Dose Response Curve - Sacral Nerve Stimulation for Faecal Incontinence

The purpose of this study is to determine if subsensory stimulation (amplitude) will maintain same continence in patients treated with Sacral Nerve Stimulation (SNS) for faecal incontinence as stimulation with amplitude at sensory threshold.

Faecal incontinence is a devastating condition with huge impact on quality of life. Sacral Nerve Stimulation (SNS) has since 1995 been a treatment option for patients not obtaining satisfactory continence result with standard non-surgical treatments. SNS is electrical stimulation of the sacral nerve root(s2,3 or 4). Stimulation of this nerve roots results in improved continence. The mechanism of action is at present not well described. Standard the neuromodulator (pacemaker) stimulate with Frequency 14 Hz, pulse width 210 mic.sec. and amplitude set at sensory threshold. One study by SM. Koch et all confirms that subsensory stimulation can be effective. At present there is no doubled blinded study's to confirm this theory of effective sub sensory stimulation. The aim of this study is to determine if subsensory stimulation will be as effective as stimulation with amplitude at sensory threshold. This will be investigated in 20 patients who have had at least a reduction in incontinence episodes or Wexner inc. score of 75 % between preimplantation and latest follow up. The patients will be randomized to three different amplitudes. 1: amplitude set at sensory threshold. 2: 75% of sensory threshold. 3: 50% of sensory threshold. The order of the three settings will be random and in a double blinded manner. The interval between these three pacemaker settings is four weeks. Patients serve as there own controls. Stimulation frequency (14 Hz) and pulse width (210 mic-sec) will remain fixed. Evaluation will be by means of 4 week bowel habit diary and questionnaires (Wexner inc. score / St. Marks Score / Wexner constipation score / Altomares OD-score / IBS-score/ Rockwood FIQoL -score). All patients will be evaluated with anorectal measurements (sphincter strength and anorectal volume measurements) before any changes of stimulation amplitude.

Sacral nerve stimulation with amplitude (sensory threshold), Frequency 14 Hz and pulse width 210 mic.sec.

Sacral nerve stimulation with amplitude (75% of sensory threshold), Frequency 14 Hz and pulse width 210 mic.sec.

Sacral nerve stimulation with amplitude (50% of sensory threshold), Frequency 14 Hz and pulse width 210 mic.sec.

Assess number of incontinence episodes, by means of bowel habit diary. Four week bowel habit diary will be evaluated three times during the twelve-week protocol perioed.

Resting and maximal anal sphincter pressure will be measured with different amplitude settings. In total three evaluations will be made in the twelve week protocol perioed.

Quality of life will be recorded by means of Rockwood faecal incontinence quality of life score. A total of three evaluations will be made every fourth week in the twelve week protocol perioed.

Inclusion Criteria: 18 years or older Informed consent Idiopathic fecal incontinence or Fecal incontinence due to small sphincter defect(≤60 o) fecal incontinence after primary/secondary sphincter repair Permanent neuromodulator (medtronic InterStim / Interstim II) implanted for at least 12 weeks before entering the study. Reduction in fecal incontinence episodes of at least 75% between baseline and latest follow up.(Bowel diary card) or 75% reduction of Wexner Inc. score. Willing and competent to fill out diary cards Exclusion Criteria: Colorectal/proctological surgery since IPG-implant Pregnancy Anorectal Pain

Duelund-Jakobsen J, Buntzen S, Lundby L, Laurberg S. Sacral nerve stimulation at subsensory threshold does not compromise treatment efficacy: results from a randomized, blinded crossover study. Ann Surg. 2013 Feb;257(2):219-23. doi: 10.1097/SLA.0b013e318269d493.