Decreasing impact of late relapses on disability worsening in secondary progressive multiple sclerosis

Changes in relapse activity during secondary progressive multiple sclerosis (SPMS) need to be accurately characterized in order to identify patients who might benefit from continuing disease-modifying therapies.

To describe relapse occurrence in patients with SPMS during long-term follow-up and assess its impact on disability worsening.

This retrospective cohort study included 506 patients. We assessed the influence of relapses on time from SPMS onset to an Expanded Disability Status Scale score of 6 (EDSS 6), and on irreversible worsening of EDSS scores across different periods.

The annualized relapse rate (ARR) decreased with patient's age (mean reduction of 43% per decade) and SPMS duration (mean reduction of 46% every 5 years). Post-progression relapses were associated with shorter time from secondary progressive (SP) phase onset to EDSS 6 (hazard ratio (HR) = 1.29, 95% confidence interval (CI) = (1.01, 1.64)). Relapse occurrence during the first 3 years and 3-5 years after SP onset was associated with an increased risk of irreversible EDSS worsening (OR = 3.12 (1.54, 6.31) and 2.04 (1.16, 3.58)). This association was no longer significant after 5 years.

The occurrence of relapses was a marker of short-term disability progression during early SPMS, but did not have decisive impact in later SPMS.