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Most patients with multiple sclerosis (MS) experience walking impairment during the course of their disease. From an MS patient's perspective, walking ability is the most important bodily function.1 Currently, sustained-release oral fampridine (fampridine-SR) is the only drug approved for the symptomatic treatment of walking disability due to MS. Fampridine is a potassium channel blocker that improves the impaired axonal conduction associated with CNS demyelination.2 However, only a subpopulation of MS patients with walking disability respond to fampridine.3 Herein, we prospectively evaluated whether pre-therapy motor-evoked potentials (MEP), reflecting pyramidal demyelination by an increased central motor conduction time (CMCT), are suited as a predictive therapeutic response marker.
This prospective observational study was approved by the local ethics committee. Twenty-five patients with definite MS who were undergoing planned therapy with fampridine-SR for clinical reasons were recruited consecutively from our MS outpatient clinic from July 2012 to August 2013. Written informed consent was obtained from all participants. Five patients dropped out of the study due to adverse effects (n=3) or irregular drug intake (n=2); 20 patients were included for further analysis (see online supplementary table 1 for clinical characteristics).
Fampridine-SR 10 mg was administered to the patients twice daily. A timed 25-foot walk (T25FW, two times per measurement) and a timed 50 m walk were assessed before and 14 (range: 13–14) days after treatment initiation. Fampridine responders were prospectively defined by an improvement of >20% in both timed walks.4 However, as only three (15%) of the patients fulfilled this criterion, a posthoc analysis with an arbitrary response definition lowered to an …