At-home use of Natalizumab in multiple sclerosis (MS) patients has been temporarily granted by French security agency of medicines and Health products (ANSM). The main objective of the study is to compare the safety of natalizumab administration at home vs at hospital based on retrospective and prospective data collection. Quality of life, patient perception of at-home natalizumab administration are also evaluated as secondary objectives as well as medico-economic assessment of the method.

Data will be collected for a 12-month retrospective period and a 12-month prospective period.

As part of the Covid-19 pandemic, some neurologists have alerted the French authorities (ANSM: National Medicines Safety Agency) to the interruption of natalizumab treatment by some MS patients. The ANSM has granted temporary home use of natalizumab within the framework of a "at-home hospitalization" (HAD) program. The study purpose is to assess at-home natalizumab administration regarding safety, disease activity, quality of life, patient's perception and costs by comparing outcomes before and after "At Home" natalizumab treatment strategy.

The study consists of two periods of observation: a retrospective one corresponding to the year prior the study entry and a prospective one corresponding to patient follow-up for one year from the date of the patient inclusion. The date of the inclusion corresponds to the natalizumab-infusion conducted at hospital just before infusions hospital at-home started. Retrospective data are collected from medical record and a minimal dataset is needed to enroll the patient regarding MRI activity and safety data (i.e., nature and number of SAE and selected AE of grade 2 the year prior study entry).

The prospective period consists of 10 at-home natalizumab infusions (months 1-5 and 7-11) and 3 at-hospital natalizumab infusions (inclusion, months 6 and 12) according to standard care. In addition to clinical, MRI and safety (SAE and selected AE of grade 2) data collected as part of standard medical care from medical record over all the study period, Quality of life (EQ-5D-5L, MusiQol) and patient's preference (Musicare) questionnaires will be administered at inclusion and months 6 and 12 and clinical global impression of change will be recorded at month 6 and 12. Patients will be asked to notify any adverse events that may occur between each at-home infusion and to record each month his/her healthcare resource consumption in a diary. Patients will be contacted each month after at-home infusion to record safety and healthcare resource consumption data.

For a sub-group of 15 patients qualitative interview will be performed between month 3 and 8 as part of patient preference assessment.

Micro-costing dedicated forms and experts' statements will be used to assess resource utilization associated to natalizumab infusion during each period for medico-analyze purpose.

Inclusion Criteria :

1. Male or female over 18 years old;
2. Patients with Relapsing-remitting MS followed in the neurology service
3. Treated for more than 24 months with natalizumab;
4. Anti-JCV negative status at inclusion;
5. Ability to understand the purpose of the study and provide opposition to use protected health information in accordance with national and local subject privacy regulations.
6. Had available medical records to meet study objectives (i.e., SAE and selected AE of grade 2 from the past 12 infusions of natalizumab performed at the hospital before inclusion)
7. Had a cerebral MRI within the previous 12 months (+/- 6 months) which results are available in the medical record.

Exclusion Criteria :

1. Patient having expressed their opposition to the use of their data;
2. Women who are pregnant or breastfeeding or intending to become pregnant during the study;
3. History of any clinically significant (as determined by the Investigator) cardiac, endocrinologic, hematologic, hepatic, immunologic, metabolic (including diabetes), urologic, pulmonary, neurologic (except for RRMS), dermatologic, psychiatric, renal, or other major disease that would preclude participation in a clinical study, in the opinion of the Investigator.
4. Patient under guardianship or under security measure

All patients with relapsing-remitting MS and treated with natalizumab at hospital will be assessed for eligibility.