Short, not skinny: The distinct sarcopenia phenotype of pediatric primary sclerosing cholangitis‐inflammatory bowel disease

OBJECTIVES: Sarcopenia is prevalent in pediatric liver disease and inflammatory bowel disease (IBD) and predicts adverse outcomes. We aimed to compare sarcopenia prevalence in pediatric primary sclerosing cholangitis (PSC)-colitis versus non-PSC colitis, characterize longitudinal anthropometric trajectories, and examine the association between sarcopenia and liver outcomes. METHODS: This retrospective study compared children with PSC-colitis to matched non-PSC colitis controls. Total psoas muscle area (tPMA) was measured on magnetic resonance enterography. Sarcopenia was defined as tPMA <3rd percentile. Logistic regression examined the PSC-sarcopenia association adjusting for IBD factors. Anthropometric and gamma-glutamyl transferase (GGT) trajectories were analyzed using linear mixed-effects models. RESULTS: Of 85 patients (31 PSC-colitis, 54 non-PSC colitis), sarcopenia prevalence was 42% versus 26%. After adjustment, PSC-colitis patients had nearly fivefold higher odds of sarcopenia (adjusted odds ratio [aOR] 4.81, 95% confidence interval [CI] 1.33-17.36, p = 0.016). However, height-corrected tPMA was similar between groups (p = 0.97), and the PSC-sarcopenia association attenuated when adjusting for height (aOR 3.16, p = 0.085). Sarcopenic PSC-colitis patients demonstrated weight recovery yet persistent height deficits. Sarcopenic non-PSC colitis patients had persistent weight deficits without height impairment. GGT trajectories in PSC-colitis did not differ by sarcopenia status. CONCLUSIONS: Sarcopenia in PSC-colitis may reflect proportionate growth impairment, "short but not skinny," rather than catabolic wasting. This phenotype, characterized by persistent height deficits despite weight recovery and mild colitis, may suggest hepatobiliary or other mechanisms distinct from the gut inflammation-driven sarcopenia in non-PSC colitis and the cachexia of end-stage liver disease.