Sacral Nerve Stimulation at Subsensory Threshold Does Not Compromise Treatment Efficacy Results From a Randomized, Blinded Crossover Study

Background and Objective: Stimulation amplitude used in sacral nerve stimulation (SNS) is at or just above the sensory threshold (ST). This randomized, blinded crossover study aimed to document if stimulation at 75% or 50% of the ST would be as effective as stimulation at the ST for fecal incontinence (FI). Method: FI patients treated with SNS, who were satisfied with current treatment results and had a minimum symptom reduction of 75%, were eligible. Patients were randomized into 3 periods of 4-week stimulation: ST, 75% of the ST, and 50% of the ST. Patients completed a bowel habit diary and questionnaires on bowel functions and patient satisfaction at the study baseline and in each study period. Results: Nineteen patients (18 females) with a mean follow-up of 51.7 +/- 29.9 months were included from January to April 2010. The mean FI episodes per 3 weeks decreased from pre-SNS therapy 33.6 +/- 31.6 to 1.1 +/- 2.2 at the study baseline (P < 0.001). Decreasing the stimulation amplitude to as low as 50% of the ST did not affect the overall number of incontinent episodes (P = 0.078). The Wexner incontinence score dropped from 16.5 +/- 2.5 for pre-SNS therapy to 7.4 +/- 3.1 at the study baseline (P < 0.001). Decreasing the stimulation amplitude to ST, 75% of the ST or 50% of the ST, did not change the Wexner score when compared with the study baseline (P = 0.581). In general, patient satisfaction was high at the study baseline and did not deteriorate as the stimulation amplitude was decreased to 50% of the ST (P = 0.932). Conclusions: Subsensory stimulation as low as 50% of the ST is as effective as stimulation at or above the ST. The study was approved by the Regional Committee on Biomedical Research Ethics, Denmark, and registered at ClinicalTrials.gov (NCT01130870).