Comparison of chest CT-derived muscle mass and body mass index in assessing disease severity and outcomes in non-cystic fibrosis bronchiectasis.

PURPOSE: While the association of body mass index (BMI) with bronchiectasis is recognized, the role of body muscle mass are not well understood, especially compared to BMI. METHODS: From January 2017 to June 2020, subjects with diagnoses of bronchiectasis, confirmed by chest computed tomography (CT), were enrolled. Muscle mass was quantified using the muscle area of a single slice of CT at the first lumbar vertebrae, corrected by height squared (L1MI). Subjects were categorized into normal and low L1MI groups based on sex-specific criteria. Low BMI was defined as BMI less than 18.5 kg/m2. RESULTS: Among the 218 participants, 16.5% had low L1MI and 17.0% had low BMI. Low L1MI was associated with older age, male, low BMI, smoking, reduced forced vital capacity, and chronic obstructive pulmonary disease. L1MI and BMI were significantly correlated (R = 0.573, p < 0.001). Low L1MI is an independent risk factor of low BMI (odds ratio: 0.83, p = 0.010). Low L1MI was linked to frequent exacerbations (27.8% vs. 7.4%, p = 0.002) but not mortality. Conversely, low BMI significantly impacted mortality (16.2% vs. 6.6%, log-rank p = 0.028) but not exacerbations. Low BMI and low L1MI had positive correlation with the severity of bronchiectasis, as measured by the bronchiectasis severity index (p < 0.001). CONCLUSIONS: L1MI, likely representing the cumulative risks of bronchiectasis, might be a surrogate of exacerbation as compared with BMI. L1MI determined by routine chest CT might help with early intervention of low body muscle mass.