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CLASSIFICATION OF SKIN DISEASES
Skin diseases are identified and classified
according to characteristic lesions (size, shape,
color & location) and other signs and symptoms
Pruritis – itching
Edema – swelling
OR LARGER FLUID-FILLED
DISORDERS OF EPIDERMAL MATURATION
Most ichthyoses become apparent either at or
around the time of birth.
Acquired (noninherited) variants also exist; in the
acquired ichthyosis vulgaris in adults, there can
be an association with lymphoid and visceral
Primary categories include ichthyosis
vulgaris (autosomal dominant or acquired),
erythroderma (autosomal recessive), lamellar
ichthyosis (autosomal recessive), and X-linked
Urticaria (hives) is a common disorder of the skin
characterized by localized mast cell degranulation
and resultant dermal micro vascular hyper
This gives rise to pruritic oedematous plaques
Angioedema is closely related to urticaria and is
characterized by deeper oedema of both the
dermis and the subcutaneous fat.
The Greek word eczema, meaning "to boil over,"
acute eczematous dermatitis.
All forms of eczema are characterized by red,
papulovesicular, oozing, and crusted lesions that,
if persistent, develop into raised, scaling plaques
due to reactive acanthosis and hyperkeratosis
Based on initiating factors, eczematous dermatitis
can be subdivided into the following categories:
(1) allergic contact dermatitis, (2) atopic
dermatitis, (3) drug-related eczematous
dermatitis, (4) photoeczematous dermatitis, and
(5) primary irritant dermatitis
A, Acute allergic contact dermatitis, with numerous
vesicles on erythematous skin due to antigen exposure
B, Histologically, intercellular edema within the
epidermis creates small, fluid-filled intraepidermal
Spongiosis characterizes acute eczematous dermatitis,
hence the histologic synonym spongiotic dermatitis.
Unlike urticaria, in which edema is restricted to the
superficial dermis, edema seeps into the intercellular
spaces of the epidermis, splaying apart keratinocytes,
particularly in the stratum spinosum.
A, The target-like clinical lesions
consist of a central blister or zone
of epidermal necrosis surrounded
by macular erythema
B, Early lesions show
lymphocytes collecting along the
dermoepidermal junction where
basal keratinocytes have begun to
become vacuolated. 19
Erythema multiforme is an uncommon, self-limited disorder that
seems to be a hypersensitivity reaction to certain infections and
(1) infections such as herpes simplex, mycoplasmal infections,
histoplasmosis, coccidioidomycosis, typhoid, and leprosy,
(2) administration of certain drugs (sulfonamides, penicillin,
barbiturates, salicylates, hydantoins, and antimalarial);
(3) malignant disease (carcinomas and lymphomas); and
(4) collagen vascular diseases (lupus erythematosus,
dermatomyositis, and polyarteritis nodosa
An extensive and symptomatic febrile form of the disease, which is
often but not exclusively seen in children, is called Stevens-
Typically, erosions and haemorrhagic crusts involve the lips and
oral mucosa, although the conjunctiva, urethra, and genital and
perianal areas may also be affected.
Secondary infection of involved areas due to loss of skin integrity
may result in life-threatening sepsis.
Another variant, termed toxic epidermal necrolysis, results in
diffuse necrosis and sloughing of cutaneous and mucosal epithelial
surfaces, producing a clinical situation analogous to an extensive
burn when both infection and fluid loss are clinical concerns 21
Oil drop sign
Psoriasis is a common chronic inflammatory
dermatosis affecting as many as 1% to 2% of
Persons of all ages may develop the disease.
Psoriasis is sometimes associated with arthritis,
myopathy, enteropathy, spondylitic joint disease,
or the acquired immunodeficiency syndrome.
Psoriatic arthritis may be mild or may produce
severe deformities resembling the joint changes
seen in rheumatoid arthritis
Increased epidermal cell turnover results in marked
epidermal thickening (acanthosis), with regular
downward elongation of the rete ridges sometimes
described as appearing like test tubes in a rack
Mitotic figures are easily identified well above the basal
cell layer, where mitotic activity is confined in normal
The stratum granulosum is thinned or absent, and
extensive overlying parakeratotic scale is seen
Seborrheic dermatitis is a chronic inflammatory
dermatosis even more common than psoriasis,
affecting 1% to 3% of the general population.
It classically involves regions with a high density
of sebaceous glands, such as the scalp, forehead
(especially the glabella), external auditory canal,
retro auricular area, nasolabial folds, and the
The individual lesions are macules and papules on
an erythematous-yellow, often greasy base,
typically in association with extensive scaling and
Fissures may also be present, particularly behind
Oily scalp, with scales that form from excess sebum
Can spread to face, ears & eyebrows
Pruritic, purple, polygonal, planar papules, and
plaques" are the tongue-twisting "six p's" of this
disorder of skin and mucosa.
