Disseminated pulmonary involvement in multiple myeloma: A rare extramedullary manifestation on CT.

Pulmonary involvement in multiple myeloma (MM) is exceedingly rare and poses a diagnostic challenge due to its overlap with infectious and neoplastic pulmonary diseases. We describe the case of a 61-year-old man with known MM who presented with progressive respiratory symptoms. High-resolution CT (HRCT) revealed randomly distributed pulmonary nodules with interstitial thickening, mimicking granulomatous or metastatic disease. CT-guided biopsy demonstrated monoclonal plasma cell infiltration positive for CD138 and kappa light chain restriction, confirming pulmonary involvement by MM. This case underscores the importance of correlating HRCT findings with histopathology for accurate diagnosis of extramedullary pulmonary myeloma, a rare but clinically significant manifestation.