Recognizing Pemphigus Vulgaris in a Low Prevalence Setting: A Journey Through Multiple Diagnoses

Pemphigus vulgaris (PV) is an autoimmune blistering disease that may present predominantly with mucosal involvement and is frequently misdiagnosed as infectious or inflammatory conditions. We describe a 72-year-old Filipino woman with a 3-month history of painful oral and genital ulcerations and subsequent flaccid bullae who was initially diagnosed and treated sequentially for candidiasis, disseminated herpes zoster infection, and Behçet's disease based on International Criteria for Behçet's Disease scoring. Despite multiple antimicrobial therapies, her symptoms progressed. Definitive evaluation revealed intraepidermal acantholysis on histopathology and intercellular IgG and C3 deposition in a characteristic "fishnet" pattern on direct immunofluorescence, with positive desmoglein 1 and 3 antibodies, confirming PV. Prompt initiation of systemic corticosteroids led to rapid clinical improvement. This case underscores how diagnostic anchoring and reliance on classification criteria can delay recognition of autoimmune blistering disease, highlighting the need for early biopsy and direct immunofluorescence in persistent mucocutaneous ulceration.