Magnetic Resonance Cholangiopancreatography Severity Predicts Disease Outcomes in Pediatric Primary Sclerosing Cholangitis: A Reliability and Validity Study.

Magnetic resonance cholangiopancreatography (MRCP) has not been assessed as a surrogate biomarker in pediatrics. We aimed to determine the inter-rater reliability, prognostic utility, and construct validity of the modified Majoie endoscopic retrograde cholangiopancreatography classification applied to MRCP in a pediatric primary sclerosing cholangitis (PSC) cohort. This single-center, retrospective, cohort study included children with PSC undergoing diagnostic MRCP between 2008 and 2016. Six variations of the Majoie classification were examined: 1) intrahepatic duct (IHD) score, 2) extrahepatic duct (EHD) score (representing the worst intrahepatic and extrahepatic regions, respectively), 3) sum IHD-EHD score, 4) average IHD score, 5) average EHD score, and 6) sum average IHD-EHD score. Inter-rater reliability was assessed using weighted kappas and intraclass correlation coefficients (ICCs). Ability to predict time to PSC-related complications (ascites, esophageal varices, variceal bleed, liver transplant [LT], or cholangiocarcinoma) (primary outcome) and LT (secondary outcome) was assessed with Harrell's concordance statistic (c-statistic) and univariate/multivariable survival analysis. Construct validity was further assessed with Spearman correlations. Forty-five children were included (67% boys; median, 13.6 years). The inter-rater reliability of MRCP scores was substantial to excellent (kappas/ICCs, 0.78-0.82). The sum IHD-EHD score had the best predictive ability for time to PSC complication and LT (c-statistic, 0.80 and SE, 0.06; and c-statistic, 0.97 and SE, 0.01, respectively). Higher MRCP scores were independently associated with a higher rate of PSC-related complications, even after adjusting for the PSC Mayo risk score (hazard ratio, 1.74; 95% confidence interval, 1.14-2.). MRCP sum scores correlated significantly with METAVIR fibrosis stage, total bilirubin, and platelets (r = 0.42, r = 0.33, r = -0.31, respectively; P < 0.05). Conclusion: An MRCP score incorporating the worst affected intrahepatic and extrahepatic regions is reliable and predicts meaningful outcomes in pediatric PSC. Next steps include prospective validation and responsiveness assessment.