Pemphigus Foliaceus
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Direct answer
Pemphigus foliaceus is a superficial variant of pemphigus caused by autoantibodies against desmoglein 1, a cadherin expressed in the upper epidermis, producing very fragile subcorneal blisters that rupture almost immediately, leaving scaly, crusted, erosive lesions on the seborrhoeic areas of the trunk, face and scalp. Because desmoglein 1 is minimally expressed in oral mucosa (where desmoglein 3 predominates and compensates), the mouth is characteristically spared — the opposite of pemphigus vulgaris. Diagnosis rests on ELISA for anti-desmoglein 1 antibodies, histology showing superficial acantholysis high in the epidermis, and granular intercellular IgG/C3 on direct immunofluorescence.
What you must remember
- Target antigen and level: anti-desmoglein 1 autoantibodies split the epidermis at or just below the granular layer (subcorneal or superficial acantholysis), so intact blisters are rarely seen — crusts, scales and shallow erosions dominate.
- Morphology and sites: loose, thin-roofed flaccid bullae that break easily; scaly, crusted, well-demarcated erythematous patches in a seborrhoeic distribution — scalp, face, chest, upper back and shoulders.
- Mucosal involvement: oral and other mucosae are typically spared because mucosa expresses desmoglein 3 which can compensate for desmoglein 1 loss — a high-yield contrast with pemphigus vulgaris.
- Nikolsky sign: mechanical pressure slides the superficial epidermis away — positive, as in other pemphigus; the bulla-spread sign may also be positive.
- Endemic form: fogo selvagem (wild fire) in rural South America (Brazil), affecting the young, with an environmental trigger proposed on epidemiological grounds (exposure to insects such as Simulium black flies has been implicated in several studies) on a genetic background; clinically and immunologically similar to sporadic pemphigus foliaceus.
- Related superficial variants: pemphigus erythematosus (Senear-Usher syndrome) — lupus-like malar rash in seborrhoeic distribution with immunofluorescence showing both intercellular and basement-membrane-zone staining; drug-induced pemphigus foliaceus from penicillamine or captopril; and IgA pemphigus as a separate entity.
- Diagnosis: ELISA anti-Dsg1 titres track activity; histology — superficial split with acantholytic cells in the upper epidermis; direct immunofluorescence — intercellular (fish-net) IgG and C3 deposition throughout the epidermis.
- Treatment: topical steroids and sun protection for localised disease; systemic corticosteroids (often lower doses than in vulgaris) with steroid-sparing agents such as azathioprine, mycophenolate or methotrexate; prognosis is better than pemphigus vulgaris, and some cases remit.
Common confusion
The exam repeatedly contrasts pemphigus foliaceus with pemphigus vulgaris (deep suprabasal split, anti-desmoglein 3, oral erosions usual, more severe) and with bullous impetigo (staphylococcal exfoliative toxin cleaves desmoglein 1 identically, producing similar superficial crusts — bullous impetigo is localised, cropped, culture-positive and lacks intercellular IgG). Its crusted facial and scalp lesions are also mislabelled as seborrhoeic dermatitis or impetiginised eczema; the keys are the superficial acantholysis on histology, positive Nikolsky sign and intercellular immunofluorescence.
Exam-focused takeaway
The signature question gives a crusted, scaly seborrhoeic eruption with an intact mouth and asks for the antigen (desmoglein 1) or the level of split (subcorneal/granular layer). Fogo selvagem and its Brazilian rural setting, the Senear-Usher overlap with lupus, and the "desmoglein compensation" explanation for mucosal sparing are standard one-liners. Keep the comparison triplet ready: foliaceus (Dsg1, superficial, mouth spared), vulgaris (Dsg3 ± Dsg1, suprabasal, mouth involved), bullous impetigo (toxin-mediated Dsg1 cleavage, no autoantibodies).
Frequently asked questions
Which antigen is targeted in pemphigus foliaceus?
Desmoglein 1, a desmosomal cadherin concentrated in the superficial epidermis; antibody binding splits the skin at the granular or subcorneal level.
Why are oral lesions absent in pemphigus foliaceus?
Oral mucosa expresses little desmoglein 1 but abundant desmoglein 3, which maintains intercellular adhesion there even when desmoglein 1 is blocked — the desmoglein compensation concept.
What is fogo selvagem?
The endemic form of pemphigus foliaceus occurring in rural Brazil and neighbouring areas, affecting children and young adults, with a proposed environmental insect-linked trigger; it means "wild fire" for its burning character.
How does histology differ from pemphigus vulgaris?
Foliaceus shows acantholysis and a split in the upper (subcorneal or granular) epidermis, whereas vulgaris shows a deeper suprabasal split with a tombstone row of basal cells.
What is Senear-Usher syndrome?
Pemphigus erythematosus — pemphigus foliaceus with lupus erythematosus-like malar rash and mixed immunofluorescence showing intercellular plus basement-membrane-zone staining, sometimes with antinuclear antibodies.
How is the activity of pemphigus foliaceus monitored?
Clinically with lesion counts, and immunologically with ELISA anti-desmoglein 1 antibody titres, which generally parallel disease activity and relapse risk.