Emerging data for SNS suggest maintenance of its initial therapeutic effect into the long term. The clinical effectiveness of PTNS is comparable to that of SNS at 12 months, although there is no evidence to support its continued effectiveness after this period. PTNS may be a useful treatment before SNS. The clinical effectiveness of TTNS is still uncertain owing to the paucity of available evidence. A consensus to standardize the use of outcome measures is recommended in order that further reports can be compared meaningfully.

The limited evidence from the included trials suggests that SNS can improve continence in a proportion of patients with faecal incontinence. However, SNS did not improve symptoms in patients with constipation. In addition, adverse events occurred in some patients where these were reported. Rigorous high quality randomised trials are needed to allow the effects of SNS for these conditions to be assessed with more certainty.

There is considerable disagreement between the results of various tests used to diagnose ED and FDD. This highlights the need for a reappraisal of both diagnostic criteria, and what represents the 'gold standard' investigation.

Most patients with chronic constipation secondary to ED with rectal hyposensitivity responded to temporary SNS. The physiological results presented support a mechanistic role for rectal afferent modulation.

In the short term, both SNS and PTNS provide some clinical benefit to patients with FI. Registration numbers: 2010-018728-15 and 10479 (http://public.ukcrn.org.uk/search/StudyDetail.aspx?StudyID=10479).

PTNS and TTNS result in significant improvements in some outcome measures; however, TTNS was not superior to sham stimulation in a large, adequately powered, RCT. As no adequate RCT of PTNS versus sham has been conducted, conclusions cannot be drawn regarding this treatment.

Sacral nerve stimulation appears to be an effective treatment for patients who do not gain an adequate therapeutic benefit from percutaneous tibial nerve stimulation and, thus, should be routinely considered for this patient cohort.

Alteration of pulse width or frequency of stimulation had no significant effect on the outcome of SNS for constipation.