Neurostimulation sacrée pour incontinence anale

Sacral nerve stimulation (SNS), a form of peripheral nerve neuromodulation, has been the single most important development in
the treatment of fecal incontinence in the past decade. Introduced initially as a treatment for urinary incontinence, it was adapted by Matzel and others in 1994 for treatment of fecal incontinence with sometimes dramatic success.
Patient selection for SNS is problematic as faecal continence is a complex physiological mechanism and peripheral neuropathy is
only one of several potential component aetiologies in each individual. As yet, there are no preoperative investigations that are
clearly predictive of outcome; however a trial with a reusable external stimulator for 2 to 3 weeks known as peripheral nerve
evaluation (PNE) allows selection of patients who are likely to benefit from permanent implantation. A successful PNE is defined as reduction in incontinence episodes by at least 50%, however the outcome is usually more dramatic. The placebo effect is difficult to overcome, however crossover trials with the stimulator turned on or off suggest a real effect of stimulation. With wider application of PNE, the indications for SNS have evolved over time and there is evidence that it may be suitable for those who in the past may have undergone anal sphincteroplasty as first line treatment. A multicentre prospective randomised trial is being proposed to address this question.
The medium term clinical outcomes of SNS for incontinence seem satisfactory. However with aging comes increasing weakness in
the pelvic floor. As yet there the effects of menopause on outcome are unknown, but recent long term data suggest a gradual
decline in outcome. Device failure is uncommon but reprogramming of the stimulator is sometimes required. The expected battery
lifetime is 5 to 7 years with average current settings.
The mechanisms by which SNS improves continence are not well understood. However, both clinical observation and experimental evidence point towards changes in sensory and autonomic pathways rather than purely motor effects. Peripheral neuromodulation, even for short periods, has been shown experimentally to increase sensory cortical evoked potentials, while clinically SNS increases cortical representation of the anal canal. An interesting observation is that peripheral nerve stimulation in the lower limb in the S3 dermatome has similar effects. The potential of such research is to refine techniques such that patient response may be more easily predicted and perhaps replace PNE. Intermittent peripheral nerve stimulation may prove both feasible and allow implantation of smaller, less expensive and longer lasting devices.