Transcranial magnetic stimulation study in patients with multiple sclerosis on 4-aminopyridine therapy

4-Aminopyridine (4-AP) - a potassium channel blocking agent is used in the symptomatic treatment of a variety of neurological disorders such as multiple sclerosis, chronic spinal cord injuries, myasthenia gravis, myasthenic syndromes etc. Its action in multiple sclerosis is supposed to be mainly by improvement of the synaptic transmission and of the nerve conduction in demyelinated nerve fibers via prolongation of the repolarization phase of the action potential. The aim of the study is to evaluate the effect of 4-AP intramuscular therapy on different parameters of transcranial magnetic stimulation (TMS) - central motor conduction time (CMCT), amplitudes of motor evoked potentials (MEP) and resting motor threshold (RMT), recorded from upper limbs. A group of 18 patients with definite multiple sclerosis with relapsing remitting form was investigated. TMS was performed before and after 5 days of treatment with 4-AP. Evaluation on expanded disability status scale (EDSS) was performed in the beginning and at the end of the study. The results of the study confirm the therapeutic effect of 4-AP - lowering of the RMT of the motor cortex (p < 0.05), increase of the maximal amplitudes of MEP. Less affected was the CMCT. There was no change of disability assessed by EDSS. The most frequent side effect was local pain at the site of injection.