Cutaneous paraneoplastic pemphigus syndrome associated with undifferentiated uterine sarcoma.

Pemphigus is a group of autoimmune intraepidermal blistering diseases caused by immunoglobulins directed against keratinocyte cell surface components. In this case report, we identify a non-classical paraneoplastic pemphigus (PNP) foliaceous related to an undifferentiated uterine sarcoma. The patient is a 54-year-old Chinese female with a past medical history of arthritis who presented with worsening fatigue in November 2017 and an itchy, blistering, erythematous annular plaque that first appeared on her chest in February 2018. Given high suspicion for primary immunobullous disease despite negative immunofluorescence and lack of subepidermal split on initial biopsy, a repeat biopsy was performed from the right thigh showing positive intraepidermal "net-like" staining for C3 and IgG, but was negative for IgA, IgM, and fibrinogen. IgG antibodies against desmoglein 1 were elevated at 280u (reference range <18), but none resulted against desmoglein 3, consistent with pemphigus foliaceus. This patient's PNP was resistant to treatment with azathioprine, dapsone, mupirocin cream, or betamethasone ointment, but responded to prednisone and rituximab per lymphoma protocol at 375 mg/m