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.