A 15-year-old girl presents with generalized desquamative gingivitis with erythema, sloughing epithelium, and a positive Nikolsky sign. What is the MOST likely diagnosis?

Correct answer: A. Pemphigus vulgaris

• A. CORRECT. DESQUAMATIVE GINGIVITIS with a positive Nikolsky sign is a clinical presentation, not a diagnosis — its differential is PEMPHIGUS VULGARIS, mucous membrane pemphigoid, and erosive lichen planus. Pemphigus vulgaris is an autoimmune disease with IgG autoantibodies against DESMOGLEIN 3 (and 1), producing INTRAEPITHELIAL (suprabasilar) acantholysis with the classic 'row of tombstones' basal layer. The oral lesions typically precede skin lesions by months, so the dentist often makes the first diagnosis.
• B. Plaque-induced gingivitis does not produce epithelial sloughing or a positive Nikolsky sign, and it improves with plaque control.
• C. Puberty gingivitis is an exaggerated inflammatory response to plaque with enlargement, not desquamation.
• D. NUG shows punched-out, necrotic interdental papillae with a pseudomembrane, fetid odor, and pain — a different clinical picture.

Note: Split level matters: pemphigus = INTRAepithelial (suprabasilar). Pemphigoid = SUBepithelial (full-thickness separation). Direct immunofluorescence distinguishes them.