Pemphigus Vulgaris Unmasked in a Patient With Behçet's Disease: A Complex Diagnostic Dilemma.

Behçet's disease (BD) is a systemic vasculitis characterized by recurrent painful oral and genital ulcers, uveitis, and skin lesions. Pemphigus vulgaris (PV), on the other hand, is an autoimmune blistering disorder affecting the mucous membranes and skin, characterized by the presence of intraepidermal vesicles. Herein, we present a female in her 40s with a history of BD who presented to the emergency department with worsening oral and vaginal ulcers and extensive bullae of four months onset. A skin biopsy revealed an intraepidermal vesicle with preservation of the basal layer consistent with PV. A complete workup including vasculitides, connective tissue diseases, and human leukocyte antigen (HLA)-B51 was performed, which revealed a positive HLA-B51. She was treated with oral corticosteroids, rituximab, dapsone, and azathioprine. After nine months, she has remained stable. Our case suggests there may be a shared pathway in the pathophysiology of BD and PV, providing valuable insights for treatment decisions.