Appendicular Skeletal Muscle Mass Correlates with Patient-Reported Outcomes and Physical Performance in Patients with Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF), an incurable lung disease of unknown cause, often presents with losses of skeletal muscle mass. IPF requires comprehensive care, but it has not been investigated which skeletal muscle mass index reflects holistic management factors: pulmonary function, patient-reported outcomes (PROs), and physical performance. We compared three representative indices of skeletal muscle mass with holistic management factors in IPF patients. Twenty-seven mild to severe IPF patients (21 male) with the mean age of 76.1 ± 5.9 years were enrolled. The three indices were appendicular skeletal muscle mass index (ASMI), cross-sectional area of pectoralis major (PMCSA), and cross-sectional area of erector spinae muscles (ESMCSA). ASMI is considered as a gold standard for sarcopenia assessment, while PMCSA and ESMCSA are frequently used in IPF. As PROs, we assessed breathlessness with the modified Medical Research Council dyspnea scale (mMRC), symptoms with the chronic obstructive pulmonary disease assessment test (CAT), and health-related quality of life with St. George's Respiratory Questionnaire (SGRQ). For physical performance, peripheral muscle strength and 6-min walk distance (6MWD) were investigated. In this cross-sectional study, ASMI showed the greatest number of significantly correlated indices, such as pulmonary function, peripheral muscle strength, 6MWD, mMRC, and SGRQ. PMCSA showed the next greatest number of correlations, with peripheral muscle strength, 6MWD, and mMRC, whereas ESMCSA showed no significant correlations with any index. Thus, ASMI correlated with both PROs and physical performance, and PMCSA correlated mainly with physical performance. In conclusion, assessing ASMI is helpful for the comprehensive care of patients with IPF.