The effect of timing of high-efficacy therapy on processing speed performance in multiple sclerosis.

BACKGROUND: The potential influence of the timing of high-efficacy disease-modifying therapies (heDMTs) on processing speed (PS) performance is critically lacking in current literature. OBJECTIVE: To assess the extent to which early commencement of heDMTs would be associated with a better PS evolution as compared to moderate efficacy disease-modifying therapies (meDMTs) and delayed commencement of heDMTs. METHODS: In this ongoing prospective longitudinal study, the 695 MS patients that have received a PS evaluation at 12-month of follow-up measured by the iPad®-based Processing Speed Test (PST) were retained for the analysis. All patients who had ever been prescribed a high efficacy disease-modifying therapy (heDMT) were classified in tertiles according to the proportion of their disease duration that had been on heDMTs. Based on these tertiles and the time to the first heDMT from the disease onset, patients were divided into the early heDMT group and the delayed heDMT group. Between-group differences in mean PST standardized (Z-score) change from baseline were analyzed using a linear mixed model. RESULTS: In the multivariable model, each year of delay in starting a heDMT was associated with increased odds of cognitive worsening at 12-month (OR = 1.0324, 95% CI = 1.014-1.062, p<0.05). MeDMT-treated patients were at a significantly higher risk for cognitive worsening than early heDMT patients (OR= 2.57, 95%CI = 1.02-6.17). Linear mixed model-based adjusted mean change in PST Z-score from baseline was significantly better in those patients with the longest proportion of their disease duration treated with heDMT (highest tertile) compared to the lowest tertile (difference 0.37 [95%CI 0.02-0.92;p=0.036) and medium tertile (difference 0.39 [95%CI 0.06-0.31;p=0.037). CONCLUSION: Early he-DMT-treated patients are at significantly lower risk for cognitive worsening. Early administration of heDMTs is associated with greater cognitive functioning improvements than delayed commencement or meDMTs.