Trial design: Randomised, multicentre, double-blind crossover trial (with 2 × 16-week periods) of active neurostimulation versus sham stimulation with subsequent open-label follow-up to 58 weeks. Embedded mechanistic sub-study using magnetoencephalography to study bidirectional functional connectivity between brain and anorectum.
Methods: Participants: adults aged 18–80 years, with chronic symptoms of faecal incontinence refractory to first-line treatments (and meeting national criteria for sacral neuromodulation). Interventions: active: chronic, subsensory (low amplitude) stimulation of a mixed sacral nerve (usually S3) using a commercially available surgically implanted pulse generator; sham: identical implant but turned off (or to 0.05 V). Patient-chosen sub- or supra-sensory open-label stimulation from week 32 to week 58. Primary objectives: (1) to determine whether sub-sensory sacral neuromodulation led to a reduction in total faecal incontinence episodes per week compared to sham stimulation; (2) to identify whether clinical responses to sub-sensory sacral neuromodulation were biologically related to changes in evoked and induced activity between the brain and anorectum. Primary outcome: total faecal incontinence episodes per week based on paper bowel diary performed in the final 4 weeks of each crossover period (allowing 12-week washout). Randomised allocation (1 : 1) to arm 1 (sacral neuromodulation/sham) or arm 2 (sham/sacral neuromodulation) at time of surgery was stratified by sex and centre. Blinding: participants, surgeons and assessors; tamper-proof tape masked stimulation settings. Statistical methods: Poisson regression models failed to converge for the count outcomes, hence paired t-tests were used, and treatment effects summarised by mean differences [with 95% confidence intervals (CIs)]. Sample size: a total of 90 patients (45 per group) were required to detect a 30% reduction in episodes, allowing for 10% loss to follow-up (alpha = 0.05; power 90%).
Results: Recruitment: a total of 39 patients of 220 screened and 65 pre-enrolled (arm 1: N = 17; arm 2: N = 22) were recruited to the crossover trial at nine sites from the United Kingdom and one site from Ireland between February 2018 and July 2022, of whom only 16 (arm 1: N = 9; arm 2: N = 7) had complete primary outcome data. Nineteen completed follow-up to 58 weeks. Trial delivery was severely affected and terminated early due to COVID-19. Main barriers were the inability to continue face-to-face patient visits, redeployment of research staff to COVID-19 facing clinical roles and cancelling of sacral neuromodulation procedures due to lack of priority for non-urgent surgery. A total of 25 patients underwent magnetoencephalography studies compared to 20 healthy volunteers. Primary outcome (N = 16): sacral neuromodulation conferred a non-significant reduction in mean faecal incontinence episodes per week compared to sham (−0.7, 95% CI −1.5 to 0.0; p = 0.06). Secondary outcomes: in participants who also used the e-event recorder to record the number of faecal incontinence episodes in both periods (n = 7), estimate of effect size was greater but less precise (−1.5, −3.5 to +0.5; p = 0.12). Data suggested successful allocation concealment. Improvements were observed in faecal incontinence symptoms in the follow-up cohort (at 58 weeks) compared to baseline (approx. 3 fewer faecal incontinence episodes per week). A small number of expected adverse events all resolved. Magnetoencephalography studies demonstrated bidirectional afferent evoked cortical and efferent induced anal activity that did not vary greatly from control subjects (n = 20) and appeared unchanged by sacral neuromodulation.
Conclusions: Due to under-recruitment it is important to interpret the findings on the experimental efficacy of sacral neuromodulation as exploratory. Effects on symptoms observed during double-blinded crossover point to some efficacy over sham, though not large in comparison with placebo responses. The magnitude of effect was highly dependent on method and interpretation of event recording.
Study registration: Current Controlled Trials ISRCTN98760715.
Funding: This award was funded by the National Institute for Health and Care Research (NIHR) Efficacy and Mechanism Evaluation (EME) programme (NIHR award ref: 14/144/08) and is published in full in Efficacy and Mechanism Evaluation; Vol. 11, No. 19. See the NIHR Funding and Awards website for further award information.
A treatment called sacral neuromodulation is commonly offered to adults experiencing bowel (faecal) incontinence. A battery powered unit is implanted into the lower back in the region of the sacrum (tailbone). This is connected to a specially developed lead with electrodes that rest on the nerves of the lower spine. This stimulator then continuously sends electrical impulses to the nerves and muscles that control the lower bowel (rectum and anus). The aim is to improve bowel control.
Previous studies have reported a great benefit of sacral neuromodulation in some patients, but others have little or no response. The SUBsensory Sacral Neuromodulation for InContinence trial recruited 39 patients (of 90 intended) who met the current national criteria for sacral neuromodulation. It compared the effect on numbers of weekly faecal incontinence episodes with the device either on (active) or off (sham) using a special study design called a randomised crossover trial. All participants had the device on and off for 16 weeks in random order (crossing over in the middle). Using stimulation below the level that can be felt (subsensory), both the patients and the research team were unaware of whether the stimulator was on or off (called double blinding).
Due to COVID-19, only 16 patients had complete data for analysis, which was much less than the intended number of 90. The results showed that patients experienced reductions in faecal incontinence episodes during both on and off periods (i.e. there was a strong placebo effect). However, slightly greater effects were seen during the on period suggesting a possible genuine biological effect of sacral neuromodulation. The study also showed that the way we record symptoms during research trials for example with paper bowel diaries needs improvement, as the bowel diaries were not fully completed by some participants. Although this is the first double-blind trial of its kind for sacral neuromodulation, all conclusions must bear in mind the poor recruitment and retention of patients.
Copyright © 2024 Vollebregt et al.