Mucous Membrane Pemphigoid — ORE Part 1 MCQ

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HardOral MedicineMucous Membrane PemphigoidORE Part 1

A patient presents with painful erythematous and desquamative gingivae. The gingival epithelium peels away when rubbed gently (positive Nikolsky sign). Biopsy from perilesional mucosa shows a subepithelial split with linear IgG and C3 deposition along the basement membrane on direct immunofluorescence. There is no evidence of cutaneous involvement. What is the most likely diagnosis?

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Correct answer: D — Mucous membrane pemphigoid

The combination of clinical, histological, and immunofluorescence findings uniquely identifies mucous membrane pemphigoid (MMP). The subepithelial split rules out pemphigus vulgaris, which shows intraepithelial acantholysis. Linear IgG and C3 at the basement membrane is characteristic of MMP and distinguishes it from pemphigus (which shows cell-surface deposits). Although bullous pemphigoid shows identical immunofluorescence and histological patterns, the absence of cutaneous involvement with predominant oral mucosal disease indicates MMP. Erosive lichen planus lacks basement membrane IgG/C3 deposition. Linear IgA disease is classically IgA-predominant, not IgG-dominant. The positive Nikolsky sign, while supportive, is present in multiple bullous disorders (sensitivity 46.7%, specificity 96.3% for oral bullous disease); diagnosis rests on immunofluorescence pattern and clinical site of involvement.

Reference: PubMed 22137224 (Ocular and oral mucous membrane pemphigoid, 2012); The Lancet 'Pemphigus and bullous pemphigoid' (1999); PubMed 34995762 (Mucous membrane pemphigoid, 2021), https://pubmed.ncbi.nlm.nih.gov/22137224/