SummaryBackgroundPrimary malignant pleural effusion has been reported in about 134 cases of multiple myeloma (MM). Associated pleural effusions in cases of MM portend a poor prognosis and identifying them is highly relevant. Reported is the case of a man diagnosed with MM who developed primary myelomatous pleural effusion in the setting of multiple relapses and subsequent mortality within 2 months of the pleural effusion diagnosis.PresentationA 61-year-old African American man was diagnosed with MM in 2011. He received induction therapy of lenalidomide and dexamethasone and an autologous stem cell transplant in 2012. Over the next 5 years, the patient went through alternating periods of remission and relapse that were treated with two rounds of thoracic spine radiation therapy and chemotherapeutic agents. In September 2017, the patient presented with worsening dyspnea and was found to have pleural effusion. Fluid analysis showed plasma cell dyscrasia. Fluid drainage was performed, then the patient was discharged after 1 week which was followed by rapid re-accumulation of fluid and rehospitalization about 10 days after discharge. The patient passed away a few weeks after the second admission.ConclusionPleural effusion carries a differential diagnosis which may include malignancy but is commonly thought to be less specific to multiple myeloma but should still remain in the differential diagnosis. To our knowledge, this is the first case of myelomatous pleural effusion (MPE) that was reported after multiple relapses of MM. MPE is a very rare complication of MM, and its presence is a strong indicator of imminent mortality and need for comfort care in case of multiple relapses. End-stage pleural effusion in MM in the setting of proteasome inhibitor adds more therapeutic and diagnostic challenges.