Thoracic skeletal muscle quantification: low muscle mass is related with worse prognosis in idiopathic pulmonary fibrosis patients

Abstract

Background: Sarcopenia can contribute to negative outcomes in patients with various lung diseases. However, whether sarcopenia affects prognosis in patients with idiopathic pulmonary fibrosis (IPF) has not been reported. Simple measures of muscle mass, derived from chest computed tomography (CT), are increasingly being used to identify patients with sarcopenia. We hypothesized that skeletal muscle mass could be a predictor of prognosis in IPF patients.

Methods: We retrospectively evaluated 180 patients diagnosed with IPF between January 2010 and December 2015 at a tertiary care hospital in South Korea. We measured thoracic muscle volume by using the cross-sectional area (CSA) of the pectoralis, paraspinal, serratus, and latissimus muscles at the 4th vertebral region (T4_CSA) and the erector spinae muscle (ESM_CSA) at the 12th vertebral region. CT scans at the time of diagnosis were used for analysis and respective CSA were divided by height squared to normalize for stature. Survival times were estimated with the Kaplan-Meier method and compared with the log-rank test. Multivariate Cox proportional hazards models were performed to investigate relationships between clinical parameters and mortality.

Results: Male patients in the lowest quartile of T4_CSA divided by height squared (m²) (T4MI) and in the lowest quartile of ESM_CSA divided by height squared (m²) (T12MI) were more likely to have higher Gender-Age-Physiology Index scores (T4MI, 3.3 ± 1.3 vs 4.0 ± 1.6, P = 0.012; T12MI, 3.2 ± 1.3 vs 4.1 ± 1.6, P = 0.002). Male patients in the lowest quartile of T4MI exhibited a significantly lower survival rate (P = 0.035). After multivariate Cox proportional hazards analysis, T4MI was a significant risk factor for all-cause mortality (HR, 0.955; 95% CI, 0.913-0.998; P = 0.041), whereas T12MI was not (HR, 0.980; 95% CI, 0.856-1.121; P = 0.766).

Conclusions: Low skeletal mass normalized for stature at the level of 4th vertebrae which can be acquired by quantifying thoracic skeletal muscle on single-slice axial chest CT, may be a strong risk factor for all-cause mortality in patients with IPF.

Trial registration: The research protocol was approved by the Institutional Review Board of Severance Hospital, South Korea (IRB No.4-2018-0454).

Keywords: Computed tomography; Idiopathic pulmonary fibrosis; Mortality; Sarcopenia; Skeletal muscle.

Fig. 1

Flow diagram of subjects in this study. Abbreviations; IPF, Idiopathic pulmonary fibrosis; ILD, Interstitial lung disease

Fig. 2

a, b: Sample computed tomography (CT) scans used to determine muscle area in idiopathic pulmonary fibrosis case subjects. Chest CT examinations were obtained by using 24-detector CT scanners (Somatom Emotion 16; Siemens Healthcare, Erlangen, Germany). Non-contrast CTs were used in the analysis. Quantitative assessment of the CSA was performed semi-automatically with Aquarius iNtuition Viewer (ver. 4.4.11, TeraRecon Inc., San Mateo, CA, USA) (a) Axial CT image of the 4th thoracic vertebral region. Pectoralis, intercostalis, paraspinals, serratus, and latissimus muscles are in blue. b Axial CT image of the 12th thoracic vertebral region. Erector spinae muscles are in blue

Fig. 3

a Kaplan–Meier survival curves stratified by the cross-sectional area of pectoralis, intercostalis, paraspinals, serratus, and latissimus muscles at the T4 level in male and female patients . The cutoff value corresponds to the lowest quantile of the cross-sectional area of muscle at the T4 level/height² (T4 muscle index, T4MI) (Male: T4MI = 32.53 cm²/m², n = 108/35 respectively / Female: T4MI = 24.25 cm²/m², n = 28 / 9 respectively). b Kaplan–Meier survival curves stratified by the cross-sectional area of the erector spinae muscles at the T12 level in male and female patients. The cutoff value corresponds to the lowest quantile of the cross-sectional area of erector spinae muscle/height² (T12 muscle index, T12MI). (Male: T12MI = 8.67 cm²/m², n = 104/35 respectively / Female: T12MI = 7.13 cm2/m2, n = 28 / 9 respectively)