New-onset nontuberculous mycobacteria pulmonary disease in bronchiectasis: tracking the clinical and radiographic changes

Background: The close association between bronchiectasis and nontuberculous mycobacterial pulmonary disease (NTM-PD) is well-known. However, the clinical impact of subsequent new-onset NTM-PD in bronchiectasis patients has not been elucidated. The aim of this study is to investigate the clinical courses and radiographic changes of patients with bronchiectasis in whom NTM-PD subsequently developed. Methods: A total of 221 patients with bronchiectasis who had participated in a non-NTM bronchiectasis cohort between July 1st 2011 and August 31st 2019 at Seoul National University Hospital were included in this study. The data of patients in whom NTM-PD developed during this observation period were analyzed; specifically, changes in the Bronchiectasis Severity Index (BSI) and lesions on computerized tomography (CT) scan of the chest arising during the observation period. Results: During the observation period, NTM was isolated from 35 patients. A total of 31 patients (14.0%) satisfied the diagnostic criteria of NTM-PD. The median time from enrollment in the cohort to the development of subsequent NTM-PD was 37 months (Interquartile range [IQR], 18-78 months). Mycobacterium avium complex was the most common pathogen (80.6%). Twelve patients underwent antibiotic treatment for NTM-PD with a median interval of 20 months (IQR, 13-30) from the time of NTM-PD diagnosis. When NTM-PD developed, the severity and extent of bronchiectasis, cellular bronchiolitis, and the extent of nodules worsened on CT scans, while BSI did not change. Conclusions: NTM-PD can develop in previously negative bronchiectasis patients. It is associated with worsening radiographic lesions. Active screening of non-NTM bronchiectasis patients for new-onset NTM infection should be considered, especially if radiographic findings worsen. The BSI is not a reliable predictor of new-onset NTM-PD.