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

Abstract 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.