Cutaneous nodules as a diagnostic clue in multiple myeloma.

Cutaneous plasmacytomas are monoclonal proliferations of plasma cells which can be classified into primary (with no other concomitant bony or extramedullary disease) or secondary (generally associated with multiple myeloma (MM), extramedullary plasmacytoma, or plasma cell leukemia). Cutaneous plasmacytomas can appear in some patients with MM and, rarely, the skin lesions suppose the first clinical manifestation of the disease. Their development is considered as a poor prognostic sign, associated with a life expectancy of less than 12 months after diagnosis. An unusual case of MM is described, in which the histopathological study of a skin nodule provided invaluable information for diagnosis.