Diffuse Large B-Cell Lymphoma With Pulmonary and Gastric Involvement Mimicking Nontuberculous Mycobacterial Lung Disease.

An 81-year-old man was incidentally found to have multiple bilateral pulmonary nodules on chest computed tomography. Bronchoscopy revealed Mycobacterium intracellulare, and partial spontaneous regression of several nodules initially supported a diagnosis of nontuberculous mycobacterial lung disease. However, other nodules showed progressive enlargement during antimicrobial therapy. Surgical lung biopsy revealed diffuse large B-cell lymphoma (DLBCL), and subsequent evaluation demonstrated gastric involvement. The patient achieved complete remission after systemic chemotherapy. This case highlights the diagnostic challenge of pulmonary lymphoma presenting with heterogeneous radiological behaviour and emphasizes the importance of histological confirmation when the clinical course is atypical.