Uncommon Presentation of Multiple Myeloma: Pleural Effusion and Extensive Extramedullary Involvement.

A 60-year-old female presented with abdominal pain, weight loss, and fatigue. Imaging revealed a pancreatic mass, bilateral pleural effusion, ascites, and lytic bony lesions. Investigations confirmed multiple myeloma with lambda light chain disease. Positron emission tomography-computed tomography (PET-CT) scan demonstrated extensive metabolically active soft tissue masses involving the pancreatic region, retroperitoneum, mediastinum, paravertebral regions, and multiple skeletal lesions with extraosseous soft tissue involvement, along with bilateral pleural effusions with metabolically active pleural and extrapleural deposits. The patient was initiated on a bortezomib, cyclophosphamide, and dexamethasone chemotherapy regimen with therapeutic thoracentesis for pleural effusion management. After two cycles, the patient showed remarkable clinical improvement. A repeat PET-CT scan revealed significant interval regression of soft tissue masses, metabolic activity resolution, and regression of pleural and extrapleural deposits. The extensive skeletal lytic lesions showed morphological stability but regression of associated metabolic activity and extraosseous soft tissue. This case highlights the potential of novel agent-based regimens in achieving exceptional responses in multiple myeloma patients with extensive extramedullary disease (EMD), including uncommon manifestations like pleural effusion. Early recognition and prompt initiation of appropriate therapy are crucial for improving outcomes in such cases.