Charles KnowlesCharles Knowles kicks off this month's topic, Faecal Incontinence, with a review of what is known about the efficacy of percutaneous tibial nerve stimulation for treating adults with faecal incontinence.

I get asked this question frequently having led the research which is purported by many to have damned it [1]. However one RCT does not represent the whole story. Here is what I think we know:

  1. Multiple observational studies of PTNS show high success rates for treating adults with FI particularly in reducing urgency [1].
  2. Patients like it with high degrees of satisfaction and almost no adverse effects.
  3. A high quality RCT of 227 adults with FI comparing PTNS to sham stimulation failed to make the primary outcome but did show numerically significant differences in effect between active and sham arms. The effect sizes in this HTA-funded trial (CONFIDeNT study) [2] triangulate almost exactly with a smaller RCT with a similar design performed in mainland Europe [3].
  4. Subsequent Independent sub-analysis of the CONFIDeNT study [4] showed that the presence of baseline evacuatory symptoms significantly and negatively stratified outcome; exclusion of these patients would have completely changed the interpretation of CONFIDeNT to one where the primary outcome would have been met with a high level of statistical confidence.

So what does this mean? It is a fact that RCTs, especially those with an explanatory design, can only test the hypothesis they test, and thence only in the experimental conditions of the trial. Many people don’t seem to get this, preferring to consider the CONFIDeNT trial ‘wrong’ in some way because it didn’t give the answer they expected or wanted. The results of the trial are what they are, and I believe they are correct (as partly evidenced by identical findings in the only other similar RCT [3]). What can however be levelled at the trial is that different inclusion criteria might have yielded a different result (as shown by the independent sub-analysis [4]). Also, CONFIDeNT made no attempt to test how PTNS performs as part of a real-world package of care. I agree that patients like it and also that in practice it seems to objectively benefit some of them. Maybe some of this is the placebo effect; maybe some is the interaction of a caring nurse with the patient. It is on this basis that our service at Barts in London still provides PTNS, albeit after stratifying patients on the basis of the 2017 data.


  1. Horrocks EJ, Thin N, Thaha MA, Taylor SJ, Norton C, Knowles CH. Systematic review of tibial nerve stimulation to treat faecal incontinence. Br J Surg. 2014; 101:457-68.
  2. Knowles CH, Horrocks EJ, Bremner SA, et al. Percutaneous tibial nerve stimulation versus sham electrical stimulation for the treatment of faecal incontinence in adults (CONFIDeNT): a double-blind, multicentre, pragmatic, parallel-group, randomised controlled trial. Lancet 2015;386:1640-8.
  3. van der Wilt AA, Giuliani G, Kubis C, et al. Randomized clinical trial of percutaneous tibial nerve stimulation versus sham electrical stimulation in patients with faecal incontinence. Br J Surg 2017;104:1167-1176.
  4. Horrocks EJ, Chadi SA, Stevens NJ, et al. Factors Associated With Efficacy of Percutaneous Tibial Nerve Stimulation for Fecal Incontinence, Based on Post-Hoc Analysis of Data From a Randomized Trial. Clin Gastroenterol Hepatol 2017;15:1915-1921 e2.