<qa>  What is the study of teriflunomide effects on cognitive performance in MS patients overDesign: This is a prospective, observational, single-blinded, longitudinal study of teriflunomide effects on cognitive performance in MS patients over 24 months. Neuropsychological status and 3T MRI will be assessed at baseline, 12 months and 24 months. Vocational status will be assessed every three months via the internet. Statistical analysis will emphasize within-subjects changes in all metrics to maximize statistical power. 