Surface versus needle electrodes in determination of motor conduction time to the external anal sphincter

Patients were referred to our neurophysiological department in order to investigate anorectal function. By the means of magnetic stimulation the total motor conduction can be determined. Only patients with normal latency of the pudendal nerve and normal EMG of the external anal sphincter were examined. Stimulation was carried out above the motor cortex with a MO between 80 and 100%. The recording was carried out in 22 patients with concentric needle electrodes and in the other 18 patients with surface electrodes. The mean latency in the group with surface electrodes was 19.4 ms (SD 1.7), and in the group with needle electrodes 23.4 ms (SD 4). Our results suggest, that in magnetic stimulation above the motor cortex and recording with a concentric needle electrode, the range and the mean was higher than with surface electrodes. In our opinion surface electrodes are preferable to needle electrodes in determining motor conduction time to the external anal sphincter.