Perineal and Rectal Nerve Recruitment Order Varies During Pudendal Neurostimulator Implant Surgery

Pudendal nerve stimulation (PNS) is an off-label therapy for patients experiencing pelvic pain and voiding dysfunction. The pudendal nerve has two efferent branches to the rectum and perineum. Only the rectal branch is monitored via external anal sphincter electromyography during the implant procedure to help determine the lead position. We examined intraoperative PNS-driven urethral pressures to infer nerve recruitment order and tracked patient reported outcomes.

Patients receiving PNS for pelvic pain and/or urinary symptoms were recruited. During the implant surgery, urethral pressure was measured with a multi-sensor pressure catheter placed in the lower urinary tract. PNS-driven changes in urethral pressure and external anal sphincter (EAS) electromyography were compared to determine the relative perineal and rectal nerve recruitment order. Participants completed pelvic pain, bladder, bowel, and sexual function surveys before and after the surgery. The primary outcome measure was the relative nerve recruitment order during PNS. Secondary outcome measures were the PNS-driven urethral responses and changes in survey symptom scores due to PNS.

Data was collected from thirteen intraoperative sessions. Seven participants had rectal nerve recruitment first, four participants had perineal nerve recruitment first, and two participants had mixed nerve recruitment during intraoperative PNS. The average normalized urethral pressure change was 4.7% at the EAS threshold, 59.2% at twice EAS threshold, and 68.2% at three times the EAS threshold. Urethral pressure changes for each participant often varied between different active PNS electrodes. Participants had significant improvements in pelvic pain and bladder function survey scores with PNS (p < 0.04). There was no relationship between nerve recruitment order and changes in any surveys.

PNS can recruit the perineal nerve before the rectal nerve. Each lead electrode may trigger different urethral response patterns within a participant. This study provided new insights into the effect of PNS on the recruitment of nerves in the pelvis and may help guide future surgical placement of PNS systems.

This study was registered at clinicaltrials.gov (NCT04236596).