The thickness of erector spinae muscles can be easily measured by computed tomography for the assessment of physical activity: An observational study

The loss of muscle mass and changes in muscle composition are important factors for assessing skeletal muscle dysfunction. The cross-sectional area (CSA) of muscle is usually used to assess skeletal muscle function. However, the CSA of skeletal muscle can be difficult for clinicians to measure because a specific 3D image analysis system for computed tomography (CT) scans is needed. Therefore, we conducted a study to develop a new method of easily assessing physical activity, in which the thickness of the erector spinae muscles (ESMT) was measured by CT, and to compare ESMT to the CSA of the erector spinae muscles (ESMCSA) in patients with nontuberculous mycobacteria (NTM) pulmonary infections who underwent surgery after some preoperative examinations, such as laboratory tests, chest CT scans, spirometry, and 6-minute walk tests (6MWT). We retrospectively studied adult patients with NTM pulmonary infections who underwent a lobectomy at Fukujuji Hospital from April 2010 to March 2016. We assessed the correlations between ESMT and different variables, including ESMCSA. Sixty-one patients with NTM pulmonary infections were included. The median ESMT and ESMCSA were 1371 mm(2) (IQR 1178-1784 mm(2)) and 28.5 mm (IQR 25.4-31.7 mm), respectively, and a very strong linear correlation was observed between ESMT and ESMCSA (R = 0.858, P < .001). ESMT and ESMCSA were positively associated with body weight (ESMT: R = 0.540, P < .001, ESMCSA: R = 0.714, P < .001), body mass index (ESMT: R = 0.421, P < .001, ESMCSA: R = 0.560, P < .001), the 6MWT value (ESMT: R = 0.413, P = .040, ESMCSA: R = 0.503, P = .010), vital capacity (ESMT: R = 0.527, P < .001, ESMCSA: R = 0.577, P < .001), and the forced expiratory volume in 1 second (ESMT: R = 0.460, P < .001, ESMCSA: R = 0.532, P < .001). We demonstrated that compared to ESMCSA, ESMT is easily measured by CT and can be a useful parameter for clinically evaluating physical activity. Furthermore, ESMT and ESMCSA were related to physical activity, as measured by the 6MWT and spirometry.