Inclusion Criteria:

• Patients > 50 years old;
• Secondary progressive phenotype for at least 3 years; The secondary progressive phenotype will be defined as progressive deterioration of disability not due to relapse, with an increase of at least 1 EDSS point since the beginning of the progressive phase (or 0.5 EDSS point if EDSS score ≥ 5.5).
• Disease modifying therapy of MS for at least 3 years (interferon, glatiramer acetate, teriflunomide, dimethyl fumarate, cyclophosphamide, azathioprine, methotrexate, mycophenolate mofetil, rituximab, ocrelizumab); Both patients with the same DMT or with successive DMTs during 3 years can be included. It is important to note that patients could have been treated with fingolimod or natalizumab 2 or 3 years before inclusion, but not during the year before inclusion ;
• No evidence of focal inflammatory activity for at least 3 years (no clinical relapse and no gadolinium enhancement on an MRI scan);
• EDSS≥3.

Concomitant medications with Fampridine are allowed throughout the study, provided they have been introduced at least 1 months before inclusion.

Natalizumab and fingolimod during the year before inclusion were excluded because of the risk of recurrence of inflammatory activity or even rebound of inflammatory activity after withdrawal.

Both patients with the same DMT or with successive DMTs during 3 years can be included, as for example, cyclophosphamide is used for 1 or 2 years, sometimes followed by mycophenolate mofetil.

For Rituximab and Ocrelizumab, inclusion in STOP-I-SEP will be at 6 months from the last infusion to take into account the mode of action of these treatments and their specific administration scheme.

Exclusion Criteria:

• Patients treated with mitoxantrone or alemtuzumab, during the previous 3 years before inclusion;
• Patients treated with natalizumab or fingolimod during the year before inclusion;
• Change of disease modifying therapy of MS for less than a year
• Other neurological or systemic disease ;
• Incapacity to understand or sign the consent form ;
• Contraindication to MRI ;
• Pregnancy or breast-feeding ;
• Patient in another clinical trial
• Persons referred to in Articles L. 1121-5 to L. 1121-8 and L. 1122-1-2 of the Public Health Code (eg minors, protected adults, …).