Paraneoplastic Pemphigus Mimicking Pemphigus Vulgaris Associated With Castleman Disease.

Paraneoplastic pemphigus (PNP) is a rare bullous disease with a polymorphic presentation. Diagnosis can be difficult because it can mimic other bullous diseases, while the underlying neoplasm may be completely asymptomatic. We present the case of a 19-year-old female with a four-year history of exclusively oral bullous lesions, mimicking pemphigus vulgaris, before the diagnosis of a retroperitoneal Castleman disease. While PNP is a severe and sometimes deadly condition, our patient had a mild and long evolution on minimal treatment, with complete resolution after tumor excision. Practitioners should be aware of PNP in young patients presenting with bullous disease and should conduct prompt systemic investigations in refractory or long-evolving cases, even when PNP diagnostic criteria are not fully met.