Patient Real-world Clinical, Neurological, Tolerability, and Safety Outcomes for Tecfidera® and Rebif®

Inclusion Criteria: 1. Diagnosis of Clinically Isolated Syndrome (CIS) or a relapse remitting multiple sclerosis (RRMS). 2. Age between 18 - 55 years at the time of index. 3. No evidence of prior disease modifying therapy for MS. 4. Initiated treatment with either Rebif or Tecfidera at the time of index. Patient is considered to have initiated treatment if they took at least one dose. Treatment must have been initiated after the product was approved by the FDA. 5. Availability of a high quality baseline MRI brain scan, which must have occurred between 6 months prior to the index date to 2 weeks after the index date. 6. Availability of clinical data in the patient's record for the full study observation period, as defined in the primary objective. Exclusion Criteria: 1. Pregnant at any time during the study observation period. 2. Presence of pre-existing medical conditions known to be associated with brain pathology (cerebrovascular and neurodegenerative diseases, presence of active alcohol or substance abuse). 3. Patient discontinued initial therapy prior to completing 1 year of treatment due to a reason other than disease activity, tolerability, or safety (e.g. financial, convenience, preference, etc.). 4. Phase III registrational trial patients