Hypothesis / aims of study
Sacral neuromodulation (SNM) is a common treatment option for refractory overactive bladder (OAB), non-obstructive urinary retention, and fecal incontinence. During lead placement the lead is inserted near the S3 nerve root and intraoperative lead testing is performed to assess corresponding motor response The objective of this study is to determine if intraoperative electromyography (EMG) and compound muscle action potential responses (CMAP) vs standard motor response affect patient outcomes and outpatient programing.
Study design, materials and methods
This is a retrospective study of patients who have undergone placement of a Medtronic SNM unit at a single institution. Study participants underwent either stage 1 and 2 placement or a combined placement following an office peripheral nerve evaluation from January 2023 to March 2025. We identified patients who underwent placement with either EMG monitoring to identify a CMAP (group 1) or standard motor response testing of the targeted S3 nerve root (group 2). Intraoperative responses of both groups were recorded and compared to their following programing and outcome responses. Pearson’s chi square test and two-tailed T-test were calculated with SPSS.
Results
A total of 77 patients were enrolled, of which 54 had lead placement with EMG monitoring and recorded CMAP responses and 23 individuals had intraoperative motor responses. The mean age for the EMG/CMAP and motor groups was 59.95 and 69.98 years respectively. Both groups had an average BMI of 29.8. There was no statistically significant difference between the different monopolar electrode amplitudes (0-3) between the 2 groups. At the first follow-up visit, the EMG group had a higher number of patients reporting significant improvement in frequency (p = 0.049), retention (p < 0.001), and pain (p < 0.001). Overall, the mean amplitudes for EMG group were lower than non-EMG group (0.84 vs 1.13, p-value 0.04). Additionally, the use of EMG resulted in a lower number of patients requiring program and/or amplitude change to help improve frequency (p-value 0.006), urgency (p = 0.0082), urge incontinence (p = 0.013), nocturia (p = 0.0014), and retention (p = 0.0066).
Interpretation of results
Overall, our study indicates that the use of EMG monitoring during lead placement improves patient outcomes at first follow-up visit. When interpreting these results, there are 2 factors that could confound the study results. First, there was a 10-year difference in age between those that underwent EMG monitoring versus those that did not. Second, patients were seen by 3 different physicians of which one exclusively uses EMG, one only uses standard motor response, and a third physician that has used both approaches. Therefore, the lead placement skills of the physician could play a role in the outcomes of the study.