Exploratory Study to Assess the Effect of Fampridine (BIIB041) on Walking Ability and Balance in Participants With Multiple Sclerosis.

The primary objective of the study is to explore the effect of prolonged-released fampridine 10 mg twice daily in patients with Multiple Sclerosis with walking disability. The change of walking ability will be measured using Multiple Sclerosis Walking Scale-12 (MSWS-12) to further elucidate the clinical relevance of changes over 24 weeks treatment duration. Another purpose of this study is to evaluate the safety and tolerability of prolonged-release fampridine. Approximately 120 patients MS will be randomized over 20 sites worldwide. Duration of patient's participation in the study will be approximately 28 weeks.