Unusual localizations of plasmacytoma

Multiple myeloma (MM) is a malignant proliferation of plasma cells in the bone marrow, usually producing a monoclonal paraprotein in the serum. Active disease can occur in different ways such as bone hypercalcemia, renal failure, anemia, and osteolytic lesions (CRAB definition of end organ damage) [1]. Uncommonly (<10% of cases), malignant plasma cells can be localized thus producing a single lytic lesion in the bone (solitary plasmacytoma of the bone, SPB) or a single mass involving soft tissues (extramedullary plasmacytoma, EP) in the absence of bone marrow infiltration and systemic disease. SPB usually involves the vertebral column, while EP usually affects the upper respiratory tract [2]. Both conditions tend to evolve to MM, but SPB does so more frequently than EP [3]. Although plasma cell malignancies can involve every skeletal bone, joint pains are not typically myeloma-related and are usually of rheumatologic origin. We here describe an exceptional case of a patient with a previously treated EP of the rhinopharynx, whom after 6 years from diagnosis presented with two unusual recurring articular localizations in his elbow and his patella.