Atypical Presentation of Plasmacytoma in a Young Woman

A 45-year-old woman with a history of hypertension, polycystic ovary syndrome, and a family history of triple-negative breast cancer presented to our primary care clinic with an incidental fifth rib mass on a computed tomography (CT) scan of the chest. She reported mild intermittent left-sided chest pain and no constitutional symptoms. One year prior, she had a workup for a breast lesion, which was negative for breast cancer. Two months later, a repeat chest CT and a skeletal bone survey revealed an expansile and destructive left fifth rib lytic lesion concerning multiple myeloma (MM) but no other bony lesions. Serum protein electrophoresis revealed elevated IgA levels, free kappa light chains, and an M spike. A bone marrow biopsy showed an increase in plasma cells but with no clonality. A whole-body positron emission tomography (PET) scan was negative for other bony lesions or other solid tumors. A CT-guided biopsy of the left fifth rib revealed a solitary plasmacytoma (SP). This case study portrays a rare site for an SP and raises clinical awareness for the condition in patients presenting with atypical chest pain. The patient underwent localized radiation therapy, which is the mainstay of treatment for patients with this condition. Patients should also be monitored periodically for progression to MM if diagnosed and treated for an SP.