Myelomatous Pleural Effusion Revealing Underlying Plasma Cell Myeloma: An Uncommon Initial Presentation

Myelomatous pleural effusion (MPE), an uncommon manifestation of plasma cell myeloma (PCM), is characterized by proliferation of neoplastic monoclonal plasma cells (PCs). The incidence of MPE in patients of PCM is scarce and often portends an aggressive disease course. We report the case of a 55-year-old male patient who presented with progressive dyspnea for three days along with complaints of nonspecific back pain for three months. The presence of bilateral pleural effusion on chest radiography prompted a clinical suspicion of tuberculosis, leading to pleural fluid analysis. Pleural fluid analysis revealed an exudative effusion with elevated adenosine deaminase levels. Cytomorphology and cell block study of the pleural fluid revealed atypical PCs and plasma blasts. PC lineage and clonality were confirmed by CD138 positivity and kappa light chain restriction. Based on the cytomorphology findings, a diagnosis of MPE was suspected. A monoclonal "M" spike was noted in the serum protein electrophoresis study. Concomitant biochemical investigations revealed hypercalcemia, anemia, and deranged renal function. Subsequent skeletal radiography showed the presence of lytic bone lesions, and bone marrow examination confirmed PCM with 70% PCs. A diagnosis of PCM with MPE was established. Despite repeated counseling, the patient declined treatment and succumbed within one month of diagnosis. This case highlights the diagnostic significance of pleural fluid cytology in conjunction with clinical, radiological, and laboratory findings in identifying atypical presentations of PCM and also substantiates the poor prognosis associated with MPE. It is important to emphasize that early recognition and timely evaluation are crucial for patient management.