Extensive soft-tissue involvement by plasmablastic myeloma arising from displaced humeral fractures.

A 44-yr-old man with IgG-lambda multiple myeloma reached a complete response after induction chemotherapy and autologous stem cell transplantation and maintenance therapy with interferon α2b and prednisone 4 yr later, he presented an increase in the M-protein plus extramedullary myeloma involvement with sacrum and clivus plasmacytomas. Treatment with bortezomib, cyclophosphamide and dexamethasone plus local radiotherapy was initiated. The patient developed a bilateral humeral pathological fracture. Surgical osteosynthesis of both humeri was performed with no immediate complications. Two months later, he developed a prominent swelling in both deltoid areas with fever and high serum LDH levels. X-ray examination showed a displacement of bone fragments of both humeri. Humerus CT scan showed a bilateral fracture in proximal diaphysis with posterior displacement. A magnetic resonance of right scapular region revealed a very extensive infiltration originated in the humerus. A fine-needle punction showed a diffuse plasmablastic infiltration. This case illustrates an atypical presentation of extramedullary myeloma with extensive soft-tissue involvement, originated at the fractured lytic lesions, which was likely triggered by bone surgery. This direct mechanism of myeloma spread has been observed in experimental myeloma mouse models.