NTZ2TTY

Treatment tested

• Methylprednisolone

  Glucocorticoid receptor agonist

• Natalizumab

  Integrin alpha-4/beta-1 inhibitor|Integrin alpha-4/beta-7 inhibitor

• fingolimob (FTY)

Placebo or sham

• Placebo

Other measures (5)

Inclusion Criteria: * Relapsing-Remitting Multiple Sclerosis (Mc Donald's 2010 criteria) * EDSS\<6.0 * At least18 natalizumab infusions * Planned switch from natalizumab to fingolimod * Aged between 18 and 65 * Patients must have received high dose IV methylprednisolone during the 5 previous years Exclusion Criteria: * Progressive MS * Uncontrolled MS with natalizumab (existence of a relapse during the previous 12 months or existence of a gadolinium enhancing lesion on a MRI performed during the last 12 months) * SEP de forme progressive * Contra-indication to the use of high dose oral methylprednisolone * Marked cognitive impairment altering protocole understanding * Switch from natalizumab to a disease modifying treatment different from fingolimod * Contra-indication to fingolimod use * Existence of a disease or condition that could alter study completion * Chronic treatment with steroids * Acute treatment with steroids (more than 300mg during the month prior to inclusion) * Contra-indication to gadolinium containing products injection * Pregnancy

Progressive multifocal leukoencephalopathy (PML) is the most feared complication when natalizumab (NTZ) is used in the treatment of relapsing multiple sclerosis (MS). The risk of PML increases after 18 months of treatment. When switching from NTZ to another disease modifying treatment (DMT) in these MS patients with an active disease, there is a high risk of inflammatory reactivation. Nonetheless, a washout period of several weeks is necessary before initiating a new DMT. The primary purpose of this protocol is to investigate the impact of high dose of oral methylprednisolone, given once a month during the washout period between NTZ and Fingolimod (FTY).