Lichen planus is usually self-limited and most
commonly resolves spontaneously 1 to 2 years after
onset, often leaving zones of post inflammatory
Oral lesions may persist for years. Squamous cell
carcinoma has been noted to occur in chronic
mucosal and paramucosal lesions of lichen planus,
Flat-topped pink-purple, polygonal papule has a white
lacelike pattern that is referred to as
Biopsy specimen demonstrating a bandlike infiltrate of
lymphocytes at the dermoepidermal junction,
hyperkeratosis, hypergranulosis and pointed rete ridges
(sawtoothing) as a result of chronic basal cell layer
Lichen planus is characterized
histologically by a dense, continuous
infiltrate of lymphocytes along the
dermoepidermal junction, a prototypic
example of interface dermatitis .
Anucleate, necrotic basal cells may
become incorporated into the inflamed
papillary dermis, where they are referred to
as colloid or Civatte bodies.
Pemphigus is a blistering disorder caused
by autoantibodies that result in the dissolution of
intercellular attachments within the epidermis and
The majority of individuals who develop pemphigus are
in the fourth to sixth decades of life, and men and women
are affected equally.
There are multiple variants: (1) pemphigus vulgaris, (2)
pemphigus vegetans, (3) pemphigus foliaceus, (4)
pemphigus erythematosus, and (5) paraneoplastic
Histologic levels of blister formation.
A, In a sub corneal blister the stratum corneum forms
the roof of the bulla (as in pemphigus foliaceus).
B, In a suprabasal blister a portion of the epidermis,
including the stratum corneum, forms the roof (as in
C, In a sub epidermal blister the entire epidermis
separates from the dermis (as in bullous pemphigoid).
Pemphigus vulgaris, by far the most common
type (accounting for more than 80% of cases
worldwide), involves the mucosa and skin,
especially on the scalp, face, axilla, groin,
trunk, and points of pressure.
It may present as oral ulcers that may persist
for months before skin involvement appears.
Pemphigus vegetans is a rare form that usually
presents not with blisters but with large, moist,
verrucous (wart-like), vegetating plaques
studded with pustules on the groin, axillae, and
A, Eroded plaques are formed on rupture of confluent,
thin-roofed bullae, here affecting axillary skin.
B, Suprabasal acantholysis results in an intraepidermal
blister in which rounded (acantholytic) epidermal cells
are identified (inset).
C, Ulcerated blisters in the oral mucosa are also
common as seen here on the mucosal portion of the lip.
A, THE DELICATE, SUPERFICIAL (SUB CORNEAL)
BLISTERS ARE MUCH LESS EROSIVE THAN SEEN IN
B, SUB CORNEAL SEPARATION OF THE EPITHELIUM IS
Direct immunofluorescence of pemphigus.
A, In pemphigus vulgaris there is deposition of
immunoglobulin along the plasma membranes of
epidermal keratinocytes in a reticular or fishnet-like
Also note the early suprabasal separation due to loss of
cell-to-cell adhesion (acantholysis).
B, In pemphigus foliaceus the immunoglobulin deposits
are more superficial.
A, Clinical bullae result from basal cell layer
vacuolization, producing tense, intact subepidermal
blisters that are difficult to rupture given the roof
formed by the full thickness of the epidermis.
Ulceration results upon rupture as the blisters are
B, Histopathology shows an intact blister with
eosinophils, as well as lymphocytes and occasional
neutrophils, that may be intimately associated with
basal cell layer destruction and the creation of the
Linear deposition of complement along the
dermoepidermal junction in bullous pemphigoid;
the pattern has been likened to ribbon candy.
Epidermolysis bullosa constitutes a group of
disorders caused by inherited defects in structural
proteins that lend mechanical stability to the skin.
The common feature is a proclivity to form blisters
at sites of pressure, rubbing, or trauma, at or soon
A, Junctional epidermolysis bullosa showing typical
erosions in flexural creases.
B, A noninflammatory subepidermal blister has
formed at the level of the lamina lucida.
Dermatitis herpetiformis is a rare disorder characterized
by urticaria and grouped vesicles.
The disease affects predominantly males, often in the
third and fourth decades. In some cases it occurs in
association with intestinal celiac disease and responds to
a gluten-free diet.
A, The blisters are associated with basal cell layer injury
initially caused by accumulation of neutrophils
(microabscesses) at the tips of dermal papillae.
B, Selective deposition of IgA autoantibody at the tips of
dermal papillae is characteristic.
C, Lesions consist of intact and eroded (usually
scratched) erythematous blisters, often grouped (seen
here on elbows and arms).
Acne is a disorder of pilosebaceous follicles causing
comedones,papules and pustules on the face ,chest and upper back
Affects many adolescents, about 80% between the ages of 12 – 15.
Result of hormonal changes that occur at puberty
SEBACEOUS GLANDS increase secretion of SEBUM, the oily fluid that
is released through the hair follicles. 61
Virtually universal in the middle to late
teenage years, acne vulgaris affects both
males and females, although males tend to
have more severe disease.
