During a 2 month run-in period, 2 MRIs will be performed 6 weeks apart and patients will be stratified based on the presence or absence of 1 or more Gadolinium enhancing lesions on the first MRI (Gd-enhancing lesion yes-no) and will be randomized to one of two dose regimens of IGIV-C or matching placebo. Patients will receive study drug infusions every 4 weeks for 48 weeks for a total of 12 infusions. Patients will be evaluated by MRI every 6 weeks and by clinical assessments every 3 months. A follow-up visit will occur 4 weeks after the last infusion.