The assessment of myopenia and muscle biopsy in pediatric patients with liver disease awaiting liver transplantation—A cross-sectional analysis

Little is known about the skeletal muscle characteristics (fiber type proportion and size, location of nuclei, presence of fat infiltration) in children with liver disease with radiologically determined myopenia (low muscle mass). During liver transplantation (LTx) surgery, biopsies from the rectus abdominis muscle were collected. Muscle fiber types (I, I/IIA, IIA, IIA/X, IIX) and cross-sectional area index (µm/m 2 ) were determined using immunofluorescence staining. Triacylglycerol and phospholipid content of muscle was determined using gas chromatography. Myopenia was defined using study-specific cutoffs (skeletal muscle index <-2 SD) from age-sex-matched healthy control scans. Myopenia was prevalent in 41% of children. Children also had a high prevalence of high muscle adiposity (37%). Children with myopenia were older (8.4 vs. 0.7 y; p <0.001), had smaller total (median 595 vs. 844 µm/m 2 ; p =0.04) and hybrid IIA/X (612±143 vs. 993±341 µm/m 2 ; p =0.04) muscle fiber size index, lower prevalence of type I fibers (53% vs. 64%; p =0.01) and higher prevalence of type IIA/X hybrid fibers (median 7.5% vs. 0%; p =0.04). Children with myopenia also had a higher prevalence of elevated triacylglycerol content (>75 percentile) within the muscle compared to children without myopenia (36% vs. 0%; p =0.009). Percent of muscle fibers with centralized nuclei was not different between groups. In conclusion, children with myopenia experience differences in skeletal muscle biological characteristics when compared to children without myopenia at LTx, and these findings may have implications for dietary and exercise rehabilitation pre-LTx and post-LTx.