Corticosteroid Treatment of Multiple Sclerosis Relapses is Associated with Lower Disability Worsening over 5 Years.

Corticosteroid treatment of multiple sclerosis (MS) relapses is assumed to improve the speed of relapse recovery, without modifying long-term disability risk. We aimed to re-evaluate this assumption in a large cohort of individuals with MS. Individuals with clinically definite MS and ≥3 Expanded Disability Status Scale (EDSS) measurements over ≥12 months were identified within the international neuroimmunology registry MSBase. Individuals were required to have ≥1 relapse, with complete information on relapse treatment, phenotype and severity for all documented relapses. The primary outcome was disability worsening confirmed over 12 months. The association of the cumulative number of steroid-treated and untreated relapses (as a time-varying exposure) with disability worsening was evaluated with Cox proportional hazards. In total, 3673 individuals met the inclusion criteria (71% female, mean age 38 years, mean disability EDSS step 2); 5809 relapses (4671 treated/1138 untreated) were captured (annualised relapse rate 0.19). Over the study period (total 30 175 person-years), 32.7% reached the outcome of confirmed disability worsening (median survival time 5.2 years). Non-treated relapses were associated with a higher risk of disability worsening (HR 1.72, 95% CI 1.57 to 1.88) than steroid-treated relapses (HR 1.50, 95% CI 1.43 to 1.57). This association was modified by the efficacy of disease-modifying therapy at the time of relapse. Our results suggest that a lack of steroid treatment of MS relapses is associated with a higher risk of future disability worsening. Hence, corticosteroid treatment of MS relapses may impact not only the speed of recovery but also the severity of residual structural damage.