A Rare Case of Sarcoidosis presenting as a Lung Mass with Treatment Associated Mycobacterium marinum Infection of the Hand.

Sarcoidosis is a systemic granulomatous disease of unknown etiology, characterized by diverse clinical and radiologic manifestations, most commonly affecting the lungs. We report a rare case of a 60-year-old male with CT findings of a lung mass, initially suspected to be malignant, but diagnosed as pulmonary sarcoidosis. The patient was managed with corticosteroids and methotrexate causing immunosuppression. Four years later, he developed progressive swelling and nodules on his left hand, initially presumed to be sarcoidosis-related. Despite treatment, symptoms worsened, prompting further evaluation. Imaging revealed tenosynovitis, and aspiration confirmed Mycobacterium marinum infection. This case highlights the importance of maintaining a broad differential in sarcoidosis patients, particularly those on immunosuppressive therapy. Clinicians should remain vigilant for both sarcoidosis mimicking other pathologies, and opportunistic infections mimicking sarcoidosis progression. Early recognition and appropriate management, including targeted antimicrobial therapy, are crucial to improving outcomes.