Motor Response Matters: Lead Placement and Urologic Efficacy Linked in Sacral Neuromodulation

Objectives: This study aimed to characterize the pelvic floor muscles (PFM) motor response provoked during sacral neuromodulation (SNM) lead placement, determining its utility in improving therapy delivery.

Materials and methods: A prospective pilot study (January 2018-September 2021) was performed including patients with overactive bladder or nonobstructive urinary retention-a very homogeneous group without any medical history interfering with bladder function-who underwent SNM. An external pulse generator was connected for three weeks. Success was defined as ≥50% improvement. PFM electromyography was recorded using a multiple array probe. Differences in electrical PFM motor response (peak-to-peak amplitude, area under the curve [AUC] or latency) among different electrical stimulation levels up to 10V (and the clinically relevant intensities up to 3V) and different parts (four sides, three depths) of the pelvic floor were modeled using linear mixed model analysis (LMM).

Results: The study population comprised 26 women (overall success 81%). With increasing improvement in voiding diary data, higher peak-to-peak amplitudes and AUC were seen for up to 10V stimulation intensities (LMM: p value 0.0046 and 0.0043, respectively) and up to 3V stimulation intensities (LMM: p value 0.0261 and 0.0416, respectively). Subanalysis of the different parts of the PFM showed all different sides (first corrected p value < 0.0125) and depths (first corrected p value < 0.0167) presented with statistically significant differences in favor of those with higher percentage improvement for the 10V and 3V analyses, with only two exceptions: peak-to-peak amplitude at the posterior layer at the clinically relevant stimulation intensities (LMM: p value: 0.0752) and AUC at the posterior layer for the stimulation intensities on 10V (LMM: p value: 0.0557). No statistically significant differences were found for the overall mean peak-to-peak amplitude and AUC based on dichotomous outcome (responders vs nonresponders).

Conclusions: Intraoperative PFM electromyography obtained during lead placement aids in more accurate targeting of the lead to the nerve. To our knowledge, this is the first study to correlate tined lead placement based on electrodiagnostic testing and outcome in SNM. It has been proved to be a reliable measurement tool, serving as a physiological biomarker of treatment response during the test phase. A strong motor response can make the surgeon confident that the correct position of the lead has been established for maximal benefit.