A Cochrane review included six crossover trials and two parallel group trials. Six trials assessed the effects of SNS for faecal incontinence (FI). No meta-analysis was done.
In the first group trial 53 participants with severe FI in the SNS group experienced fewer episodes of faecal incontinence compared to the control group who received optimal medical therapy (MD −5.20, 95% CI −9.15 to −1.25 at 3 months; MD −6.30, 95% CI −10.34 to −2.26 at 12 months). Adverse events were reported in a proportion of participants: pain at implant site (6%), seroma (2%) and excessive tingling in the vaginal region (9%). In the other parallel group trial 5 participants with FI in the SNS group experienced fewer episodes of FI compared with the percutaneous tibial nerve stimulation (PTNS) group (MD −3.00, 95% CI −6.61 to 0.61 at 3 months; MD −3.20, 95% CI −7.14 to 0.74 at 12 months). Adverse events were reported in three participants: mild ipsilateral leg pain during temporary testing (n = 1); and stimulator-site pain following insertion of neurostimulator (n = 2).
Two out of four small crossover studies reported less FI periods when the SNS device was "on" than "off", while two studies showed no difference.
In two trials, SNS did not improve symptoms in patients with constipation.
The majority of participants (22 of 36) suffered from urge incontinence. Both were crossover studies the other including 34 patients and the other 2 patients. In the bigger study the patients, while still blinded, chose the period of stimulation they had preferred. Outcomes at different time points were reported separately for 19 participants who preferred the 'on' and five who preferred the 'off' period. 10 patients prematurely discontinued the study. For the group of 19, the median (range) episodes of faecal incontinence per week fell from 1.7 (0 to 9) during the 'off' period to 0.7 (0 to 5) during the 'on' period; for the group of five, however, the median (range) rose from 1.7 (0 to 11) during the 'off' period compared with 3.7 (0 to 11) during the 'on' period. In the study of 2 patients, an average of six versus one episodes of faecal incontinence per week were reported during the 'off' and 'on' periods respectively. 4 of 27 participants in the bigger study experienced an adverse event resulting in removal of the stimulator.Comment: The quality of evidence is downgraded by study quality and by imprecise results (few patients).