A80-4-37 Incidental Plasmacytoma: An Unusual Presentation of Multiple Myeloma

Plasmacytomas are a form of plasma cell malignancy which can occur as isolated lesions or as part of systemic multiple myeloma. We present a case of a patient whose evaluation for an incidentally found lung mass led to the diagnosis of multiple myeloma. A 65-year-old man with no remarkable past medical history presented to the emergency department with two days of fever, cough, and chills. A chest x-ray demonstrated findings suggestive of pneumonia as well as a “smoothly marginated density in the left lung apex.” CT chest further revealed a destructive mass involving the left third rib measuring 7.6 x 4.6 cm; it was difficult to determine from imaging if the mass originated from the lung, pleura, or bone. PET-CT showed significant FDG avidity of the mass (SUVmax 40.2) and FDG-avid left mediastinal and supraclavicular lymph nodes. He subsequently presented to outpatient pulmonary clinic for further evaluation. Given imaging findings, primary lung malignancy or soft tissue sarcoma was initially suspected. He underwent CT-guided biopsy of the mass with pathology showing a kappa light chain-restricted plasmacytoma. Serum studies demonstrated a markedly elevated kappa/lambda ratio of 132. Bone marrow biopsy confirmed a kappa light chain-restricted plasma cell myeloma with 20% plasma cells. On review of previous labs, the patient was noted to have anemia (hemoglobin 11.9 g/dL) previously attributed to iron deficiency anemia as well as hypercalcemia (10.3 mg/dL). Renal function was normal. He was diagnosed with multiple myeloma and started on daratumumab, bortezomib, lenalidomide, and dexamethasone (Dara-VRD), with favorable response to treatment. The presence of plasmacytomas is clinically important to recognize in multiple myeloma as they are predictors of poorer outcomes. The site of origin also carries prognostic implications: paraskeletal plasmacytomas arising from bone marrow are associated with better outcomes than extramedullary plasmacytomas which result from hematogenous spread. In one study, paraskeletal plasmacytomas were found to occur in 17.6% of patients with multiple myeloma, with 40% located in the chest; similarly, extramedullary plasmacytomas were associated with the lungs or pleura in 23% of patients. Altogether, this case underscores the importance of considering plasmacytomas in the differential of a lung mass, particularly if there is osseous involvement.