Cerebral potentials evoked by electrical stimulation of the anal canal.

We describe the procedure with which cortical potential responses are evoked by a stimulation of the anal canal to assess the integrity of its sensory pathways. These potentials were recorded in 66 patients. In 44 patients, a cortical evoked response was obtained with a succession of positive and negative peaks, W shaped (35 cases) or V shaped (nine cases). In seven cases, cortical responses were interpreted differently by two independent observers. In these seven patients, such differences could be explained by an insufficient amplification of the recorded electrical waves recorded on paper (< 10 mm). Fifteen patients gave no cortical response. Eight had a neurologic disease that could explain the lack of response. In the seven others, the absence of response was considered as false negative, but six of these stimulations had been carried out during the first part of the study. There is some evidence that cortical evoked potentials may be obtained after an electrical stimulation of the anal canal, but a training period seems necessary to master the technique and obtain reproducible and recognizable responses.