Psoas muscle area and paraspinal muscle fat in children and young adults with or without obesity and fatty liver

Background Little is known about the muscle condition in children with obesity. Objectives To investigate the effect of obesity and fatty liver on muscle area and muscle fat in children and young adults. Materials and methods We evaluated consecutive liver fat quantification MRIs in children and young adults between June 2015 and April 2019. We obtained hepatic fat and paraspinal muscle fat at mid L2 from the fat map, psoas muscle area (PMA) at mid L3, and z-score of PMA. The patient's age, height and weight at the time of the MRI were recorded. Body mass index (BMI) z-score was also calculated. Spearman correlation and partial correlation analyses were performed. Univariate and multivariate regression analyses were also performed using significant variables. Results A total of 132 patients (97 male) were included with a median age of 13.0 years (interquartile range 11-16 years). The median BMI was 23.7 kg/m2 (interquartile range 21.2-27.7 kg/m2). The weight, BMI, liver fat, and z-score of PMA were all higher in male patients than they were in female patients. The amount of liver fat had no correlation with muscle fat or PMA zscore after adjusting BMI. However, the BMI z-score was positively correlated with the PMA z-score (p = 0.432, p<0.001) even after adjusting for liver fat. On regression analyses, the BMI z-score had linear positive relationship with PMA z-score (β = 0.289, p<0.001) and muscle fat (β = 0.218, p = 0.016). Conclusions Male children and young adults have greater PMA than do female children and young adults. Obesity is associated with higher PMA and paraspinal muscle fat. However, liver fat is not related with the muscle condition in children and young adults.