7-2 Sacral Nerve Stimulation

Joanna M.Togami and Gamal M. Ghoniem

Sacral nerve stimulation (SNS) is a useful tool to have in stress incontinence, and high frequency (200Hz) for the armamentarium for the treatment of voiding dysfunc- . A review of trials of functional electri- tion. Since Food and Drug Administration approval, SNS cal stimulation for stress showed cure has evolved to attain a major role in treating refractory in 18% and improvement in 34% of patients. In the treat- overactive bladder (OAB) and patients with difficult pelvic ment of OAB, maximal electrostimulation cured 20% and floor dysfunction. It has become a viable option in those improved 37% of women with urodynamic detrusor over- patients who failed conservative therapy, but who desire activity incontinence.1 Functional electrical stimulation is alternative therapy before more invasive procedures are of limited value in the treatment of stress incontinence. performed. The technique and the technology have been improved, increasing the safety and efficacy whereas decreasing patient morbidity. Mechanism of Action

The precise mechanism of action by which electrical stim- Functional Electrical Stimulation ulation works remains to be proven. It is thought that the efficacy is dependent on stimulation of the afferent nerves Electrical stimulation has been used for a variety of lower that modulate sensory processing of the voiding reflex and urinary tract symptoms including those of OAB and its pathways to the central nervous system. Several voiding painful bladder syndrome. There are mainly two types of reflexes are affected by neuromodulation, and it is useful electrical stimulation: chronic, in which low current is used to review these. The guarding reflex serves to maintain for many hours daily, and acute submaximal functional continence with increased bladder volume. The detrusor electrical stimulation, which is applied up to the patient’s muscle relaxes, the levator ani muscles contract, and tolerance for 15 minutes, once or twice a day, three times a urinary leakage is prevented. The micturition reflex facili- week, or daily. The stimulation can be applied transvagi- tates voiding. Normally, a voluntary signal to empty the nally, transrectally, or transcutaneously. There are a variety bladder originates from the cerebral cortex. The pontine of home units that can be used by the patient. micturition center acts as a switch between the guarding The proposed mechanism of action is alteration of lower reflex and the micturition reflex.After sensory information urinary tract function by stimulation of the sacral auto- is processed in the pontine micturition center, micturition nomic or somatic nerves. There may also be a direct stim- is initiated under voluntary control. This is mediated by ulatory effect on pelvic floor muscles and sphincters afferent delta nerve fibers and is composed of two reflexes. causing muscular hypertrophy and a change from fast- The bladder-bladder reflex is a positive reflex that activates twitch to slow-twitch fiber types, which can maintain the full bladder allowing a sustained contraction until the muscle tone more effectively. bladder empties. The bladder-urethra reflex allows smooth The stimulation probe is placed in the vagina at the level muscle of the proximal urethra to remain open while the of the pelvic musculature in the mid-vagina. During stim- bladder contracts. One theory is that these reflexes become ulation, the probe is held by the patient to prevent any pathological with voiding dysfunction. For bladder over- migration and possible discomfort. Functional electrical activity, SNS may work by inhibition of several neurons: stimulation current is pulsed, i.e., short periods of stimu- spinal tract neurons involved in the micturition reflex, lation are alternated with longer rest periods. The strength interneurons involved in spinal segmental reflexes, and of the stimulus is adjusted to avoid pain. Low frequency postganglionic neurons, thus inhibiting the primary affer- (10–20Hz) is used for OAB, mid-frequency (50–100Hz) for ent pathway.2 For nonobstructed urinary retention, SNS 175 176 Urgency/Frequency Syndromes Therapy may suppress the guarding reflex by turning off bladder sacral spinal cord injury, radical pelvic surgery, spinal cord afferent input to the internal sphincter sympathetic or tumors, and those with areflexic bladders from myogenic external urethral sphincter interneurons, and activation of damage secondary to chronic overdistention. postganglionic neurons and including bladder activity.2 Stimulation is not curative for the underlying condition, and symptoms will recur when stimulation has been Nerve Evaluation turned off. However, by modulating these reflexes that have become aberrant, symptoms improve. Before placement of the permanent pulse generator, it is useful to evaluate the sacral nerve to assess its suitability for stimulation. The purpose is to confirm the integrity of Indications the peripheral nerves. Also, it can identify the optimal site for a trial of temporary stimulation. This may be per- Sacral neuromodulation is indicated in urgency frequency, formed by one of two methods – percutaneous nerve eval- urge incontinence, mixed incontinence with a significant uation (PNE) or staged implantation of the permanent urge component, and unobstructed urinary retention. lead.We use the PNE in patients who have urgency and fre- More recently, it is indicated for . The quency. Patients who are being treated for nonobstructed work-up includes a complete history and physical exami- urinary retention generally undergo a staged procedure. nation, urinalysis, urine culture, cytology, and voiding This allows for a longer period of evaluation, because diary. Cystoscopy, urodynamics, and upper tract imaging retention generally improves over a week to 10 days, are performed as indicated. These diagnostics serve three whereas with urgency and frequency, the results are gen- purposes: 1) to identify an underlying disorder that should erally apparent within several days. The advantages of the be treated by other means (calculus or carcinoma in situ), PNE are that it is performed as an office procedure, it is 2) to clarify the etiology of the lower urinary tract dys- completely percutaneous, and the wires can be removed function, and 3) to serve as a baseline for later comparison. simply by pulling them out. The drawbacks are that lead migration occurs in 12% of patients and there is a poten- tial difference of approximately 15%, in clinical response Contraindications when the permanent lead is placed with the internal pulse generator. The advantage of the staged procedure is that Mental incapacity is a contraindication, because the patient the permanent lead is placed during the first stage; there- must be able to adjust the patient programmer used to turn fore, the clinical response when the internal pulse genera- the stimulator on and off. In addition, the patient must be tor is inserted is the same, because lead migration is able to track and understand the response to therapy. Elec- minimal. The disadvantages are that a small open incision tromagnetic interference can result in injury to the patient is needed to implant the lead, and a separate procedure is from heating of the implanted components of the system, necessary to explant the lead should the test period be resulting in damage to the tissues. System damage may unsuccessful. require surgical replacement. Operational changes to the neurostimulator from a magnetic source can potentially turn the system off, resulting in resumption of symptoms. Technique This may require reprogramming. Unexpected changes in stimulation can result in a shock or jolt-type sensation. The method for implantation of the lead and the wires is Sources of electromagnetic interference include defibrilla- similar. The patient is placed in the prone position with a tors, cardioverters, electrocautery, high-output ultrasonics 30-degree flexion at the hips. This position places S3, S4, or lithotripsy, magnetic resonance imaging and radiofre- and S5 into the vertical plane. The patient is given local quency, or microwave ablation. Use of magnetic resonance anesthesia and, under fluoroscopic guidance, the S3 sacral imaging and radiofrequency or microwave ablation can foramen is located using a crossed-hair technique devel- cause tissue damage.3 Diathermy, or energy from the oped by Chai and Mamo.4 diathermy (shortwave, microwave, or ultrasound) can be The horizontal axis is defined at the inferior borders of transferred through the implanted system and cause tissue the sacroiliac joints, and the vertical axis is the midline damage at the site of the implanted electrodes. Diathermy (Figure 7-2.1). Once these are marked on the skin, points is contraindicated in patients with InterStim. that are 2cm lateral and cephalad on both sides are marked. This is the skin location of S3. We identify a point 2 to 3cm above this mark and infiltrate with 2% lidocaine. Patient Selection The needle is introduced at an angle of 60 degrees (Figure 7-2.2). Sacral neuromodulation is ineffective for the following Once the foramen is located, on both anterior/posterior patient populations: those with end-stage, small, con- and lateral views, the needle is stimulated. Both the motor tracted bladders; those with peripheral nerve damage, e.g., and sensory responses are monitored. The lead is Sacral Nerve Stimulation 177

