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

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. 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. 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). 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.