Muscle Composition and Gas-Transfer Impairment in Idiopathic Pulmonary Fibrosis: A CT-Based Study

Abstract Background Muscle abnormalities and myosteatosis are increasingly recognized as important extrapulmonary features in patients with idiopathic pulmonary fibrosis (IPF). However, their relationship with pulmonary function is not fully understood. This study aimed to investigate the association between CT-derived myosteatosis and pulmonary function, including vital capacity and gas-transfer impairment, in patients with IPF. Methods Eighty-five patients with multidisciplinary diagnoses of IPF were retrospectively evaluated. Myosteatosis Index, a relative muscle-associated adiposity measure, and erector spinae muscle index (ESMI), a muscle-quantity measure, were derived from chest CT. The primary analysis related baseline Myosteatosis Index to diffusing capacity for carbon monoxide (DLCO). Linear models adjusted for age, sex, interstitial lung disease extent, emphysema, body mass index (BMI), and smoking exposure. Baseline ESMI and follow-up forced vital capacity (FVC) were evaluated separately. Exploratory analyses examined both indices against baseline and follow-up DLCO and FVC and compared their associations with BMI. Results Seventy-eight patients were included in the primary analysis. Median age was 68 years and median DLCO was 51.4% predicted. Each 1-standard-deviation higher Myosteatosis Index was associated with 4.99 percentage points lower DLCO after multivariable adjustment (95% confidence interval − 9.30 to − 0.69; p = 0.024). This association remained consistent in sensitivity analyses. Adding the index to a model containing BMI and the other covariates increased explained DLCO variance from 16.1% to 23.0%. Baseline ESMI was not significantly associated with follow-up FVC (n = 80; −0.09 percentage points per 0.01 L/m²; 95% confidence interval − 0.38 to 0.20; p = 0.525). Conclusions Increased CT-derived Myosteatosis Index was independently associated with lower DLCO in patients with IPF, even after adjustment for pulmonary disease extent, BMI, and smoking exposure. These findings suggest that muscle-related body composition changes may provide additional information in the multidimensional assessment of patients with IPF.