Association Between Liver and Muscle Fat Fractions: A Study Using the Proton Density Fat Fraction MRI

<b>Aims/Background</b> Metabolic dysfunction-associated steatotic liver disease (MASLD) is a common condition linked to insulin resistance and metabolic syndrome, potentially leading to liver fibrosis. Myosteatosis shares common pathophysiological pathways with MASLD. This study aims to evaluate the relationship between psoas and paraspinal muscle fat content and liver fat content, and compare the muscle fat content in patients with and without fatty liver. <b>Methods</b> Patients who underwent T2* Magnetic Resonance Imaging (T2*MRI) between January 2023 and November 2024 in the Bilkent City Hospital, Ankara, Turkey, were included in the study (n = 280). Fat fractions were determined using the Proton Density Fat Fraction (PDFF). The relationship between liver fat fraction and psoas and paraspinal muscle fat fractions was analysed using age- and sex-adjusted regression models. <b>Results</b> Fatty liver was observed more in men than in women (68% vs. 50%, <i>p</i> = 0.003). Psoas and paraspinal muscle fat fractions were significantly higher in patients with versus without fatty liver (<i>p</i> < 0.001). The regression analysis revealed that both psoas (<i>p</i> = 0.002) and paraspinal muscle (<i>p</i> < 0.001) fat fractions had significant non-linear associations with liver fat fraction. The area under the receiver operating characteristic (ROC) curves demonstrated that the discriminative value of psoas and paraspinal muscle fat fractions for fatty liver were comparable (0.715 vs. 0.678, respectively; <i>p</i> = 0.249). Psoas muscle fat fraction of ≥4.5% and paraspinal muscle fat fraction of ≥7% had a sensitivity of 69.3% and 62.0%; specificity of 65.8% and 72.8%; positive predictive value of 74.7% and 76.9%; and negative predictive value of 59.5% and 56.8% for the diagnosis of fatty liver, respectively. <b>Conclusion</b> There is a non-linear and significant relationship between liver fat fraction and psoas and paraspinal muscle fat fractions. The fat fractions of the psoas and paraspinal muscles were significantly higher in patients with fatty liver, and the diagnostic efficacy level for fatty liver was moderate, and the discriminant values of the two were comparable.