Untreated patients with a nodular bronchiectatic form of Mycobacterium avium complex (MAC) suffer long deterioration in the long run despite their lack of symptoms, a new Korean study shows. This suggests that patients with MAC lung disease should be better monitored to avoid irreversible lung damage. The study, "Natural course of the nodular bronchiectatic form of Mycobacterium Avium complex lung disease: Long-term radiologic change without treatment," appeared in the journal PLOS One. Non-tuberculous mycobacteria (NTM) are opportunistic and environmental pathogens. MAC is the most common NTM species, with the prevalence of NTM infection increasing in recent years from 1.4 to 6.6 per 100,000 people. NTM infections mostly strike people with lung illnesses such as chronic obstructive pulmonary disease (COPD), bronchiectasis, cystic fibrosis, primary ciliary dyskinesia and alpha-1-antitrypsin disease. Individuals with no known lung disease can also be infected with these mycobacteria, in which case MAC infection could also cause bronchiectasis. MAC lung diseases are mainly of two clinical forms: a fibrocavitary form and a nodular bronchiectatic (BE) form. This study focused on the nodular BE form. The BE form usually occurs in middle-aged non-smoking women and tends to progress slowly over time. Most MAC patients start treatment when symptoms are more pronounced. When the infection becomes chronic, patients need ongoing treatment. This study aimed to evaluate long-term radiologic changes in untreated MAC lung disease. Researchers analyzed serial chest computed tomography (CT) scans of patients with slow progressing nodular BE who had gone without treatment for at least four years. Researchers examined patients treated at Seoul's Chung-Ang University Hospital between 2005 and 2012. From the initial group of 104 patients with MAC lung disease, the study included 40 with non-treated nodular BE, with at least four-year interval chest CT scans. Among these patients, 82.5 percent were woman. After four years of follow-up, 15 of these 50 had to undergo treatment. The authors evaluated each lung lobe on five major parenchymal abnormalities. The lung parenchyma is the functional part of the lung, including the alveoli and respiratory bronchioles. The authors observed that 33 patients (82.5%) had increased CT scores for bronchiectasis, 28 patients (70.0%) for cellular bronchiolitis, 24 patients (60.0%) for cavities, 27 patients (67.5%) for consolidation, and 16 patients (40%) for nodules. Furthermore, disease progression was strongly associated with bronchiectasis and cavity features. More importantly, 97.5 percent experienced a significant increase in CT score for all five parenchymal abnormalities during the study follow-up. Only one patient had no change in CT score. The authors recognize that their study has several limitations such as small number of patients and a retrospective design — and that only initial and final CT data were analyzed. "Despite these limitations, this study describes the long-term outcome of untreated MAC lung disease in stationary group," the team wrote. The results of this study showed that in these patients, even "minimal symptoms also lead to radiologic deterioration on chest CT during long-term follow-up period." Because "simple chest PA could not detect bronchiectasis and small cavitary lesion," the authors wrote that "careful CT monitoring with appropriate interval might be beneficial" for patients with minimal symptoms.