Study finds opportunity for using subsensory amplitude settings with SNM for OAB

Sacral neuromodulation using an amplitude setting as low as 50% below sensory level is effective for treating overactive bladder (OAB) in women who are refractory to other therapies, according to results of a prospective study published in Neurourology and Urodynamics.¹ The findings have implications for advancing the use of this therapeutic modality, said Dean S. Elterman, MD, MSc, FRCSC.

The international study randomized women who had a successful test stimulation to undergo neurostimulator device (InterStim II) implantation with an amplitude setting at sensory threshold, 50% of sensory threshold, or 80% of sensory threshold. Forty-three of 46 implanted participants completed the 12-week study.

Analyses of data from 3-day urinary voiding diaries showed that mean reductions from baseline daily urinary incontinence episodes were statistically significant in all groups at 6 and 12 weeks, and similar across the 3 study groups. Health-related quality of life (QOL) measures also improved similarly in all groups.

“Sacral neuromodulation is a safe, effective, well-studied therapy for refractory OAB. The prevailing dogma has been that stimulation should be set at the sensory threshold, the level at which stimulation can be felt, so that the patient will know that the device is ‘working,’” said Elterman, associate professor of surgery (urology) at the University of Toronto in Ontario, Canada. “However, it would be very valuable to know if subsensory stimulation at a level lower than what can be perceived is just as clinically effective because it would mean that patients could benefit from greater comfort and increased device longevity.

“[Although] our study was not designed to compare differences between different sensory thresholds, its findings support the ability to customize therapy for individuals, including with the use of amplitude settings that are lower than what we historically used,” he added. “In the future, larger studies may be able to determine if differences between settings exist.”

Women were recruited for study entry at 15 sites in 5 countries. At baseline, mean number of urinary incontinence episodes per day among the randomized women was 4.8. At the 12-week follow-up, the mean decrease in daily urinary incontinence episodes was –3.0 for the 50% of sensory threshold group, –2.9 for the 80% of sensory threshold group, and –3.6 for the sensory threshold group.

“The reduction in urinary incontinence episodes recorded in our sensory threshold group are similar to those reported in the ROSETTA and InSite trials where the amplitude was set at sensory levels. This comparison validates the findings in our relatively smaller trial,” Elterman said.

Improvements seen in QOL

Patients in the study also completed the International Consultation on Incontinence Modular Questionnaire—Overactive Bladder Symptoms Quality of Life Questionnaire, which assesses health-related QOL, and a patient global impression of improvement questionnaire that simply asked patients to rate the change from baseline in their urinary condition using a scale of 1 (very much better) to 7 (very much worse). The QOL data showed statistically significant improvements in the total questionnaire score and in its 4 subscales (concern, coping, sleep, and social). At 12 weeks, the vast majority of women in the 50%, 80%, and sensory threshold groups reported that their bladder condition was better than at baseline (82.4%, 92.3%, and 92.3%, respectively).

The investigators noted that the ability to use subthreshold amplitude settings has benefits for patients and providers. “With more numerous amplitude options available for the device, including for both rechargeable and recharge-free batteries, an improved understanding of postprocedure programming using subsensory thresholds may allow patients to go longer between battery charging or replacement,” Elterman said.

“In addition, occasionally patients whose device is set at the sensory threshold come in for reprogramming because they feel stimulation outside of the pelvis or in a way that is distracting or unpleasant,” Elterman continued. “Having the stimulation set at a lower but still effective level would improve patient comfort and obviate the need for these reprogramming visits.”

Disclosures: The study was sponsored by Medtronic. Elterman is an investigator and consultant for Medtronic.

Reference

1. Elterman D, Ehlert M, De Ridder D, et al. A prospective, multicenter, international study to explore the effect of three different amplitude settings in female subjects with urinary urge incontinence receiving interstim therapy. Neurourol Urodyn. 2021;40(3):920-928. doi:10.1002/nau.24648