This is a multicenter study conducted in 3 parts. Part A is a double-blind placebo-controlled parallel-group period, and Part B and C are open-label extension periods. The primary objective of the double-blind study (Part A) is to assess the effect of Prolonged-Release Fampridine treatment on walking speed as measured by the T25FW (timed 25 foot walk) in Japanese participants with Multiple Sclerosis. The secondary objective of the double-blind portion of the study is to evaluate the safety and tolerability of prolonged-release Fampridine in this study population. The primary objective of the open-label extension study (Part B) is to evaluate the long-term safety profile of prolonged-release Fampridine. The primary objective of the additional open-label extension (Part C) is to provide participants who complete the study with continued access to prolonged-release fampridine until marketed drug can be used at the applicable site or until sponsor decision to discontinue the study.