Adenopathy and extensive skin patch overlying a plasmacytoma with unusual histologic findings in a patient with polyneuropathy, organomegaly, endocrinopathy, monoclonal protein and skin changes syndrome and Castleman disease.

A 56-year-old previously healthy man presented to the dermatology clinic with a 2-year history of an expanding, violaceous, infiltrated plaque on the right flank. Biopsy revealed a diffuse dermal vascular proliferation of bland, capillary-sized vessels admixed with conspicuous fibrohistiocytic cells including scattered multinucleated floret cells. Further workup revealed a monoclonal gammopathy, an osteolytic chest wall plasmacytoma underlying the plaque, and regional lymphadenopathy leading to a diagnosis of adenopathy and extensive skin patch overlying a plasmacytoma (AESOP). Biopsy of an enlarged lymph node revealed Castleman disease. The patient subsequently developed polyneuropathy and peripheral edema, which supported an additional diagnosis of polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes (POEMS) syndrome. Herein, we discuss the unique findings of our patient, the potential pathogenesis of AESOP, and the link between these three rare paraneoplastic entities along with review of the literature.