Cytopathologic findings in "POEMS" syndrome associated with Castleman disease

A 34-year-old man with a history of a scorpion bite followed by increasing polyneuropathy and IgG lambda monoclonal gammopathy was referred for fine-needle aspiration of a lytic bone lesion and an enlarged axillary lymph node. The findings in the bone lesion were consistent with a plasmacytoma. The FNA of the lymph node showed a peculiar capillary proliferation in a background of polymorphous mature lymphocytes. Flow cytometric analysis showed a mixed lymphoid population. The lymph node was originally signed out descriptively, but review of the case showed features consistent with Castleman disease. After the pathologic findings and clinical features were discussed with the clinical team, the diagnosis of POEMS syndrome was established. Subsequent surgical excision of the lymph node was diagnosed as hyaline vascular-variant Castleman disease.