Frequency and risk factors of rebound after fingolimod discontinuation – A retrospective study

Background: Fingolimod (FTY) rebound, a phenomenon of unexpectedly severe disease activity following FTY discontinuation, has been reported to occur in 5–43 % of patients. Only a few larger cohorts have been analyzed. We aimed to determine the frequency and risk factors of FTY rebound in our hospital district in Southern Finland with a population of 1.7 million. Methods: We searched the Finnish MS-register for patients who were previous or current users of FTY for at least 6 months by November 2020. We assessed medical records and collected basic demographic data for the whole cohort. Criteria for a rebound were: (i) the most severe relapse in patient's history and an increase of at least 2 EDSS points during the relapse occurring within 6 months from FTY cessation, or (ii) more than one relapse within 6 months after FTY discontinuation, this being the highest relapse rate observed during the patient's lifetime. Results: Among 3496 MS patients, we found 331 patients ever starting FTY and 283 of them had used FTY for at least 6 months. Among these 283 patients we discovered a total of 114 discontinuation events in 110 patients. Of the discontinuations, 32 (28 %) were followed by a relapse: 20 (17.5 %) were ordinary relapses not fulfilling rebound criteria, and 12 (10.5 %) were rebounds. The median time to an ordinary relapse and rebound were similar: 8.5 weeks (range 1.3–23) and 9.9 weeks (range 5.9–15.9), respectively. The rebound group was younger at diagnosis (p = 0.034) and had used FTY for a longer time (p = 0.048) before discontinuation compared to the group without a relapse. After discontinuation, rebound group had lower lymphocyte values as compared to both ordinary relapse group (p = 0.027) and no-relapse group (p = 0.006) and neutrophil to lymphocyte ratio (NLR) was increased compared to the no-relapse group (p = 0.019). Conclusion: In this study, 10.5 % of patients experienced a rebound, which is similar to the frequencies (10.3–12.5 %) obtained in other larger studies with >100 discontinuations. Relapses of any severity occurred in 28 % of patients discontinuing FTY, and therefore initiation of subsequent disease modifying therapies should occur promptly after discontinuation. Younger age at diagnosis, longer exposure to FTY and lower lymphocyte count as well as higher NLR after discontinuation were identified as risk factors for a rebound. The differences in blood leukocytes indicate that rebound might be a distinct pathophysiological phenomenon compared to an ordinary relapse.