Motor Function and Growth Outcomes With Early Corticosteroid Initiation in Duchenne Muscular Dystrophy: An Adjusted Cross‐Trial Comparison

Introduction/Aims Corticosteroids improve muscle strength and motor function in Duchenne muscular dystrophy (DMD) and are essential to the standard of care. We aimed to quantify effects of earlier versus later corticosteroid initiation on modern measures of motor function among younger patients for whom timeliness of diagnosis, and thus opportunity for treatment, is variable. Methods We compared patients with DMD aged 4 to < 8 years initiating daily corticosteroids at trial baseline ( n = 114; FOR‐DMD [NCT01603407]) to those not initiating ( n = 42; PolarisDMD [NCT03703882]). Changes in motor function, weight, and height were compared over 12 months between these groups. Baseline prognostic factors were balanced via propensity score weighting. Results Initiating daily corticosteroids was associated with significantly better 12‐month motor function outcomes compared to not initiating, with mean (95% confidence interval) differences of 6.9 (5.5, 8.3) North Star Ambulatory Assessment (NSAA) points, 0.47 (0.36, 0.59) meters/s for 10 m walk/run, and 0.10 (0.08, 0.12) tasks/s for rise from supine, each exceeding minimal clinically important differences. Benefits were consistent across baseline age and motor function subgroups. Weight gain was similar and height gain was lower among corticosteroid‐treated patients by 2.0 (1.3, 2.7) cm. Discussion Given persistent delays between symptom onset and diagnosis in DMD, which contribute to an average diagnosis age of 5 years, these findings underscore the importance of earlier diagnosis to allow time for informed discussions about corticosteroids and to optimize meaningful functional benefits during early developmental years.