Neuromodulation and the role of electrodiagnostic techniques

A Deep Analysis of the Pelvic Floor Motor Response in Sacral Neuromodulation Linking It to Outcome

OBJECTIVES

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

MATERIALS AND METHODS

This prospective study (January 2018-September 2021) included patients with overactive bladder (OAB) or nonobstructive urinary retention (NOUR) who underwent unilateral SNM. An external pulse generator was connected for three weeks. Success was defined as ≥50% improvement. Sensory threshold (ST), motor threshold (MT), and their ratio (MT-ST) were analyzed. PFM electromyography was recorded using a multiple array probe. A linear regression model with ST, MT, MT-ST, and mean natural log transformation (peak-to peak-amplitude) vs outcome (percentage improvement) was performed. Differences in electrical PFM motor response amplitude between different electrical stimulation levels (ST ± 0.5 mA) and different parts (four sides, three depths) of the pelvic floor were modeled using linear mixed model analysis (LMM).

RESULTS

The study population comprised 64 women (overall success 80%). Responders presented with significantly lower MT and MT-ST (unpaired t-test: p = 0.0271 and p = 0.0158, respectively). MT and MT-ST proved a significant relationship with percentage improvement (linear regression [lin. Regr.] p = 0.0304, R2 = 0.0745 and lin. Regr. p = 0.0107, R2 = 0.1020, respectively). PFM amplitude showed a significant relationship with percentage improvement for all stimulation amplitudes (ST ± 0.5 mA) (lin. Regr. p < 0.0001, R2 = 0.2560), and subsensory stimulation intensities (lin. Regr. p = 0.0008, R2 = 0.1673). Responders presented with a different evolution in increase in overall peak-to-peak amplitude over increased stimulation intensities (LMM: p = 0.0160), presenting with a significantly higher slope. This was significantly different depending on the percentage improvement for all the different sides and depths, with contralateral superior being the only exception (LMM: p = 0.0071, range: 0.0663-<0.0001).

CONCLUSIONS

A clear correlation was found between therapy efficacy and PFM motor response elicited by unilateral sacral spinal nerve stimulation, linking lead placement and SNM outcome. Responders presented with lower MTs, lower MT-STs, higher compound muscle action potentials, and higher continuous activation of their PFM at subsensory stimulation levels than did nonresponders.

Sensing in Sacral Neuromodulation: A Feasibility Study in Subjects With Urinary Incontinence and Retention

OBJECTIVES

Sacral neuromodulation (SNM) therapy standard of care relies on visual-motor responses and patient-reported sensory responses in deciding optimized lead placement and programming. Automatic detection of stimulation responses could offer a simple, consistent indicator for optimizing SNM. The purpose of this study was to measure and characterize sacral evoked responses (SERs) resulting from sacral nerve stimulation using a commercial, tined SNM lead.

MATERIALS AND METHODS

A custom external research system with stimulation and sensing hardware was connected to the percutaneous extension of an implanted lead during a staged (tined lead) evaluation for SNM. The system collected SER recordings across a range of prespecified stimulation settings (electrode configuration combinations for bipolar stimulation and bipolar sensing) during intraoperative and postoperative sessions in 21 subjects with overactive bladder (OAB) and nonobstructive urinary retention (NOUR). Motor and sensory thresholds were collected during the same sessions.

RESULTS

SERs were detected in all 21 subjects. SER morphology (number of peaks, magnitude, and timing) varied across electrode configurations within and across subjects. Among subjects and electrode configurations tested, recordings contained SERs at motor threshold and/or sensory threshold in 75% to 80% of subjects.

CONCLUSIONS

This study confirmed that implanted SNM leads can be used to directly record SERs elicited by stimulation in subjects with OAB and NOUR. SERs were readily detectable at typical SNM stimulation settings and procedural time points. Using these SERs as possible objective measures of SNM response has the capability to automate patient-specific SNM therapy, potentially providing consistent lead placement, programming, and/or closed-loop therapy.

