Clinical characteristics of patients with interstitial lung disease complicated by pulmonary Mycobacterium avium complex disease

<bold>Background:</bold> The incidence of pulmonary <italic>Mycobacterium avium</italic> complex disease (MAC disease) is increasing worldwide, but there are few clinical studies on MAC disease complicated by interstitial lung disease (ILD). <bold>Aims:</bold> To investigate the clinical characteristics of ILD patients complicated by MAC disease and imaging features of the disease. <bold>Methods:</bold> We retrospectively studied medical records of 54 ILD patients diagnosed with MAC disease between 2011 and 2021 at our institution. <bold>Results:</bold> The mean age was 74 years with BMI 20.0 kg/㎡, 25 males and 29 females. The most common diagnosis of ILD in the background was UCIP (21 patients), while the imaging classification of MAC disease was nodular-bronchiectatic (NB) type in 17 patients, fibro-cavitary (FC) type in 15 patients and unclassifiable type in 22 patients, which did not fit into either category. Many of the unclassifiable types were difficult to diagnose, as there were no obvious findings suspicious of MAC infection, as in the NB and FC type. In these patients, only findings were consolidations around the interstitial cysts. As high as thirteen of 54 patients were also complicated with chronic pulmonary aspergillosis. Compared to our overall ILD patients, the mean age was 5 years older with 3.1 kg/㎡less BMI, and the proportion of female was higher. <bold>Conclusion:</bold> Most common type of MAC disease in ILD were unclassifiable type, neither NB nor FC type, and difficult to diagnose. UCIP was most common in the background ILD. ILD patients with MAC disease were more likely older, female, and having less BMI compared to overall ILD patients.