Difference in Efficacy of Natalizumab Versus Fingolimod for the Treatment of Multiple Sclerosis

Inclusion Criteria: * diagnosis of relapsing-remitting MS in line with McDonald criteria; * patient needing to be treated with FGL or NTZ, either: * Patients who have not responded to complete and well-conducted treatment with beta interferon. The patients should have presented at least one relapse during the course of the previous year while they were receiving treatment, and should present at least 9 hyper-intense lesions within T2 on a cerebral MRI, or at least 1 enhancing lesion following injection of Gadolinium; or * Patients presenting severe and rapidly developing relapsing-remitting multiple sclerosis, defined by 2 debilitating relapses or more during the course of one year, combined with 1 or more high-intensity lesion(s) following injection of Gadolinium on a cerebral MRI, or a significant increase in lesion load within T2 compared to a recent prior MRI. * EDSS score between 0 and 6, not inclusive; * patient who give informed consent, and signed the consent form; * patient available for 12-month follow-up. Exclusion Criteria: * General exclusion criteria: The patient is subject to judicial protection, supervision or guardianship, the patient is pregnant, is about to give birth, or is breast-feeding, or there is an existing medical or major psychiatric condition that, in the investigator's opinion, could represent a risk for the subject or could compromise compliance with the study protocol. * Contraindication to the use of NTZ and FGL in line with the marketing authorisation: for NTZ, the risk of tuberculosis assessed by means of intracutaneous reaction or quantiferon dosage, for FGL, positive VZV serology and an absence of risk factors for bradycardia and heart rate problems, and for both molecules, an absence of biological signs suggesting immunodepression (negative HIV serology, normal CD3, CD4, CD8 and CD19 levels, weight-adjusted dosage of immunoglobulin normal). * prior treatment with FGL or NTZ; * prior treatment with Mitoxantrone or Cyclophosphamide type immunosuppressants during the 5 years before inclusion.