Extramedullary disease (EMD) is an issue for patients with multiple myeloma (MM), since extramedullary spread of MM is associated with an aggressive course and a poor prognosis. Moreover, the mechanism of EMD development is uncertain. Here, we present extensive extramedullary plasmacytoma occupying the left upper limb of a 66-year-old female patient with MM with an extremely aggressive course and multiple visceral organ involvement without bone marrow infiltration or plasma cell leukemia. EMD of this large size is extremely rare and this case may provide a clue for better understanding of clinical features of EMD in MM.
Keywords: Extramedullary diseases; Multiple myeloma; Tumor heterogeneity.