around the
nipples
• Striated muscle occurs in the skin of the
neck as the platysma and in the skin of the
face as the muscles of facial expression
• Glomus bodies, specialized aggregates of
smooth muscle cells found between
arterioles and venules
Nerves
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Dermis is rich in nerves
Meissner corpuscles, touch and pressure
Vater-Pacini corpuscles
Temperature, pain and itch sensation are
transmitted by unmyelinated nerve fibers
which terminate in the papillary dermis and
around hair follicles
Mast Cells
• 6-12 microns in diameter
• Contain up to 1000 granules
• cell surface contains glycoprotein receptor
sites for IgE
• High content of heparin
• Also contain histamine, neutrophil
chemotactic factor, eosinophil chemotactic
factor of anaphylaxis, tryptase, kininogenase,
and betaglucoseaminidase
Dermal Dendrocyte
• Possesses phenotypic characteristics of
macrophages
• Found in a perivascular network and may
serve as an antigen presenting cell
Subcutaneous Tissue
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Beneath the dermis lies the panniculus
Subcutaneous tissue thickness varies
Panniculitides affect this level of the skin
The pattern of inflammation, specifically
whether it primarily affects the septa or the
fat lobules themselves, serves to distinguish
the various conditions
CUTANEOUS
SYMPTOMS,SIGNS, AND
DIAGNOSIS
Chapter 2
• The same disease may show variations
under different conditions and in different
individuals
• Appearance of lesions may have been
modified by previous treatment or obscured
by extraneous influences (scratching,
secondary infection)
• Subjective symptoms may be the only
evidence of disease
CUTANEOUS SYMPTOMS
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Pruritis
Burning
Tingling
Prickling
Biting
Formication
Pain
numbness
Pruritis
• An unpleasant cutaneous sensation which
provokes the desire to scratch or rub the
skin
• Most common cutaneous symptom
• Carried from the skin by unmyelinated C
fibers
• The quality of the itch may be useful in
determining the diagnosis
• Regional and individual differences in the
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perception of and the reaction to pruritis
May be in part related to the psychologic
state at the time
The anogenital area is especially prone to
pruritis
Xerosis
Pruritis with HIV and AIDS
• Pruritis with systemic disease
• Hepatobiliary diseases, especially biliary
obstructive disease, severe renal
insufficiency, iron-deficiency anemia,
endocrine disorders, and internal
malignancy (especially lymphoma)
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Thyroid dysfunction
Less commonly parathyroid
DM
Is typically generalized when associated
with renal failure (uremic pruritis)
• Often associated with the appearance of
hyperkeratotic prurigo nodulelike lesions
• Kyrle’s disease/perforating disorder of renal
failure or dialysis
• Pruritis of live disease
• An associated hepatitis C virus infection
should always be sought
• Opiate antagonists may improve this form
of pruritis
• Antidepressants, belladonna, alkaloids,
opiates, and oral contraceptives may induce
pruritis
• Recreational drugs (amphetamines and
cocaine)
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Psychologic disease
Most frequently anxiety/depression
Or obsessive compulsive disorder
Treat the underlying disorder
Other symptoms
• Pain
• Allodynia, production of pain by normally
trivial stimuli, PHN
• Hypesthesia and hyperesthesia
• Loss of specific sensations, Hansen’s
disease and follicular mucinosis
• Reversal of the perception of heat and cold,
Ciguatera fish poisoning
CUTANEOUS SIGNS
PRIMARY LESIONS
Macules, patches, papules, plaques,
nodules, tumors, wheals, vesicles,
bullae, and pustules
Macules
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Variously sized
Circumscribed changes in the skin color
Without elevation or depression
Circular oval or irregular
Patches
• A large macule
• 1 cm or greater in diameter
• Nevus flammeus or vitiligo
Papules
• Circumscribed, solid elevations, with no
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visible fluid, varying in size from pinhead
to 1 cm
May be acuminate, rounded, flat-topped,
conical, or umbilacated
Variety of colors
May be soft or firm
Papulosquamous, when capped by scales
• May be discrete and irregularly distributed
or grouped
• Some persist and some progress
Plaques
• A broad papule or a confluence of papules
• 1 cm or more in diameter
• Generally flat but may be depressed
Nodules
• Morphologically similar to papules
• More than 1 cm in diameter
• Most frequently are centered on the dermis
or the subcutaneous fat
Tumors
• Soft or firm freely moveable or fixed
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masses
Various sizes and shapes
Generally greater than 2 cm in diameter
Elevated or deep seated
Pedunculated
Wheals
• Evanescent, edematous, plateaulike
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elevations of various sizes
Usually oval or arcuate contours
Pink to red
Surrounded by a pink areola
May be discrete or coalesce
Vesicles
• Circumscribed, fluid-containing, epidermal
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elevations 1 to 10 mm
Pale or yellow from serous exudate, or red
Apex may be rounded, acuminate, or
umbilacated
Discrete, irregularly scattered, grouped or
linear
May develop into bullae or pustules
Vesicopustules
Unilocular or multilocular
Bullae
• Rounded or irregularly shaped blisters
