Increased multiple sclerosis disease activity in patients transitioned from fingolimod to dimethyl fumarate: a case series.

Background: Fingolimod is a S1P receptor modulator that prevents activated lymphocyte egress from lymphoid tissues causing lymphopenia, mainly affecting CD4+ T lymphocytes. Withdrawal from fingolimod can be followed by severe disease reactivation, and this coincides with return of autoreactive lymphocytes into circulation. The CD8+ T cytotoxic population returns prior to the regulatory CD4+ T lymphocytes leading to a state of dysregulation, which may contribute to the rebound and severity of clinical relapses. On the other hand, dimethyl fumarate (DMF) preferentially reduces CD8+ T lymphocytes, has the same efficacy as fingolimod, and therefore, was expected to be a suitable oral alternative to reduce the rebound associated with fingolimod withdrawal.

Case Presentation: We present six patients with relapsing-remitting MS who developed an unexpected increase in disease activity after transitioning from fingolimod to DMF. All patients were clinically and radiologically stable on fingolimod for at least 1 year. The switch in therapy was due to significantly low CD4+ T lymphocyte count ≤65 cells/ul (normal range 490-1740 cells/ul), after discussing the results with the patients and the potential risk for opportunistic infections including cryptococcal infections. DMF was introduced following a washout period of 5 to 11 weeks to allow reconstitution of the immune system and for the absolute lymphocyte count to reach ≥500 cells/ul. Every patient who experienced a relapse had several enhancing lesions in the brain and/or spinal cord between 12 to 23 weeks after cessation of fingolimod and 1 to 18 weeks after starting DMF. All relapses were treated with intravenous methylprednisolone with good clinical responses.

Conclusion: The anticipated beneficial response of DMF treatment to mitigate rebound after fingolimod therapy cessation was not observed. Our patients experienced rebound disease despite being on treatment with DMF. Additional studies are necessary to understand which treatments are most effective to transition to after discontinuing fingolimod.