A biopsy shows separation of epithelial cells ABOVE the basal layer (intraepithelial/suprabasilar blistering). Positive Nikolsky sign. The MOST likely diagnosis is:

Correct answer: C. Pemphigus vulgaris (PV) — suprabasilar acantholysis

• A. Lichen planus shows T-cell infiltrate, liquefaction degeneration of basal cells, and Civatte bodies — not suprabasilar cleavage.
• B. MMP shows SUBEPITHELIAL separation (below the basal layer) — the cleavage plane is opposite to PV. Nikolsky sign may be negative or mildly positive.
• C. Correct. PEMPHIGUS VULGARIS: biopsy shows SUPRABASILAR cleavage (epithelium separates just above the basal cell layer due to destruction of desmosomes by anti-desmoglein antibodies). The basal cells remain attached to the basement membrane like a 'row of tombstones.' Nikolsky sign is POSITIVE (pressure on mucosa causes blister formation).
• D. Erythema multiforme shows full-thickness epidermal necrosis and subepidermal blistering — not suprabasilar acantholysis.