containing serous or seropurulent fluid
• Differ from vesicles only in size, being
larger than 1 cm
• Typically unilocular
• May be located superficially in the
epidermis or subepidermal
• Nikolsky’s sign, diagnostic maneuver of
putting lateral pressure on unblistered skin
in a bullous eruption with shearing of the
epithelium
• Absoe-Hansen’s sign, extension of a blister
to adjacent unblistered skin when pressure
is put on top of the blister
• Cellular contents of the bullae may be
useful in confirming the diagnosis
Pustules
• Small elevations of the skin containing
purulent material (usually necrotic
inflammatory cells)
• Similar to vesicles and have an
inflammatory areola
• White, yellow or red if they contain blood
• May originate as pustules or develop from
papules or vesicles
SECONDARY LESIONS
Scales, crusts, erosions, ulcers,
fissures, and scars
Scales
• Dry or greasy laminated masses of keratin
• When the formation of epidermal cells is
rapid or the process of normal keratinization
is interfered with, pathologic exfoliation
results, producing scales
• Vary in size
• Vary in color
• May have a silvery sheen from trapping of
air between their layers: these are
micaceous scales, characteristic of psoriasis
Crusts
• Crusts are dried serum, pus, or blood,
usually mixed with epithelial and
sometimes bacterial debris
• Vary greatly in size, thickness, shape and
color, according to their origin, composition
and volume
• When they become detached the base may
be dry or moist
Excoriations and abrasions
• An excoriation is a punctate or linear
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abrasion produced by mechanical means,
usually involving only the epidermis, but
not uncommonly reaching the papillary
layer of the dermis
Caused by scratching
If the damage is a result of mechanical
trauma or constant friction – abrasion
Frequently has an inflammatory areola
May provide access for pyogenic organisms
Fissures
• A fissure is a linear cleft through the
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epidermis , or into the dermis
May be single or multiple
Microscopic to several centimeters in length
Sharply defined margins
May be dry, moist, red, straight, curved,
irregular, or branching
Erosions
• Loss of all or portions of the epidermis
alone
• May not become crusted
• Heals without a scar
Ulcers
• Rounded or irregularly shaped excavations
that result from complete loss of the
epidermis plus some of the portions of the
dermis
• Various sizes, shallow or deep
• Heal with scarring
Scars
• Composed of new connective tissue that
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replaced lost substance in the dermis or
deeper parts as a result of injury or disease,
as part of the normal reparative process
Characteristic of certain inflammatory
processes
Scars may be thin and atrophic or keloids
May be smooth or rough, pliable or firm
Pink initially, later becoming white and
glistening
GENERAL DIAGNOSIS
history
• Patients age, health, occupation, hobbies, living
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conditions
Onset, duration and course of the disease
Previous treatment
Family history
Drug history
Other illness, travel abroad, home and work
environment, seasonal occurrences and
recurrences
Sexual orientation and practices
examination
• Natural sunlight is ideal
• Fluorescent bulbs that produce wavelengths
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of light closer to natural sunlight
Wood’s light
Magnifying lens
Palpation
Scraping
View entire eruption, no “Peek-a boo” exam
Diagnostic Details of Lesions
distribution
• Lesions may be few or numerous, and in
arrangement they may be discrete or may
coalesce to patches of peculiar
configuration
• Lines of cleavage – PA
• Dermatomes – Zoster
• Blaschko’s lines – epidermal nevi
evolution
• Some lesions appear fully evolved
• Others develop from smaller lesions, then
may remain the same during their entire
existence
• A polymorphous eruption with lesions in
various stages of development or involution
may be present , varicella
involution
• Lesions may disappear completely
• May leave characteristic residual
pigmentation or scarring
grouping
• Characteristic of DH, herpes simplex,
herpes zoster, and late syphilitic eruptions
• Corymbose, small lesions around a larger
one
• Linear (breakfast-lunch-and-dinner), flea
and other arthropod bites
• Agminated, grouped lesions of various sizes
configuration
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Linear, lesion in a line
Annular, forming a complete circle
Arcuate, portion of a circle
Polycyclic, composed of several intersecting
portions of circles
Serpiginous, not straight but not forming parts of
circles
Guttate, small, like drops
Nummular, larger, like a coin
Unusual configurations may be exogenously
induced
color
• The Tyndall effect modifies the color of the
skin and the color of the lesions by the
selective scattering of light waves of
different wave-lengths. The blue nevus and
mongolian spots are examples of this light
dispersion effect
• Not advisable to place too much reliance on
color
• Patches lighter in color than normal skin
may be completely depigmented or have
lost only part of their pigment
• Hyperpigmentation may be a result of
epidermal or dermal causes
• Hyperpigmentation following inflammation
is most commonly the result of dermal
melanin deposition
consistency
• Palpation is an essential part of the physical
examination of lesions
• Blanch? Fluctuant? Hot or cold? Firm or
calcified? Brawny? Doughy?
