Identifying High‐Attenuating and Low‐Attenuating Muscle Using Computerized Tomography and Exploring Its Impact on Physical Function and Muscle Strength in Obese Critically Ill Patients

BACKGROUND: Computed tomography (CT) methods to estimate sarcopenia in obesity do not differentiate high-attenuating from low-attenuating muscle. The primary purpose of this study was to determine agreement between a CT method using general workstation-derived total and high-attenuating psoas muscle cross-sectional area (CSA) and a commercially available segmentation software-derived value. Secondary purpose was to explore the relationship between quantity of high-attenuating muscle to physical functioning in a pilot cohort of obese medical intensive care unit (MICU) patients. METHODS: We conducted a prospective observational cross-sectional study. CT images of obese MICU patients were reconstructed to calculate total psoas muscle, low-attenuating muscle, and high-attenuating muscle within the third lumbar psoas CSA using a CT method and commercial software. We performed blinded outcome measures of CSA, physical function, and muscle strength in 28 patients. RESULTS: Concordance correlation coefficient for identifying total psoas muscle was 0.96 (95% confidence interval: 0.93-0.98, P-value < 0.0001) between CT method and commercial software. There was moderate correlation between modified Medical Research Council muscle strength scores and high-attenuating psoas muscle CSA (r = 0.47, P = 0.01) and lower extremity strength and high-attenuating psoas muscle CSA (r = 0.40, P = 0.04). CONCLUSION: There was strong agreement between our CT method and a commercial software method to identify total psoas muscle CSA in obesity. Greater total high-attenuating psoas CSA moderately correlated with muscle strength. Additional studies using more objective markers of muscle strength validating these findings are needed.