A Low Body Mass Index Is Associated with Unsuccessful Treatment in Patients with Mycobacterium avium Complex Pulmonary Disease

Background: A low body mass index (BMI) has been reported to be a poor prognostic factor for Mycobacterium avium complex pulmonary disease (MAC-PD). The purpose of this study was to clarify the clinical features of MAC-PD in cases with a low BMI. Methods: This retrospective study analyzed the data of patients diagnosed with MAC-PD at Saga University Hospital between 2008 and 2019. The analyzed patient characteristics included age, gender, BMI, symptoms, laboratory data, chest computed tomography findings, and the treatment courses. We also investigated the factors associated with successful treatment. Results: In total, 144 patients were included in this study. The low-BMI group (BMI < 18.5 kg/m(2)) had a higher incidence of sputum, Mycobacterium intracellurare infection, and cavitary lesions, in addition to lower blood lymphocyte counts, higher neutrophil–lymphocyte ratios, and a lower prognostic nutritional index (PNI) when compared to the preserved-BMI group (BMI ≥ 18.5 kg/m(2)). Sixty-six of the 144 patients (45.8%) received treatment. Hemosputum, acid-fast bacillus sputum smear positivity, low lymphocyte counts, a low PNI, and unsuccessful treatment (48.5% vs. 24.2%, p < 0.05) were found to be associated with a low BMI. Conclusions: A low BMI is associated with cavitary lesions, malnutrition, and unsuccessful treatment in MAC-PD.