Mycobacterium avium-intracellulare pulmonary infection in patients without known predisposing lung disease

We tried to characterize the clinical features and findings on chest high resolution computed tomography (HRCT) of patients with Mycobacterium avium-intracellulare (MAI) pulmonary infection without known predisposing lung disease and with no immunodeficiency. We also aimed to clarify the small airway and alveolar inflammation using bronchoalveolar lavage (BAL) from the affected regions. MAI infection was diagnosed in 53 patients from respiratory samples, including sputum and materials obtained using a fiberoptic bronchoscope. None had a predisposing lung disease or immunodeficiency, as assessed by medical history, routine laboratory data, and previously normal chest radiographs and/or CT scans. The mean age of the 53 patients was 60 +/- 11 years, and 48 were nonsmoking females. They had few respiratory symptoms, although 42% had chronic paranasal sinusitis. Chest HRCT findings showed centrilobular small nodules and ectasia of small bronchi and/or bronchioles located mainly in segment (S) 2, 3, 4, and 5. S1, which is usually affected by pulmonary tuberculosis, was completely free of these opacities. The BAL study revealed that the predominant cells were activated T lymphocytes and neutrophils. The CD4+/CD8+ ratio increased significantly. Bacteriology was negative for other bacteria and fungi. Although our patients did not present with distinct respiratory symptoms, the regions affected by MAI showed a chronic inflammation of mainly neutrophils and activated T lymphocytes. The presence of chronic sinusitis may be merely coincidental. However, its high prevalence and the finding of bronchiectasis in chest HRCT raise the question of whether silent bronchiectasis may be a predisposition.