Mycobacterium interjectum Lung Infection

A 62-year-old male presented with productive cough, weight loss, and night sweats. CXR revealed a right upper lobe cavitary lesion. Evaluation was negative for Mycobacterium tuberculosis, and sputum revealed Mycobacterium avium intracellulare (MAI). Since his clinical course was atypical for MAI, further investigations were pursued which identified Mycobacterium interjectum in lung specimens, a very rarely described etiology of pulmonary disease. Appropriate therapy with rifampin, intravenous amikacin, trimethoprim/sulfamethoxazole (TMP/SMX), and ethambutol resulted in clinical and radiographic improvement. This is the third case described over a period of 20 years of destructive lung disease in an immunocompetent adult due to M. interjectum. 1. Introduction Various species of Mycobacterium lead to human lung disease. M. tuberculosis has historically been the most common mycobacterial pulmonary pathogen, but numerous nontuberculous mycobacteria (NTM) are increasingly identified as a cause of pulmonary infections. 2. Case Description A 64-year-old male presented to his local physician with drenching night sweats, sixteen-pound unintentional weight loss, and cough productive of dark green sputum for two months. Pertinent negatives included the absence of fever, hemoptysis or dyspnea. Initial chest X-ray (CXR) (Figure 1) demonstrated a right upper lobe cavitary lesion. A 10-day course of ciprofloxacin was provided for a provisional diagnosis of pneumonia without improvement of symptoms. CXR demonstrated progressive cavitation leading to a computed tomography (CT) of the chest (Figure 2) which revealed an 8.6 × 5.9？cm cavity with thick, irregular borders in the right upper lobe with tree-in-bud opacities scattered through the remaining right lung. A sputum sample was negative for M. tuberculosis by RNA amplification analysis, and Quantiferon-Gold test was negative. Sputum samples ultimately grew Mycobacterium avium intracellulare (MAI) prompting treatment with azithromycin, ethambutol, and rifampin which was started almost five months after the onset of symptoms. He presented to our clinic for a second opinion. Further history was notable for current tobacco abuse of 40 pack-year duration and no obvious risk factors for HIV infection. He reported that one of his coworkers was recently placed on isolation for presumed tuberculosis, but this diagnosis was subsequently excluded. He denied any other exposure to tuberculosis or recent travel. Upon presentation, the patient looked well, without respiratory distress, and was afebrile. Physical examination was