Video Clips on DVD
- 7-1
Technique for Placement of Preliminary Nerve Evaluation (PNE) in an Office Setting Under Local Anesthesia
- 7-2
Technique for Stage I Implant Under Fluoroscopy
- 7-3
Total System Implantation
Introduction
Sacral nerve stimulation (SNS) was first described in 1981 by Tanagho and Schmidt as a potential “bladder pacemaker” in which pulsatile electrical stimuli are delivered to the S3 nerve roots, thereby regulating many of the functions of pelvic floor neural networks. Since its approval as a medical device in 1994 in Europe and 1997 in the United States, sacral nerve stimulation (SNS) has been used for a variety of micturition disorders worldwide and for chronic pain syndromes in Europe. The InterStim device (Medtronic, Inc., Minneapolis, Minnesota) has been previously approved for treatment of urgency, frequency, urge urinary incontinence, and nonobstructive urinary retention. Studies have also shown a positive effect on defecatory dysfunction, specifically, fecal incontinence and fecal urgency disorders as well as refractory constipation. Based on this data, the FDA has recently added fecal incontinence as an approved indication for placement of InterStim. It has been used for this indication in Europe for a number of years.
The mechanism behind SNS is still, for the most part, unclear. The goal of the device is to provide stimulation to the S3 nerve roots that pass through the S3 foramen. The sacral nerve root contains a variety of somatic, afferent, and efferent motor nerves. These spinal roots are part of the network that controls micturition and bowel function through sensory afferent, parasympathetic, and motor pathways. It is postulated that neuromodulation allows for inhibition of some neurologic signals to the bladder reflex pathways ( Fig. 7-1 ).
Increasingly, the literature on defecatory dysfunction supports the use of neuromodulation for patients with symptoms refractory to maximum conservative therapies. The scope of use has ranged from fecal urgency, fecal incontinence, and severe constipation with impressive success rates at the termination of follow-up.
In March 2010, Wexner et al. published a prospective cohort study that investigated SNS for fecal incontinence in 120 patients who averaged greater than two episodes of loss of stool per week. This multicenter trial aimed to demonstrate >50% symptomatic and objective improvement in reduction of incontinent episodes per week. In addition, they evaluated changes in urgency symptoms and improvement of quality of life (QOL) scores when compared to baseline using the fecal incontinence quality of life (FIQOL) and fecal incontinence severity index (FISI) questionnaires.
Each study patient underwent staged implantation of the InterStim device, and if bowel diaries showed a >50% reduction of incontinent episodes over the trial period, the permanent implantable pulsatile generator (IPG) was placed. After permanent implantation, 83%, 85%, and 87% at 1, 2, and 3 years, respectively, described a >50% reduction of incontinent episodes. Complete continence was reported in 41% of patients.
Quality of life was evaluated at standard intervals. For FIQOL and FISI scales and subscales, quality of life improvement was widely documented. Adverse effects reported were mild and, for the most part, related to incisional pain from IPG placement.
A Cochrane Review in 2009 evaluated the available data on using SNS for fecal incontinence (FI). Included in their analysis was quantification of incontinence episodes, imaging and functional modalities such as ultrasound and manometry to evaluate improvement, and outcomes of a variety of continence QOL questionnaires used in the reviewed studies. All studies were blinded as to when the device was in the off and on position. All of the studies reported the majority of subjects to have a significant improvement number of incontinence episodes. The Cleveland Clinic incontinence scores noted the majority of patients reported improved scores with device stimulation with an average decrease in score (indicating improvement) of 10.5 to 8.3. Each study used different QOL scales; however, all studies reported statistically significant improvement in lifestyle, coping, and depressive symptoms.
Surrogate measures, such as anal manometry, were also evaluated in the review. Resting anal pressure and maximum squeeze pressures were improved when the device was in the “on” position. In addition, sensory perception to rectal distention increased significantly with SNS.
Complications of the device were rare but included pain from the device and recurrent infection of the implant area. Overall, the review admittedly stated that there was still insufficient evidence to promote universal use, but supported further research in the field to establish more conclusive data.
In 2004, Jarret et al. published a comprehensive review of the literature for SNS for fecal incontinence and constipation based on multiple case series and crossover studies. For fecal incontinence, 266 patient cases who had failed conservative therapy were analyzed. The literature review showed that 41% to 75% of patients had complete continence of solid and liquid stool and 75% to 100% reported significant improvement in symptoms (>50% reduction). Patients also reported an improvement in QOL scores after implantation and showed improved ability to prolong the urge to defecate by Cleveland Clinic incontinence scores.
Vaizey et al. showed a decrease in urgency-related symptoms in association with high-pressure colonic contractions. As a result, the anal sphincter response to these colonic increases in pressure was overall fewer anal sphincter relaxations and improved continence.
In some studies there appears to be an increase in maximum anal resting pressures, which may support the theory that SNS has a strengthening effect through both sensory afferent routes as well as striated muscle. This, however, is not consistently supported in the literature, and the true mechanism still remains unclear.
Oom et al., in 2010, also addressed whether SNS for fecal incontinence is indicated in patients with known pelvic floor injury caused by obstetrical or other trauma. Most previous studies had excluded patients with known sphincter disruption or other major anatomic defects. In this study, a cohort of 46 participants was thoroughly evaluated for pelvic floor defects before InterStim implantation. Sphincter and pelvic floor muscle integrity were assessed by three-dimensional (3D) transperineal ultrasound. Twenty-nine participants had documented external anal sphincter (EAS) disruption with or without prior history of obstetrical tear or anal surgery. Over a follow-up period of 32 months, moderate to excellent improvement was reported in 81% of the patients. Furthermore, there was no difference between those women with documented injury versus intact EAS.
In addition to all of the promising evidence that incontinence episodes are markedly decreased by SNS in patients with a good test response, there is also a growing body of literature to refute a placebo effect mechanism. Kenefick et al., in 2006, demonstrated rapid returns to baseline incontinence if the device was turned off in a blinded manner.
Technique for Device Placement
The implantation of an SNS device is a two-step process, composed of a preliminary, or test phase and a final implantation phase (Stage II). The testing phase can be done in a minimally invasive fashion in the office or operating room (OR). The need for fluoroscopic guidance to assist in appropriate placement of the leads depends on the difficulty of placement and surgeon preference.
The device itself, currently second generation, is comprised of a battery-powered stimulator with an average battery life of 4 years. The preliminary procedure (Stage I) historically has involved placement of a permanent lead into the S3 foramen under fluoroscopic guidance in the operating room. A series of four electrodes are present on the permanent (or chronic) wire to assist with proper placement and signal monitoring. Success of the device is measured by percentage improvement with stimulation, specifically, >50% improvement in symptoms after temporary implantation will lead to permanent implantation. The success of the permanent device approaches 100% sensitivity when the test device is effective by these standards. If the lead does not produce an adequate response, it can be easily removed in an office setting or in an outpatient surgery setting.
More recently, preliminary implantation of a temporary lead in an office setting, known as a preliminary nerve evaluation (PNE), has become popularized. Correct positioning is based on motor and sensory responses ( Table 7-1 ), but may also be placed under fluoroscopy if available. The trial period is generally 1 to 2 weeks depending on the disorder and patient perception of success. If symptomatic improvement occurs, the patient may proceed to surgical implantation in the upper buttocks of the electric pulse generator (total system implantation).
