Risk of multiple sclerosis relapses when switching from fingolimod to cell-depleting agents: the role of washout duration

Background: Fingolimod (FTY) induces sequestration of lymphocytes in secondary lymphoid organs and the average lymphocyte recovery following discontinuation takes 1-2 months. It has been hypothesized that the therapeutic effects of subsequent cell-depleting agents may be compromised if initiated before lymphocyte recovery has occurred. Objective: To assess the risk of relapses following FTY discontinuation and the initiation of a B/T cell-depleting agent in relation to washout duration using data from the Italian MS Register. Methods: The risk of relapses was assessed in relation to different washout durations (< 6, 6-11, 12-17 and > / = 18 weeks) in patients starting alemtuzumab, rituximab, ocrelizumab or cladribine following FTY discontinuation. Results: We included 329 patients in the analysis (226F, 103 M; mean age 41 ± 10 years). During the cell-depleting treatment, the incidence rate ratio for a relapse was significantly greater in patients with a washout period of 12-17 and > / = 18 weeks compared to the reference period (< 6 weeks). The risk of a relapse was significantly influenced by the occurrence of relapses during FTY treatment and by washout length, with hazard ratios markedly increasing with the washout duration. Conclusion: The risk of relapses increases with the washout duration when switching from FTY to lymphocyte-depleting agents.