Methylprednisolone During the Switch Between Natalizumab and Fingolimod

Patients with MS receiving NTZ for at least 18 months and without any disease activity during the previous year will be eligible. Included patients will receive either methylprednisolone (1 gramme, 1 day every 4 weeks for a total of 3 grammes) or undistinguishable capsules of placebo. Every patient will initiate a treatment with FTY 7 weeks after the last NTZ perfusion. Methylprednisolone or placebo will be taken 4, 8 and 12 weeks (W4, W8 and W12) after NTZ discontinuation. A spinal and brain MRI will be performed at baseline (last NTZ perfusion, noted W0) and 16 to 18 weeks after. The last clinical follow-up will be made after 24 weeks.