Switch to Ofatumumab and Level of Immunoglobulins

This real-life study aims to describe IgG levels after switching from ocrelizumab 600 mg IV every 6 to 8 months in Patients with Multiple Sclerosis (PwMS) to ofatumumab 20 mg SC every month and showing a decreasing level of IgG during treatment by ocrelizumab in real life practice in France over 24 months of follow-up. The primary objective is therefore to determine if the downward trend of IgG observed during ocrelizumab treatment is modified after a switch to ofatumumab, in PwMS treated during at least 18 months of ocrelizumab in real life practice, over 24 months of follow-up.

Inclusion Criteria: 1. Adult patients (≥ 18 years old) who had been treated with ocrelizumab for a relapsing form of Multiple Sclerosis according to the ocrelizumab marketing authorization (MA) treatment regimen for at least 18 months. 2. Patients with a decrease of IgG at a minimum of two consecutive dosages (around six months apart) during ocrelizumab treatment\*. 3. Patients already switched or switching from ocrelizumab to ofatumumab treatment (decision independent from the study\*). 4. Patients agreeing to participate to the study. 5. Able to provide their non-opposition * At the discretion of the investigator, if a benefit for patients is expected based on their experience and depending on patient's characteristics Exclusion Criteria: 1. Patients with ocrelizumab dose spacing \> 8 months in the last 18 months before switch 2. Patient who underwent an immunoglobulin supplementation therapy within 18 months before the switch 3. Ongoing or planned pregnancy