A case of Mycobacterium avium-associated hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) due to nontuberculous mycobacteria (NTM) is an uncommon phenotype of NTM pulmonary disease, classically linked to hot tub or pool exposure. We report a steroid-dependent case of HP-type Mycobacterium avium lung disease likely triggered by outdoor water aerosol exposure.

A 79-year-old man with a 16-pack-year smoking history presented with progressive dyspnea on exertion. High-resolution CT showed bilateral peripheral ground-glass opacities, and serum Krebs von den Lungen-6 was markedly elevated. Bronchoalveolar lavage fluid demonstrated lymphocytic predominance with an increased CD4/CD8 ratio, fulfilling criteria for probable HP. Prednisolone induced clinical and radiological improvement; however, repeated attempts at tapering resulted in relapse with new ground-glass opacities in the right middle lobe and rising biomarkers. Although Mycobacterium avium had been isolated from bronchoalveolar lavage culture, the initial absence of respiratory symptoms and radiographic improvement led to observation alone. Given the difficulty tapering corticosteroids and the positive culture, chronic antigen exposure to environmental NTM was suspected. Further environmental assessment identified a long-standing habit of golfing on a riverside course, where ongoing inhalation of water aerosols was deemed the most likely source of antigenic exposure.

Antigen avoidance combined with azithromycin and ethambutol led to sustained clinical and radiological improvement and successful steroid tapering without restrictive ventilatory impairment. This case underscores the importance of routinely sending mycobacterial cultures from bronchoalveolar lavage in suspected HP and of carefully reassessing environmental exposures, even in outdoor settings, as identifying NTM as the causative antigen can substantially modify management.