Spontaneous resolution of a lung mass due to infection with Mycobacterium terrae.

A 61-year-old smoker had a large right lung mass suggestive of bronchogenic carcinoma. Bronchoscopy showed what appeared to be tumor occlusion of a right middle lobe subsegment. Biopsies were nondiagnostic for malignancy. A scheduled percutaneous needle aspiration biopsy 1 week later was canceled because of a significant reduction in size of the lung mass. Acid-fast bacilli were subsequently found in bronchoscopic specimens, and treatment was started with isoniazid, rifampin, pyrazinamide, and ethambutol. The organism was identified as Mycobacterium terrae. In vitro resistance was noted to isoniazid. The early reduction in size of the mass before antimycobacterial therapy suggested that spontaneous regression may be part of the natural history of pulmonary infection with Mycobacterium terrae.