Letter re: Monitoring long-term efficacy of fampridine in gait-impaired patients with multiple sclerosis.

I read the article by Filli et al.1 with great interest. The authors reported that the responsiveness (efficacy) of prolonged-release fampridine for improving walking in multiple sclerosis (MS) increases over time.1 While the underlying mechanism is not known, its understanding might provide important insight for enhancing the efficacy of fampridine.