Effect of Tysabri in Patients With Relapsing-Remitting Multiple Sclerosis: A Follow-up Magnetization Transfer Imaging (MTI) Study

The primary objective of this study is to define the effect of Tysabri in patients with relapsing-remitting (RR) multiple sclerosis (MS) over 2 years. The investigators will also explore the extent of remyelination in MS patients treated with Tysabri over 2 years. A secondary objective of this study is to investigate differences in the capacity for remyelination between patients who do or do not respond to Tysabri monotherapy during the same 24 months. A tertiary objective of this study is to monitor Tysabri effect in MS antiphospholipid antibodies positive and MS antiphospholipid antibodies negative patients and to determine perfusion differences according to the antiphospholipid antibodies positivity status.