Supplementary Material for: Racial and ethnic differences in timing of diagnosis and clinical services received in Duchenne Muscular Dystrophy

Introduction: Racial/ethnic differences in diagnostic and treatment services have been identified for a range of health conditions and outcomes. The current study aimed to analyze whether there are racial/ethnic differences in the timing of diagnostic testing and treatments for males with Duchenne Muscular Dystrophy (DMD). Methods: Diagnostic and clinical data for male individuals with DMD born during 1990-2010 were analyzed from eight sites (Arizona, Colorado, Georgia, Iowa, Piedmont Region of North Carolina, western New York, South Carolina, Utah) of the Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet). Seven milestones related to diagnosis/treatment experiences were selected as outcomes. Times to each milestone were estimated and compared by four racial/ethnic groups using Kaplan-Meier estimation and Cox proportional hazard models. Times between initial evaluation or diagnostic testing and later milestones were also compared by race/ethnicity. Results: We identified 682 males with definite or probable DMD of whom 61.7% were non-Hispanic White, 20.5% Hispanic, 10.6% other, and 7.2% non-Hispanic Black. Seven milestone events were studied (initial evaluation, first neurology/neuromuscular visit, diagnosis, corticosteroid treatment first offered, corticosteroid treatment started, first electrocardiogram or echocardiogram, and first pulmonary function testing). The first five milestone events occurred at an older age for non-Hispanic Black individuals compared to non-Hispanic White individuals. Time from diagnosis to first offering of corticosteroids and initiation of corticosteroid therapy was later for Hispanic individuals compared to non-Hispanic White individuals. When accounting for timing of initial evaluation/diagnosis, offering of corticosteroids continued to occur later, but first pulmonary testing occurred earlier, among Hispanic individuals compared to non-Hispanic Whites. No significant delays remained for non-Hispanic Black individuals after accounting for later initial evaluation/diagnosis. Conclusion: We described racial/ethnic differences in ages at selected diagnostic and treatment milestones. The most notable differences were significant delays for five of seven milestones in non-Hispanic Black individuals, which appeared to be attributable to later initial evaluation/diagnosis. Findings for Hispanic individuals were less consistent. Efforts to address barriers to early evaluation and diagnosis for non-Hispanic Black children with DMD may promote more timely initiation of recommended disease monitoring and interventions.