Skeletal muscle fatty deposition in young and middle-aged adults with metabolic dysfunction-associated fatty liver disease: a magnetic resonance proton density fat fraction study.

Background: Metabolic dysfunction-associated fatty liver disease (MAFLD)-a major global health concern-is known to influence skeletal muscle. Therefore, in this study, we investigated whether the changes fat in skeletal muscle are associated with the degree of fatty liver in patients with MAFLD. Methods: We evaluated 398 patients who underwent abdominal magnetic resonance imaging (MRI) between January 2020 and August 2023 in a tertiary university hospital. Using MRI proton density fat fraction (PDFF), two radiologists manually measured the hepatic fat fraction (HFF), psoas major fat fraction (PMFF), paraspinal muscle fat fraction (PAMFF), and subcutaneous adipose tissue thickness (SATT). The severity of hepatic fatty deposition was classified as follows: G0, HFF <5%; G1, 5%≤ HFF <10%; G2, 10%≤ HFF <25%; and G3, HFF ≥25%). Results: PMFF and PAMFF increased in a stepwise manner as the severity of hepatic steatosis increased. There were no significant differences in PMFF or PAMFF between the G2 and G3 groups (P=0.058), while PMFF and PAMFF differed significantly between the other groups (P<0.05). The Pearson analysis showed that HFF was positively correlated with PMFF (r=0.475; P<0.001) and PAMFF (r=0.343; P<0.001). After adjustments were made for the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglyceride (TG), and albumin (ALB), these correlations remained significant (PMFF: r=0.332, P<0.001; PAMFF: r=0.392, P<0.001). PMFF was positively correlated with age (r=0.155; P=0.002), ALT (r=0.169; P=0.003), AST (r=0.186; P=0.001), and blood glucose levels (r=0.177; P=0.003). PAMFF was positively correlated with age (r=0.107; P=0.033), ALT (r=0.118; P=0.040), AST (r=0.169; P=0.004), and blood glucose level (r=0.138; P=0.020) but negatively correlated with ALB level (r=-0.168; P=0.004). SATT was negatively correlated with age (r=-0.301; P=0.000), TG (r=-0.171; P=0.003), and ALB (r=-0.145; P=0.013). HFF was positively correlated with blood glucose level (r=0.144; P=0.015), and blood glucose level partly mediated the relationship between HFF and PAMFF (indirect effect =0.0046; 95 % CI: 0.0004-0.0130). Conclusions: Skeletal muscle fat content is significantly associated with the severity of hepatic steatosis. Accurate and quantitative body composition measurement and degree of hepatic steatosis can be noninvasively performed using PDFF.