Pemphigus vulgaris — confirming the diagnosis

Correct answer: A. Immunofluorescence

• A. Correct. IMMUNOFLUORESCENCE is the definitive test. DIRECT immunofluorescence on perilesional tissue shows IgG and C3 deposited in a 'fishnet' or 'chicken-wire' pattern between the epithelial cells; INDIRECT immunofluorescence on serum detects circulating anti-desmoglein antibodies, whose titre tracks disease activity.
• B. Excisional biopsy is for small discrete lesions and does not provide the immunologic information needed here.
• C. Brush biopsy samples surface cells only and cannot demonstrate the level of the split or the antibody deposition pattern.
• D. Exfoliative cytology may show acantholytic TZANCK CELLS, which is suggestive, but it is not diagnostic and cannot distinguish pemphigus from viral acantholysis.

Correct answer: C. Mucous membrane pemphigoid

• A. A non-autoimmune ulcerative stomatitis would not reproduce the desquamative gingivitis with positive Nikolsky sign.
• B. Geographic tongue (benign migratory glossitis) presents as migrating erythematous patches with white serpiginous borders on the tongue dorsum only.
• C. Correct. MUCOUS MEMBRANE PEMPHIGOID is the principal differential. Both are autoimmune vesiculobullous diseases producing desquamative gingivitis with a positive Nikolsky sign, and they are separated by the LEVEL OF THE SPLIT on histology (intraepithelial in pemphigus, subepithelial in pemphigoid) and by the immunofluorescence pattern (intercellular fishnet versus linear basement membrane band).
• D. Nicotinic stomatitis is a white, fissured palate with red-dotted inflamed minor salivary gland openings, caused by heat from smoking.

Note: Erosive lichen planus belongs in this differential too — the classic desquamative gingivitis triad is pemphigus vulgaris, mucous membrane pemphigoid and erosive lichen planus.