Effects of 4-aminopyridine in patients with multiple sclerosis.

4-Aminopyridine (4-AP) was administered to two groups of patients with multiple sclerosis (MS). The first group consisted of 5 patients with labile visual symptoms, 2 of whom had arcuate scotomata. 4-AP improved visual performance of most patients in this group and reduced the size of scotomata. The second group consisted of 5 patients with the spinal form of MS who were in a stable state; in this group 4-AP had little effect clinically or on tests of visual function.