Acne is seen in all races but is usually milder
in people of Asian descent.
Acne vulgaris in adolescents is believed to
occur as a result of physiologic hormonal
variations and alterations in hair follicles,
particularly the sebaceous gland. 62
Acne is divided into noninflammatory and
inflammatory types, although the types may
coexist. The former consists of open and closed
Open comedones are small follicular papules
containing a central black keratin plug. This
colour is the result of oxidation of melanin
pigment (not dirt).
Closed comedones are follicular papules without
a visible central plug.
Inflammatory acne is characterized by
erythematous papules, nodules, and pustules .
A, INFLAMMATORY ACNE ASSOCIATED WITH ERYTHEMATOUS
PAPULES AND PUSTULES.
B, A HAIR SHAFT PIERCES THE FOLLICULAR EPITHELIUM,
ELICITING INFLAMMATION AND FIBROSIS.
C, OPEN COMEDON
Closed comedones (whiteheads) If duct
blocked by dirt or dead cells, the sebum
accumulates, causing a whitehead
Open comedones (blackheads)Sebaceous
accumulation at the surface becomes oxidized
and turns black, causing a blackhead
Once propionibacterium acnes (that’s always
present on the skin)enters the broken skin, pus
forms and a pimple or pustule results.
Squeezing the pimple spreads the infection
Soft nodules that are secondary comedones
from repeated ruptures and reencapsulations
Painful and disfiguring.
Rosacea is a common disease of middle age and
beyond, affecting up to 3% . with a predilection for
females. Four stages are recognized:
(1) flushing episodes (pre-rosacea),
(2) persistent erythema and telangiectasia,
(3) pustules and papules, and
(4) rhinophyma-permanent thickening of the nasal skin
by confluent erythematous papules and follicular
Panniculitis is an inflammatory reaction in the
subcutaneous adipose tissue that may
preferentially affect (1) the connective tissue
septa separating lobules of fat, or (2) the lobules
of fat themselves.
Verrucae are common lesions of children and
adolescents, although they may be
encountered at any age.
They are caused by human papillomaviruses.
Transmission of disease usually involves
direct contact between individuals or auto-
Verrucae are generally self-limited, regressing
spontaneously within 6 months to 2 years.
A, Multiple papules with rough pebble-like surfaces.
B (low power) and C, (high power) histology of the
lesions showing papillomatous epidermal hyperplasia
and cytopathic alterations that include nuclear pallor
and prominent keratohyaline granules.
D, In situ hybridization demonstrating viral DNA within
Molluscum contagiosum is a common, self-limited viral
disease of the skin caused by a poxvirus.
The virus is characteristically brick shaped, has a
dumbbell-shaped DNA core, and measures 300 nm in
maximal dimension, and thus represents the largest
pathogenic poxvirus in humans and one of the largest
viruses in nature.
Infection is usually spread by direct contact,
particularly among children and young adults
BACTERIAL SKIN INFECTIONS
The most common bacterial skin infections are:
WHERE SCABIES IS MAINLY
In between the fingers
Around the head and neck
Itching a scabies rash can make the infection
Scabies is passed from one person to another
Scabies only affects the skin, outside the body.
Sever pruritus is the hallmark of scabies.
extreme itching, which can worse at night and after
As opposed to deep fungal infections of the skin,
where the dermis or sub cutis is primarily involved,
Superficial fungal infections of the skin are confined to
the stratum corneum, and are caused primarily by
These organisms grow in the soil and on animals and
produce a number of diverse and characteristic clinical
Tinea capitis usually occurs in children and is only
rarely seen in infants and adults.
Tinea barbae is a dermatophyte infection of the
beard area that affects adult men; it is a relatively
Tinea corporis, on the other hand, is a common
superficial fungal infection of the body surface that
affects persons of all ages, but particularly
Tinea cruris occurs most frequently in the inguinal
areas of obese men during warm weather. Heat,
friction, and maceration all predispose to its
Tinea pedis (athlete's foot) affects 30% to 40% of the
population at some time in their lives.
There is diffuse erythema and scaling, often initially
localized to the web spaces.
Most of the inflammatory tissue reaction, however, has
recently been shown to be the result of bacterial super
infection and not directly related to the primary
Spread to or primary infection of the nails is referred to
This produces discoloration, thickening, and deformity of
the nail plate
Tinea versicolor is caused by a
yeast called Malassezia furfur
lives in the skin of most adults i.e. it is part of normal flora.
This exists in two forms, one of which causes visible spots.
Factors that can cause the fungus to become more visible
include high humidity and immune or hormone
However, almost all people with this very common condition
are perfectly healthy.
fungus is part of the normal adult skin, this condition is not
contagious. It often recurs after treatment.
There may be mild eczematous dermatitis associated with
intraepidermal neutrophils .
Fungal cell walls, rich in mucopolysaccharides, stain
bright pink to red with periodic acid-Schiff stain.
They are present in the anucleate cornified layer of
lesional skin, hair, or nails