A patient presents with buccal mucosa that peels on slight manipulation, a burning sensation with spicy food, and generalized desquamative gingivitis with a positive Nikolsky sign. What is the most appropriate differential diagnosis?

Pemphigus vulgaris (PV) is an autoimmune blistering disease characterized by: (1) intraepithelial blister formation due to IgG antibodies against desmoglein 1 and 3 (desmosomes); (2) a positive Nikolsky sign (skin/mucosa separates with slight lateral pressure); (3) desquamative gingivitis; (4) oral erosions and ulcers that peel easily. The positive Nikolsky sign is the key distinguishing feature between PV and MMP. Mucous membrane pemphigoid (MMP) has a negative or weakly positive Nikolsky sign and involves subepithelial blistering. Lichen planus typically presents as white reticular lesions (Wickham's striae) or erosive forms. Aphthous stomatitis presents as discrete round ulcers.