External validation of the MOG-AR score in pediatric myelin oligodendrocyte glycoprotein antibody-associated disease

Background Predicting the risk of relapse in myelin oligodendrocyte glycoprotein antibody-associated disease is essential for guiding early treatment decisions. A score evaluating onset age, sex, attack phenotype, and treatment received (MOG-AR) has been proposed to identify patients at high relapse risk since disease onset, but has never been validated in a pediatric population. This study aimed to externally validate the MOG-AR score in an exclusively pediatric cohort.Patients and methods We retrospectively identified 139 children with myelin oligodendrocyte glycoprotein antibody-associated disease (age <18 years) within the past decade. The MOG-AR score was calculated and the patients were stratified into four risk grades. Discrimination and calibration were assessed using multiple complementary metrics, and univariable analyses were performed for each score component. Sensitivity analyses included exploratory reclassification using modified MOG-AR grade thresholds and the development of an exploratory phenotype-based model.Results We included 139 children with a median follow-up of 43 months; relapse occurred in 28.8% of patients. Harrell’s concordance index was 0.472 (95% confidence interval, 0.366–0.577), and the time-dependent area under the receiver operating characteristic curve ranged from 0.467 to 0.510 over 1–5 years. Calibration assessment indicated limited variation in predicted probabilities across risk grades. Modified MOG-AR grade thresholds did not improve risk group separation (log-rank p = 0.359) or alter continuous scores or rankings. The exploratory phenotype-based model showed group separation on log-rank testing (p = 0.031) but poor discrimination (C-index, 0.394).Conclusions In this single-center pediatric cohort, the MOG-AR score did not provide clinically useful stratification of first-relapse risk. Limited variability in the age and treatment-related components may have contributed to its limited performance. Further multicenter validation in pediatric cohorts with broader case-mix and treatment patterns is warranted. The exploratory phenotype-based model requires independent prospective validation.