The impact of low subcutaneous fat in patients with nontuberculous mycobacterial lung disease

Background: Nontuberculous mycobacteria (NTM) are pathogens that cause chronic respiratory disease, even in immunocompetent patients. We hypothesized that low subcutaneous fat is a predisposing factor for NTM lung disease. Methods: Following a retrospective review of medical records from between 2005 and 2012, a total of 148 patients with NTM lung disease and 142 age- and sex-matched controls were enrolled. We evaluated subcutaneous fat using chest computed tomography (CT) scans at the midpole level of the left kidney. Results: The median age of the patients was 62 years and 60.8 % were female. Approximately 71 % were classified into a nodular bronchiectatic group. The patient group had significantly less subcutaneous fat than the control group (39.3 vs. 53.0 cm², p = 0.001). Patients with both localized disease (43.5 vs. 53.0 cm², p = 0.042) and extensive disease (35.9 vs. 53.0 cm², p < 0.0001) had less subcutaneous fat compared with the control group. No difference in subcutaneous fat was observed with respect to the increasing bacterial load in sputum (p = 0.246). In 20 patients with prominent disease progression during the follow-up period, no significant difference was observed between subcutaneous fat at the initial diagnosis and that at the follow-up CT (36.2 vs. 42.0 cm², p = 0.47). Conclusion: Our results suggest that lower subcutaneous fat may contribute to host susceptibility to NTM lung disease.