A patient presents with generalized erythematous, painful gingiva with areas of peeling mucosa (desquamation). Nikolsky's sign is positive. What is the differential diagnosis that should be EXCLUDED?

Correct answer: C. Aphthous stomatitis (recurrent aphthous ulcers)

• A. Mucous membrane pemphigoid (MMP) is the most common cause of desquamative gingivitis. It targets hemidesmosomes, causing subepithelial blistering and desquamation.
• B. Pemphigus vulgaris causes intraepithelial blistering and desquamation of the gingiva. Positive Nikolsky's sign is characteristic.
• C. CORRECT. Aphthous ulcers are the ONLY condition in this list that does NOT cause desquamative gingivitis. Aphthous stomatitis affects NON-KERATINIZED, movable mucosa (buccal mucosa, floor of mouth, soft palate) and does NOT involve the attached gingiva as a primary site. Positive Nikolsky's sign, gingival involvement, and desquamation point to autoimmune vesiculobullous diseases — MMP, PV, or LP. Aphthous ulcers are excluded from the differential for desquamative gingivitis.
• D. Erosive lichen planus frequently presents as desquamative gingivitis with atrophic, painful gingiva.