Pemphigus vulgaris and mucous membrane pemphigoid

Correct answer: B. Desmosomes

• A. Hemidesmosomes anchor the BASAL cells to the basement membrane and are the target in MUCOUS MEMBRANE PEMPHIGOID (antibodies to BP180/BP230 and laminin 332), which gives a SUBEPITHELIAL split.
• B. Correct. Pemphigus vulgaris is caused by IgG autoantibodies against DESMOGLEIN 3 (and desmoglein 1), the cadherin proteins of the DESMOSOMES that bind adjacent keratinocytes together. Loss of these connections produces ACANTHOLYSIS and an INTRAEPITHELIAL (suprabasilar) split, leaving the classic 'row of tombstones' basal layer and free-floating Tzanck cells.
• C. Type VII collagen anchoring fibrils are targeted in epidermolysis bullosa acquisita, a different and much rarer condition.
• D. The lamina densa is a basement membrane layer; it is not the primary target in pemphigus.

Note: Memory hook: PemphiGUS = GLUE between cells (desmosomes, intraepithelial split, more serious/potentially fatal). PemphiGOID = GROUND/floor beneath the cells (hemidesmosomes, subepithelial split).

Correct answer: C. Mucous membrane pemphigoid

• A. Lichen planus can rarely involve other sites but does not cause the progressive cicatrising conjunctivitis of MMP.
• B. Pemphigus vulgaris involves skin and mucous membranes but does not characteristically scar the conjunctiva.
• C. Correct. Mucous membrane (cicatricial) pemphigoid has a strong predilection for OCULAR involvement. Subconjunctival scarring produces SYMBLEPHARON (adhesion of the conjunctiva to the globe), entropion, trichiasis, corneal damage and ultimately BLINDNESS. This is why any suspected case is referred urgently to an OPHTHALMOLOGIST.
• D. Aphthous ulceration is confined to non-keratinised oral mucosa. (Behçet syndrome — a distinct condition — does cause uveitis with oral and genital ulceration.)

Note: The word CICATRICIAL means scarring — that is the whole point of the referral. Ophthalmology referral is mandatory even when the eyes appear normal at diagnosis.

Correct answer: B. Incisional (perilesional) biopsy

• A. Brush biopsy collects surface cells only and cannot demonstrate the level of the split or the immunofluorescence pattern.
• B. Correct. An INCISIONAL biopsy taken from PERILESIONAL tissue — intact epithelium immediately adjacent to the lesion — is required, with one specimen in formalin for H&E and a second in Michel's medium for DIRECT IMMUNOFLUORESCENCE, which shows a linear band of IgG and C3 at the basement membrane zone.
• C. Excisional biopsy is for small, discrete lesions that can be removed entirely; it is not appropriate for a diffuse desquamative process.
• D. Culture and sensitivity applies to infection, which this is not.

Note: Do NOT biopsy the ulcer bed itself — the epithelium there has already been lost and the specimen will be non-diagnostic.