The effects of 4-aminopyridine on motor evoked potentials in multiple sclerosis.

In order to study the effects of 4-aminopyridine (4-AP) on impulse conduction in multiple sclerosis (MS), we studied motor-evoked potentials (MEPs) in the upper (U/E) and lower extremities (L/E) of six MS patients with stable spastic paraparesis before and after intravenous administration of 4-AP. As a result, we found a significant increase in mean amplitudes in U/E and L/E (P = 0.008) and a significant decrease in the variability of onset latencies in L/E (P = 0.017) without any significant changes in mean and shortest onset latencies. In four limbs of three patients in whom there were no detectable MEP responses before 4-AP administration, definite responses were elicited after 4-AP administration. 4-AP seems to have its therapeutic effects by improving impulse conductivity in demyelinated nerve fibers or by enhancing central or peripheral synaptic transmission, which thus results in coordinated contractions of more muscle fibers in MS.