Somatosensory evoked potentials following pudendal nerve stimulation as indicators of low sacral root involvement in a postlaminectomy patient.

Somatosensory cortical evoked potential studies (SEPs) following stimulation of the pudendal nerves proved useful in objectively documenting preoperative low sacral root involvement in a 33-year-old postlaminectomy patient, presenting with impending cauda equina syndrome and treated by piriformis muscle release with good clinical results. Preoperative P40(P1) latencies of SEPs were abnormally prolonged (47 msec) and returned to normal values (38 msec) postoperatively. This new noninvasive electrodiagnostic method has been described previously for normal subjects only. Further experience with this method is still needed, especially to elucidate the diagnostic reliability of various SEP parameters.