Sacral Neuromodulation Changes Pelvic Floor Activity in Overactive Bladder Patients-Possible New Insights in Mechanism of Action: A Pilot Study

OBJECTIVES

To evaluate if electrodiagnostic tools can advance the understanding in the effect of sacral neuromodulation (SNM) on pelvic floor activity, more specifically if SNM induces changes in pelvic floor muscle (PFM) contraction.

MATERIALS AND METHODS

Single tertiary center, prospective study (October 2017-May 2018) including patients with overactive bladder syndrome undergoing SNM. Electromyography of the PFM was recorded using the Multiple Array Probe Leiden. The procedure consisted of consecutive stimulations of the lead electrodes with increasing intensity (1-3, 5, 7, 10 V). Recordings were made after electrode placement (T0) and three weeks of SNM (T1). Patients with >50% improvement were defined as responders, others as nonresponders. For the analyses, the highest electrical PFM response (EPFMR), defined as the peak-to-peak amplitude of the muscle response, was identified for each intensity. The sensitivity (intensity where the first EPFMR was registered and the normalized EPFMR as percentage of maximum EPFMR) and the evolution (EMFPR changes over time) were analyzed using linear mixed models.

RESULTS

Fourteen patients were analyzed (nine responders, five nonresponders). For nonresponders, the PFM was significantly less sensitive to stimulation after three weeks (T0: 1.7 V, T1: 2.6 V). The normalized EPFMR was (significantly) lower after three weeks for the ipsilateral side of the PFM for the clinically relevant voltages (1 V: 36%-23%; p = 0.024, 2 V: 56%-29%; p = 0.00001; 3 V: 63%-37%; p = 0.0002). For the nonresponders, the mean EPFMR was significantly lower at 8/12 locations at T1 (T0: 109 μV, T1: 58 μV; mean p = 0.013, range <0.0001-0.0867). For responders, the sensitivity and evolution did not change significantly.

CONCLUSIONS

This is the first study to describe in detail the neurophysiological characteristics of the PFM, and the changes over time upon sacral spinal root stimulation, in responders and nonresponders to SNM. More research is needed to investigate the full potential of EPFMR as a response indicator.

Pelvic Floor Muscle Electromyography as a Guiding Tool During Lead Placement and (Re)Programming in Sacral Neuromodulation Patients: Validity, Reliability, and Feasibility of the Technique

PURPOSE

To assess the validity, reliability, and feasibility of electromyography (EMG) as a tool to measure pelvic floor muscle (PFM) contractions during placement and (re)programming of the tined lead electrodes in sacral neuromodulation (SNM) patients.

MATERIALS AND METHODS

Single tertiary center, prospective study conducted between 2017 and 2019 consisting of three protocols including a total of 75 patients with overactive bladder (wet/dry) or nonobstructive urinary retention. PFM EMG was recorded using the multiple array probe (MAPLe), placed intravaginally. All stimulations (monophasic pulsed square wave, 210 μsec, 14 Hz) were performed using Medtronic's standard SNM stimulation equipment. During lead implantation, all four lead electrodes were stimulated with fixed increasing stimulation intensities (1-2-3-5-7-10 V). During lead electrode (re)programming, five bipolar lead electrode configurations were stimulated twice up to when an electrical PFM motor response (EPFMR), sensory response, and pain response were noted (i.e., the threshold), respectively. Additionally, amplitude and latency of the EPFMRs were determined. Validity, reliability, and feasibility were statistically analyzed using the intraclass correlation coefficient, weighted Cohen's kappa and linear regression, respectively.

RESULTS

Validity: EPFMRs were strongly associated with visually detected PFM motor responses (κ = 0.90). Reliability: EPFMR amplitude (ICC = 0.99) and latency (ICC = 0.93) showed excellent repeatability. Feasibility: linear regression (EPFMR threshold = 0.18 mA + 0.76 * sensory response threshold) showed an increase in the sensory response threshold is associated with a smaller increase in EPFMR threshold, with the EPFMR occurring before or on the sensory response threshold in 83.8% of all stimulations.

CONCLUSIONS

Measuring PFM contractions with EMG during placement and (re)programming of lead electrodes in SNM patients is valid, reliable, and feasible. Therefore, the use of PFM EMG motor responses could be considered as a tool to assist in these procedures.