Efficacy of Sacral Nerve Stimulation Before Definitive Implantation (SNStest)

Sacral nerve stimulation (SNS) is an emerging treatment for patients with severe faecal incontinence when conservative measures fail and surgical repair is not indicated. In a minimally-invasive approach and under local anaesthesia, an electrode is placed around sacral nerve root S2-4 and electrical stimulation is applied to the sacral spinal nerves. Effectiveness of SNS is definitively not only explained by placebo effect but the pathophysiologic mechanisms remain unclear. Suggested pathways include modulation of afferent nerve fibres and direct stimulation of the pelvic floor and anal sphincter muscle. After placement of the electrode, the patient is stimulated by an external stimulator for 1-3 weeks. During this period, the patient documents the number of faecal incontinence episodes or urgencies in a symptom diary. By convention, indication for permanent stimulation is based on a 50% reduction in the number of episodes. After a successful testing period, the permanent stimulator is implanted, generally in the upper gluteal region.

Previous studies report success rates up to 80%. The only randomized trial with a proper sample size evaluated the efficacy of SNS after definite implantation. In this study, 63% of the patients felt improved during the placebo period and might not really benefit from the device. The real success rate of SNS is therefore likely to be considerably lower. Efficacy of SNS during the testing phase has never been assessed in a blinded randomized study.