Reduction in Cognitive Processing Speed Surrounding Multiple Sclerosis Relapse

OBJECTIVE: The purpose of this study was to explore the longitudinal relationship between multiple sclerosis (MS) relapses and information processing efficiency among persons with relapsing–remitting MS. METHODS: We conducted a Swedish nationwide cohort study of persons with incident relapsing–remitting MS (2001–2019). Relapse information and symbol digit modalities test (SDMT) scores were obtained from the Swedish MS Registry. Follow‐up was categorized into 2 periods based on relapse status: “relapse” (90 days pre‐relapse to 730 days post‐relapse, subdivided into 10 periods) and “remission.” Linear mixed models compared SDMT scores during the relapse periods to SDMT scores recorded during remission (reference) with results reported as β‐coefficients and 95% confidence intervals (CIs), adjusted for age, sex, SDMT type (written vs oral), time‐varying, disease‐modifying therapy exposure and sequence of SDMT. RESULTS: Over a mean (SD) follow‐up of 10.7 (4.3) years, 31,529 distinct SDMTs were recorded among 3,877 persons with MS. There was a significant decline in information processing efficiency that lasted from 30 days pre‐relapse up to 550 days post‐relapse, with the largest decline occurring 0 to 30 days post‐relapse (β‐coefficient: −4.00 (95% CI = −4.61 to −3.39), relative to the period of remission. INTERPRETATION: We found evidence of cognitive change up to 1 month prior to relapse onset. The reduction in SDMT lasted 1.5 years and was clinically significant up to 3 months post‐relapse. These results suggest that the effects of a relapse on cognition are longer than previously thought and highlight the importance of reducing relapse rates as a potential means of preserving cognitive function. ANN NEUROL 2022;91:417–423