Cutaneous Findings in Systemic
Disease
At times an unusual skin eruption
may be a clue to some internal
disorder that may not be obvious.
nodules
• Subcutaneous or dermal metastatic nodules
are common and easily detected
manifestations of metastatic carcinoma
• Most favored site is trunk or scalp
• Frequently metastases are from carcinoma
of the breast, GI tract, melanoma, ovary,
uterus
• Sister Mary Joseph’s nodule
• Multicentric reticulohistiocytosis, internal
malignancy may be present in up to 25 % of
cases
• Gardner’s syndrome, fibromas, epidermoid
cysts, osteomas, and desmoid tumors
vascular lesions
• Petechiae, ecchymoses, “pinch purpura”
and caput medusae are some of the vascular
lesions associated with malignancies
• “pinch purpura’, primary systemic
amyloidosis of the skin
• systemic steroid treatment ma result in easy
bruisability
flushing
• Episodic flushing, especially on the face,
lasting some 10 to 30 minutes, is a
consistent sign of carcinoid syndrome
• Bronchial carcinoid tumors
pruritis
• Generalized pruritis may be seen in many
myeloproliferative diseases, but it is most
characteristic or lymphoma or polycythemia
vera
• Liver disease, renal failure, iron deficiency,
thyroid or parathyroid disease
eczema
• Unilateral eczematous eruption on one
nipple, may be Paget’s disease of the breast
with underlying intraductal carcinoma
• Early manifestation of MF may resemble an
eczema
• Bazex’s syndrome, an eczematous eruption
involving the hands, feet, nose, and ears, a
sign of an underlying malignant neoplasm
of the aerodigestive tract
vesicles and bullae
• Dermatitis herpetiformis
• Associated with a usually asymptomatic
gluten-sensitive enteropathy
• Increased risk for the development of
gastrointestinal lymphoma
• zoster
erythroderma
• Universal erythroderma, generally
accompanied by scaling, may be associated
with malignancy, usually lymphoma
• Characteristic of Sezary syndrome
• Severe drug eruption may be the cause
erythema and edema
• Erythema, edema, and purple discoloration
of the eyelids, indicative of
dermatomyositis
• Gottron’s papules
• Skin lesions can precede the myositis by
weeks to years
• Tender, erythematous, edematous plaques
that may centrally vesiculate on the upper
part of the body associated with fever and
leukocytosis characterize Sweet’s syndrome
• May be presenting sign of myelogenous
leukemia
erythematous nodules
• Erythema nodosum may rarely be
associated with Hodgkin’s disease and
metastatic carcinoma
• Most common cause is preceding
streptococcal pharyngitis
hyperkeratosis
• Sezary’s erythroderma, Hodgkin’s disease,
lymphocytic leukemia and Bazex’s
syndrome may be accompanied by
hyperkeratosis of the palms and soles
• Howel-Evans’ syndrome, a hereditary
esophageal carcinoma syndrome
hyperpigmentation
• Diffuse melanosis cutis, in metastatic
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melanoma. Melanuria is also present
Pituitary tumors
Addison’s disease
Hemochromatosis and arsenic intoxication,
bronze hyperpigmentation
Acanthosis nigricans
alopecia
• When follicular mucinosis occurs in lesions
of mycosis fungoides, affected areas on the
scalp or beard may present with sharply
circumscribed plaques of alopecia
• May also occur in syphilis, thyroid disease,
and iron deficiency
hirsutism and hypertrichosis
• Adrenal or ovarian carcinomas maybe the
cause of excessive hair growth
• Malignant down is an excessive growth of
lanugo-like hair, which is assoc with
malignant disease of the lung, colon,
gallbladder, and uterus
urticaria
• Hodgkin’s disease may be accompanied by
urticaria
• Cold urticaria with cryoglobulinemia is seen
in multiple myeloma
sulfer-yellow plaques on the
shins
• Necrobiosis lipoidica (with or without
diabetes) presents as bilateral, well-defined
plaques with a smooth, glistening surface
and yellow color
The end