Quantitative Evaluation of Thoracic Skeletal Muscle Mass and Normal/Fibrotic Lung Volumes on CT in Idiopathic Pulmonary Fibrosis Patients: Prognostic Significance

Objective: The primary aim of this study is to evaluate the prognostic significance and impact on mortality of sarcopenia—assessed through thoracic skeletal muscles—and threshold-based quantitative lung volumetric analysis in patients with idiopathic pulmonary fibrosis (IPF). Materials and Methods: Patients who underwent non-contrast thoracic CT between January 2019 and August 2023 at Ankara Bilkent City Hospital and exhibited a usual interstitial pneumonia (UIP) pattern in the lung parenchyma were retrospectively reviewed. A total of 106 IPF patients meeting the inclusion criteria and 106 age- and sex-matched control subjects without any chronic lung disease were included in the study. To assess sarcopenia, the cross-sectional area (PMA) and density (PMD) of the pectoralis muscles were measured from the first axial slice above the aortic arch, while the cross-sectional area (ESA) and density (ESD) of the erector spinae muscles were measured from a single axial slice at the lower margin of the 12th thoracic vertebra. Using an artificial intelligence-based analysis software package (Thoracic VCAR, GE Healthcare), normal and fibrotic lung volumes were quantitatively measured. All CT measurements were compared between the patient and control groups. Results: The mean body mass index (BMI) of the patient group was significantly lower than that of the control group (p < 0.05). Additionally, quantitative lung volume measurements (Normal Attenuation Lung Volume - NALV [L and %], Low Attenuation Lung Volume - LALV [%], High Attenuation Lung Volume - HALV [L and %], total lung volume) and thoracic skeletal muscle measurements (ESA, ESI, PMA, PMI) were significantly lower in the patient group (p < 0.05). Patients were grouped as sarcopenic or non-sarcopenic based on the distribution of their Erector Spinae Index (ESI) and Pectoralis Muscle Index (PMI). According to ESI, sarcopenic patients had significantly lower two-year survival rates, follow-up durations, normal attenuation lung volume (NALV in L and %), total lung volume, FVC (L), and FEV1 (L) compared to non-sarcopenic patients (p < 0.05). However, when classified by PMI, no statistically significant differences were observed between sarcopenic and non-sarcopenic groups in terms of two-year survival rates or quantitative lung volumes (p > 0.05). Conclusion: ESI and NAAV (%) obtained through quantitative CT analysis are significant prognostic indicators for predicting two-year mortality in IPF patients.