Natalizumab at a dose of 300 mg intravenous (i.v.) infusion each month will be given as standard of care for at least 9 months prior to patient being enrolled in the study. One day after the last infusion of natalizumab the patient will start conversion paradigms to Glatiramer Acetate (GA). GA will be administered daily at a subcutaneous (s.c.) dose of 20 mg. On day 1, 2 months after the patient has been on GA therapy, patient will be randomized to be treated with methylprednisolone or methylprednisolone placebo at an oral dose of 192 mg/day po for 5 consecutive days per month for the duration of the study.