TRANSCRANIAL MAGNETIC STIMULATION WITH SI NGLE AND PAIRED STIMULI IN PATIENTS WITH SPINAL-CORD INJURY

Motor evoked potentials (MEP's) are frequently used to assess spinal c ord injuries. We performed MEP's in a healthy control group and in par aparetic patients with paired stimuli and two types of magnetic coils in order to compare the different coils and to study facilitation phen omena. The patient group I consisted of fourteen persons with a spinal cord injury, the patient groupII included patients with a cauda equin a syndrome. For stimulation a circular coil and a double cone coil wer e used. Interstimulus intervals varied between 10 and 60 ms. Recording s were taken from the tibialis anterior muscle. In the healthy control group higher amplitudes were achieved when using the double cone coil ; latencies were equal for both coils. In patient groupI central motor conduction time was prolonged and MEP amplitudes were decreased (tab. 1 and 2). With the double cone coil a MEP could be elicited in 64%, w ith the circular coil in 39% (tab. 4). With paired stimuli an increase of amplitudes (120%) was seen in the control group (fig. 1) whereas i n patient groupI increases of more than 600% were registered (tab. 3). Paired stimuli evoked motor potentials in three of seven paralysed ex tremities (tab. 6). The best interstimulus interval was found to be be tween 30 and 40 ms (tab. 7). In patient group II no significant differ ence was seen between circular coil and double cone coil. This group d id not show relevant facilitation effects with paired stimuli (tab. 5) . We conclude that the double cone coil is superior to the circular co il for the assessment of motor tracts to the legs. Facilitation phenom ena are much more pronounced in patients with spinal cord injuries tha n in healthy controls or in patients with cauda equina syndrome. Using paired stimuli is an effective method to study the function of motor pathways to the legs, especially in patients with spinal cord disorder s.