This study has 2 components: a 4-week run-in period during which participants are treated with prolonged-release fampridine and undergo subjective and objective assessments of walking ability, the results of which are used to determine who responded to study treatment, and an observational period, during which treatment responders will continue prolonged-release fampridine treatment. The participants who do not meet the criteria to continue study treatment will be offered the opportunity to continue study participation but will not continue prolonged-release fampridine treatment.
