A Case of Plasmablastic Multiple Myeloma With Extramedullary Disease Manifesting as a Myelomatous Pleural Effusion.

Multiple myeloma (MM) is a neoplasm of plasma cell origin characterized by the proliferation of immunoglobulin-producing plasma cells in the bone marrow. Extramedullary disease (EMD) occurs in approximately 10% of patients with MM. Myelomatous pleural effusion (MPE) is a possible manifestation of EMD and has been associated with a poorer prognosis. A 66-year-old female was evaluated after an abnormal serum protein electrophoresis that showed a 2.1 g/dL M-spike in the gamma region, highly suggestive of plasma cell dyscrasia. Imaging subsequently confirmed the bony metastasis. A bone marrow biopsy confirmed plasmablastic MM, and she was started on chemotherapy. She presented three months later with bilateral pleural effusions, with cytology revealing neoplastic plasmacytoid cells. Despite transitioning to dexamethasone, cyclophosphamide, etoposide, and cisplatin (the V-DCEP regimen) due to disease progression, her myeloma remained refractory to treatment, and she expired one month later. MPE in MM is associated with a poor prognosis, with a median overall survival (OS) of 13 months in MPE compared to 37 months in other EMDs. A higher tumor burden and greater multisite extra-medullary lesions are also characteristics of MPE in MM. There is no standard of care for the management of EMD, and salvage regimens such as RVD and V-DCEP are commonly employed. The management of MM with EMD remains a challenge, and more investigation is required before effective treatment regimens may be employed in this setting.