CT evaluations of erector spinae muscle, emphysema, and airway disease for predicting mortality in COPD

Background: Recent advances in quantitative chest CT have proposed novel indexes of airway disease, emphysema, and extra-pulmonary disorders in COPD. Loss of skeletal muscles is estimated as a reduction in the cross-sectional area of erector spinae muscles (ESMCSA) that is associated with physical inactivity and poor prognosis. This study tested a hypothesis that in clinical practice where physicians predict prognosis by combining pulmonary function, demographics, and CT findings, ESMCSA has greater predictive power than airway disease and emphysema assessments in COPD. Methods: Using data from a prospective observational study at Kyoto University Hospital, ESMCSA was measured on a CT image at the 12th thoracic vertebra. Total airway count (TAC), wall area percent of the segmental airways (WA%), airway tree to lung volume ratio (AWV%) were calculated to evaluate airway disease. Low attenuation volume percent (LAV%) and fractal dimension of low attenuation clusters (fractal D) were calculated to evaluate emphysema. Results: In total, 247 patients with COPD were enrolled from 2006 to 2012. The median follow-up period was 3295 days and 46 died. In multivariate cox proportional hazards models that adjusted for age, sex, body mass index, mMRC dyspnea scale, airflow limitation, and diffusion capacity, ESMCSA was associated with poor prognosis (hazard ratio [95% confidence interval] =1.3 [1.1-1.5] per 3.7mm2 reduction) more strongly than TAC, WA%, AWV%, LAV%, fractal D. Conclusion: The reduced ESMCSA can predict long-term mortality independent of pulmonary function and demographics. Exploring a preventive strategy against antigravity muscle loss might help improve COPD prognosis.