External anal sphincter responses after S3 spinal root surface electrical stimulation.

AIMS

The aim of this study is to present the normative data of direct and reflex motor anal sphincter responses, simultaneously evoked by S3 surface electrical stimulation. By this method, it is possible to test the functional integrity of the nervous pathways activated during sacral neuromodulation (SNM).

METHODS

Twenty healthy subjects were studied. Motor-evoked potentials (MEPs) were recorded by concentric needle electrode from external anal sphincter (EAS). Electrical stimulation was applied by means of a bipolar surface electrode over the S3 right or left sacral foramina.

RESULTS

Direct (R1) and reflex responses (R2 and R3) were found at latencies of 6.98, 25.12, and 50.31 msec, respectively. The two first responses were recorded in all the cases; the last response is steadily recorded in 17 out of 20 subjects.

CONCLUSIONS

Our data can serve as reference values for future study in patients with pelvic floor dysfunction. EAS responses following S3 percutaneous electrical stimulation can represent a useful aid in the selection of candidates to SNM.