Sacral nerve stimulation is more efficient in facilitating pelvic floor responses than pudendal nerve stimulation

Introduction: Sacral neuromodulation (SNM) is a third line treatment for pelvic organ dysfunction. Pudendal nerve stimulation (PNS) uses SNM electrode leads in an off-label fashion to also treat pelvic dysfunction. Differences in how stimulation of these two nerve targets activates the urethra and external anal sphincter (EAS) may provide insights into the mechanisms of these therapies. Materials and Methods: During SNM lead implant surgeries, needle electrodes and a high-resolution manometry catheter were used to record EAS electromyography (EMG) and multi-segment urethra pressure, respectively. Intra-operative sacral nerve stimulation (SNS) was performed, and EMG and pressure data were analyzed to examine relationships between the responses and stimulation. Pressure data was then compared to previously collected PNS-evoked responses. Results: Nine participants had data recorded during a SNM lead implant surgery. The applied current threshold to activate the urethra was significantly higher than visual motor threshold (VMT; p = 0.04). The EAS threshold was higher but not significantly different from VMT (p = 0.06). Maximum urethra pressure changes during SNS were not different from PNS driven changes (p = 0.09). Current amplitudes required to elicit maximum changes in urethra pressure were lower for SNS than PNS (p = 0.01) and the maximum change in urethra pressure per mA of applied stimulation was higher for SNS than PNS (p = 0.005). Conclusion: This is the first work to compare muscle recruitment between SNS and PNS in humans. SNS has greater pelvic floor recruitment per step in current than PNS. Typical SNM leads are closer to the nerve target, which may contribute to this effect.