Sacral Nerve Stimulation

Autor: Harald R. Rosen - Wien

All patients have to undergo extensive pre-operative evaluation including clinical inspection, the completion of a standardized incontinence diary over a period of three weeks, anal sphincter manometry and endoanal ultrasound and/or magnetic resonance imaging.

A saline retention test after the application of  saline at a volume causing the first urge for defecation  is performed and the maximal time span from the end of instillation to the first evacuation of saline was documented.

Subjects  are regarded as candidates for SNS if they presented a minimum of one incontinence episode per week during the three-week observation period documented in their continence diary. Furthermore, no structural defects have to be observed in the external anal sphincter either on endoanal ultrasound or on MRI. Failed treatment with a 6-week course in bio-feedback must also be reported in all patients.

Patients with neurologically caused incontinence have to present a minimal history of one year in order to exclude patients with a spontaneous recovery following trauma or spinal cord surgery.

Under general or local anesthesia, four to six needles  are positioned into the foramina S2 to S4 bilaterally, and stimulation is performed by the use of an external pulse generator (Screener, model 3625, Medtronic, Minneapolis, Minnesota, USA).

The muscular response of the pelvic floor and the anal sphincters is evaluated visually with both buttocks fixed firmly in order to differentiate pelvic floor response from a possible gluteal contraction. Additionally, intraoperative anal manometry or EMG can be  performed.

Following a positive stimulation response of the pelvic floor and/or the anal sphincters, the subsequent procedure of SNS is performed according to the recommendations for urological  indications. In order to evaluate the functional relevance of positive electric stimulation, a percutaneous nerve evaluation (PNE) is performed by application of a temporary stimulation wire which is introduced into the stimulation needle and fixed to the skin.

The functional result of stimulation is recorded over a period of 10 - 21 days and is followed by a final saline retention test. Patients whose continence status improves undergo permanent implantation of a pulse generator  (INTERSTIM, Medtronic, Kerkrade, Netherlands). During this procedure the permanent electrode is implanted at the site of the external stimulation wire and then connected to the subcutaneous pulse generator by application of an extension kit.   

Acute (needle) testing revealed a typical positive visual response (i.e. contraction of the pelvic floor in a cranial-ventral direction and circular contraction of the anal sphincter) in 16 patients who underwent  subsequently permanent implantation. In 4 patients (fecal incontinence following spinal cord trauma after a car accident: 2 , spinal stroke, and meningomyelocele) the acute testing failed to show any response.  

All patients who had shown a positive visual response during acute testing  and who had received a permanent implant revealed a marked reduction in their incontinence episodes as well as an increase in the time span during saline retention tests .

The median number of incontinence episodes for solid or liquid stool per 21 days decreased from 6 episodes (3 – 15 / 21 days) to  2 (0 – 5 / 21 days) in the total series of 16 implanted patients. Patients (n:4) with idiopathic incontinence revealed 3,3,4,and 6 episodes respectively preoperatively compared with  0,0,0, and 2 episodes postoperatively. The median number of incontinence episodes in neuro patients (n: 12) was preoperative  7 (4  - 15) and postoperative 2 (0 – 5) (p < 0.01) .

The time period of retention of  a volume of saline causing an urge  until definitive defecation was preoperative 2 min (0 – 5 min) and raised to 7.5 min ( 2 – 15 min). In idiopathic patients the preoperative measurements were 2,2,5,and 7 minutes and (postoperative) 2, 10,10,and 15 minutes, respectively.

In the group with neurological incontinence the preoperative retention test revealed a median time of  2 min (0-5 min ) compared with 7 min (2 – 15 min) (p< 0.01) .

As the most prominent observation, patients with neurologically induced incontinence and two patients with idiopathic incontinence  reported a restoration of their anal sensory function. This consisted of an improvement in the sensory capacity of the rectum ampulla as well as the restoration of sensory function perianally  and the perineal skin.

This was nicely shown by two patients in the idiopathic group who did not report any feeling in the rectum  up to the maximal distension of the balloon (i.e. 300 ml) and who reported a complete recovery of their sensory function following SNS  

Three patients who had to undergo a complete explant of the stimulation system due to infections (one patient with meningomyolocele, one with Friedreich’s ataxia and one with idiopathic incontinence) reported an immediate deterioration of their continence function following explantation of the system. After  of the infectious situation, all of them were rated as candidates for renewed sacral nerve stimulation. Until the control date (Mar. 1, 2001) one patient underwent a successful reimplantation  while two others are still waiting for a new SNS.

Contrary to other reports, the main indication in our series was incontinence of neurological origin (n: 15), usually following spinal cord trauma or as a complication after spinal cord surgery for protrusion. While 4 patients showed no pelvic floor and/or anal sphincter response during acute testing, 15 patients achieved a marked improvement or even complete restoration of their continence status, as shown by a reduction in the number of incontinence episodes per week as well as by an increase in the retention time.

The positive stimulation response during acute testing was confirmed visually by the typical contraction features of the pelvic floor and the anal sphincters and significant changes in postoperative anal manometry (3 months postoperatively) were observed.  We were able to demonstrate a significant increase in sphincter pressures and anal canal length which we attribute to the larger number of patients (compared to previous publications) in our series.

Neuromodulation of sacral reflexes and regulation of rectal sensitivity appear to be the major reasons for the functional improvement in our neurological patients following SNS. Although difficult to objectify by diagnostic instruments, all patients showed a successful response, and reported a marked improvement in their rectal sensory function as well as in perianal and perineal sensitivity. Especially in patients following spinal cord trauma in the lumbar region (L1 to L5) , the notion of overcoming the neurological defect by a more distally applied stimulation is a novel approach. Neurophysiologic investigations like pudendal nerve latency measurement which might be able to demonstrate the effects of SNS were not performed in our series. Beside the lack of equipment for these procedures at our institutions these investigations have always been restricted to very specialized departments and have been criticized  for their interobserver variability as well as their limited clinical relevance.

Our preliminary experience showed that the surgical management of patients with fecal incontinence might differ considerably from that of urological patients. While an effective influence of SNS on the urinary bladder can only be evaluated during an observation period of 2-3 weeks involving repeated measurements of the residual bladder volume , a typical positive response to external stimulation during acute testing in fecal incontinence was associated with improved function in almost all of our patients reported in this series. Furthermore, 3 patients developed severe infection of the implanted material, which led to explantation of the stimulation system despite a positive influence on continence function; the infection had probably occurred during the external stimulation  process. Therefore, we altered our concept to an immediate implant during a one-stage procedure following a positive pelvic floor/and or sphincter response after needle stimulation.

Referring to the concerns regarding the implantation of a cost-intensive system and the potentially inadequate functional outcome, it should be emphasized that all patients in the present series had severe fecal incontinence that was therapy refractory to other treatment modalities. In the past, most of the patients with such severe incontinence had been candidates for dynamic graciloplasty at our institution . This means that, in the event of an unsatisfactory functional outcome despite a positive pelvic floor response during acute  testing , the patient would be a candidate for dynamic graciloplasty, which could be applied by using the previously implanted pulse generator.

We conclude that, in our very preliminary experience, sacral nerve stimulation has shown promising results in the treatment of fecal incontinence of neurological etiology as well as due to an idiopathic diffuse weakness of the pelvic floor. Although a longer follow-up is mandatory to assess the long-term efficacy of this method, the initial promising results warrant further clinical studies focusing on this new modality.