FAME - Fampyra Outcome Measures Study: a Study of Different Outcome Measures on the Effect of Fampyra

Subjects will all receive Fampridine-SR in an open label enrichment phase lasting four weeks. Those 40% improvin the most measured by SSST will go onto the intervention. Here randomization in a 1:1 key between Fampridine-SR and placebo will be undertaken. Treatment will be of either Fampridine-SR 10 mg BID or placebo BID for four weeks. Arms will be double blind.