Sacral nerve stimulation reduces corticoanal excitability in patients with faecal incontinence

Background: Sacral nerve stimulation (SNS) can produce symptomatic relief in patients with faecal incontinence. Moreover, peripheral nerve stimulation has been shown to affect brain function. The aim of this study was to determine whether SNS might produce important changes in cortical activity linked to improved continence. Methods: In an experimental study, ten women with intractable faecal incontinence (mean age 51.3 years) were serially mapped with transcranial magnetic stimulation before and immediately after 14 days of temporary SNS (15 Hz, pulse width 210 mu s), and then 2 weeks later. Anal sphincter electromyographic responses were recorded to cortical stimulation of multiple points over a scalp grid covering the bilateral medial cortex. Continence scores, anorectal manometry and rectal sensitivity data were also collected. Results: SNS improved global symptom scores in the majority of patients; mean(s.e.m.) continence scores fell from 16.9(1.6) to 10.6(1.8) (P = 0.042). Cortical mapping showed a consistent decrease in corticoanal representation and overall excitability immediately after SNS compared with baseline (mean(s.e.m.) 38 083(13 669) versus 42 507(13 297) mu V s; P = 0.017), which was reversed 2 weeks after SNS wire removal. Conclusion: SNS produces symptom benefit in patients with faecal incontinence that is associated with a reversible reduction in corticoanal excitability. SNS therefore drives dynamic brain changes that may play a functional role in influencing anal continence.