Pilot Study to Assess Disease Stability in a Natalizumab to Dimethyl Fumarate Crossover Design

This is an investigator initiated, single site, open-label, single arm observational study examining the initial efficacy and tolerability of dimethyl fumarate in a real world clinical setting for patients with a relapsing form of Multiple Sclerosis (MS) when crossed over from natalizumab therapy. The decision to cross over from natalizumab to DMF will be made by the patient and the prescribing physician and must precede enrollment in the study. MS disease status and history will be gathered from the patient's medical records. Patients will be followed for the first 24 weeks of their transition from natalizumab. Assessments will be performed at Baseline and every 4 weeks thereafter for 24 weeks. These assessments may include: * Expanded Disability Status Scale (EDSS) * Relapse Assessment * Patient Reported Outcomes (PRO) including quality of life, fatigue, and cognition outcome measures * Magnetic Resonance Imaging (MRI) * Laboratory testing Study drop outs due to DMF intolerability or other etiologies will be encouraged to complete the trial even if placed on alternative therapies.