Clinical efficacy of subsensory sacral neuromodulation in adults with faecal incontinence: The SUBSoNIC crossover randomised controlled trial and cohort follow‐up study

Aim:
Sacral neuromodulation (SNM) is considered the first-line surgical treatment in adults with refractory faecal incontinence (FI). However, its clinical efficacy has not been rigorously tested in a trial setting.

Method:
Randomised, multicentre, double-blind crossover trial (two 16-week periods) of active stimulation versus sham, and open-label follow-up to 58 weeks. Participants: adults aged 18–80 with refractory FI. Interventions: Active: subsensory sacral nerve stimulation with an implanted pulse generator; Sham: identical implant but turned off. Primary outcome: FI episodes per week (paper bowel diary) during final 4 weeks of crossover periods (allowing 12 weeks' washout). Randomised allocation (1:1) to arm 1 (SNM/sham) or arm 2 (sham/SNM). Blinding: participants, surgeons, assessors; tamper-proof tape-masked stimulation settings. Sample size: 80 patients to detect a 30% reduction in episodes. Groups compared using a paired t-test, and treatment effects summarised by mean differences.

Results:
Trial delivery was severely affected by COVID-19. Thirty-nine patients of 220 screened (arm 1: N = 17; arm 2: N = 22) were recruited at 10 sites (February 2018–July 2022), of whom only 16 (arm 1: N = 9; arm 2: N = 7) had complete primary outcome data. Of the 39, 19 completed follow-up to 58 weeks. SNM conferred a non-significant reduction in mean FI episodes per week compared to sham (−0.795 [95% CI: −1.5 to 0.0], p = 0.06). Improvements were observed in FI symptoms at 58 weeks compared to baseline (FI episodes per week: 3.2 [SD 3.3] vs. 6.2 [SD 5.9]).

Conclusions:
The SUBSoNIC trial failed to find conclusive evidence of the experimental efficacy of SNM. Further demonstration of experimental efficacy remains important as SNM is a high-cost and invasive therapy.