The primary goal of this research is to study the prevalence of the wearing-off effect and possible risk factors for wearing-off symptoms in patients with multiple sclerosis using ocrelizumab with the use of questionnaires. Furthermore, the goal is to study whether patients receiving extended dosing of ocrelizumab experience more wearing-off symptoms or adverse events in general. Finally, we would like to extend knowledge on wearing-off symptoms in general.

Ocrelizumab is a monoclonal antibody very effective for the treatment of relapsing-remitting multiple sclerosis and primary progressive multiple sclerosis. Ocrelizumab is usually administered intravenous every six months. Natalizumab is another type of treatment used for relapsing-remitting multiple sclerosis and is administered every four weeks. Often patients report MS-related symptoms just prior to their next infusion such as fatigue, coordination problems or motor problems, the so-called wearing-off phenomenon. The exact etiology of this phenomenon remains unknown. Although not studied before, patients do report similar symptoms when using ocrelizumab. Furthermore, because of the COVID-19 pandemic, some patients receive extended dosing of ocrelizumab based on b-cell count. Whether this can increase wearing-off symptoms is unknown.

The goal of this research is to study the prevalence of wearing-off symptoms and possible risk factors for wearing-off symptoms in patients with multiple sclerosis using ocrelizumab. All patients using ocrelizumab during one year or more that provided written informed consent to participate in the study will be asked to complete three questionnaires before or during their next treatment with ocrelizumab. The questionnaires that will be used are the MSIS-29, the treatment satisfaction questionnaire and a questionnaire about wearing-off symptoms. Exact weight of the participants will be measured. Information about age, gender, date of diagnosis, start date of ocrelizumab, clinical and radiological disease activity, EDSS score, b-cell count and the biomarker neurofilament light will be extracted from the patient files. After two weeks, participants receive two additional digital questionnaires, the MSIS-29 and a follow-up questionnaire about wearing-off symptoms.

Inclusion Criteria:

• 18 years or older
• Diagnosis multiple sclerosis
• Use of ocrelizumab as a treatment for multiple sclerosis for a minimum of one year

Exclusion Criteria:

• Unable to answer questionnaires in Dutch
• Different infusion protocol during the previous ocrelizumab infusion (e.g. 300 mg of ocrelizumab instead of 600 mg).

Patients with multiple sclerosis using ocrelizumab.