Dermatopathology

A, Subcorneal (as in pemphigus foliaceus). B, Suprabasal (as in pemphigus vulgaris). C, Subepidermal (as in bullous pemphigoid & dermatitis herpetiformis). Assessment of the levels of epidermal separation forms the basis of the initial differential diagnosis of these lesions.
Levels of blister formation


A, Pemphigus vulgaris. There is uniform deposition of immunoglobulin and complement (green) along the cell membranes of keratinocytes, producing a characteristic "fishnet" appearance. B, The immunoglobulin deposits are more superficial in pemphigus foliaceus.
Pemphigus direct IF microscopy

Pemphigus vulgaris

Suprabasal acantholysis results in an intraepidermal blister containing rounded keratinocytes that are separating from their neighbors. Initially, a single row of basal cells is present on the floor of the blister with dermal papillomatosis (tombstone effect). Follicular involvement by acantholysis is also common.

There is subcorneal acantholysis leading to suncorneal blister.

Pemphigus foliaceus

P. Vulgaris

Extensive erosions and blistering on the front of the knee.

P. Vulgaris intact and ruptured blisters

Umblical lesions showing intact blisters as well as raw erosions

P. Foliaceus

Blisters are much less erosive than those seen in pemphigus vulgaris, since the level of the blisters is more superficial (subcorneal). In this patient, the disease was induced by penicillamine therapy, and there are intact blisters, erosions, and crusting. Picture on Rt. & below are close-up views.

Bullous pemphigoid

Tense, fluid-filled blisters result from vacuolization of the basal layer, producing subepidermal blisters
Bullous pemphigoid

The subepidermal vesicle has an inflammatory infiltrate rich in eosinophils

In bullous pemphigoid, both IgG antibody and complement can be detected by direct immunofluorescence as a linear band outlining the subepidermal basement membrane zone

Upper Lt. Lesions consist of intact and eroded (usually scratched) erythematous blisters, often grouped (seen here on elbows and arms). Upper Rt. The blisters are associated with basal cell layer injury initially caused by accumulation of neutrophils (microabscesses) at the tips of dermal papillae. Lower Rt. Selective deposition of IgA autoantibody at the tips of dermal papillae is characteristic.
Dermatitis herpetiformis


Dermatitis herptiformis
Extensive lesions on the extensor aspects of the forearms

Dermatitis herpetiformis

Dermatitis herptiformis


The dermal papillae are distended by microabscesses of neutrophils and fibrin. there is evidence of early vesiculation.
Dermatitis herptiformis


Part of an established subepidermal blister containing edema fluid, fibrin and neutrophils.
Dermatitis herptiformis


Dermatitis herpetiformis. A, Papillary dermal microabscesses are associated with zones of dermoepidermal cleavage that eventually coalesce to form a clinical blister. B, By direct immunofluorescence, these abscesses are rich in IgA and fibrin deposits.
Dermatitis herptiformis