Table 7-2.1. Motor and sensory responses observed with stimulation of the S2, S3, and S4 S2 S3 S4 Motor • Lateral rotation of • Bellows (contraction • Bellows activation the leg of the levator ani of the posterior • Contraction of the muscles causing a levator ani muscles toe and foot deepening and • No motor response • Contraction of the flattening of the of the leg or foot calf buttocks groove) • Contraction of the • Plantar flexion of superficial pelvic the hallux caused floor by sciatic nerve stimulation Sensory • Pulling sensation • Paresthesia of the • Pulling sensation of the vagina or perineal skin, in the rectum base of the penis external genitalia • Pulling sensation of the vagina, rectum, or bladder base

Figure 7-2.1. Crossed-hair technique.

rostimulator pocket site in the upper buttock. A trocar is used to tunnel the lead to the neurostimulator pocket, the quadripolar, and each one is stimulated separately to deter- percutaneous lead extension is connected, and the connec- mine the lead that has the most optimal placement. Table tion is buried at the site. The wires are brought out at a sep- 7-2.1 is a guide for motor and sensory responses observed arate site, usually the contralateral side, and the connection with stimulation of the S2, S3, and S4 nerves. site is closed in two layers. Once the placement is confirmed,either the wire or tined During the second stage, the patient is brought back lead is placed. The wire is fed through the foramen needle. to the operating room and given local anesthesia with The needle is removed, and the wires are then taped care- sedation. The pocket is opened, and the lead is discon- fully to the back. In the case of the staged implant, the lead nected from the extension wire. The wires are pulled out is placed through a sheath, and its placement is verified by from the externalized side to prevent the exposed wires fluoroscopy. A small incision is created at the future neu- from being brought through the subcutaneous tissues. The

Figure 7-2.2. Appropriate needle orien- tation within S3 foramen. The needle entry is 60 degrees to the horizontal. (Reprinted with the permission of The Cleveland Clinic Foundation.) 178 Urgency/Frequency Syndromes Therapy

day decreased from 17 to 10.6. Improvement in the degree of urgency was reduced as demonstrated by 69% of patients. Volume of urine per void increased from 132 to 225mL. Adverse effects were lead migration (18.2%), pain at the implantation site (15.3%), new pain (9.0%), sus- pected lead migration (8.4%), infection (6.1%), adverse change in bowel function (3.0%), suspected device prob- lems (1.6%), nerve injury (0.5%), device rejection (0.5%), and other (9.5%).

Idiopathic Nonobstructive Urinary Retention

Jonas et al.6 studied 177 patients with urinary retention, of which 68 qualified for implantation. They found that 69% of patients eliminated catheterization at 6 months and an additional 14% had a 50% or greater reduction in catheter- ized volume per catheterization. Compared with the Figure 7-2.3. Lateral view of radiograph showing the implanted lead. control group with 9% improvement, 83% of patients achieved successful results. Temporary inactivation of sacral stimulation led to increased residual volumes. pocket is developed for the neurostimulator. The lead is Success was measured as a 50% or greater improvement in connected to the neurostimulator. Connections are sealed baseline voiding symptoms (number of catheterizations with silicone glue and the boot is placed over the connec- per day, total catheter volume per day, maximum catheter tion and tied with prolene suture. Care is taken not to volume, number of voids, and total volume of voids). create a trigger point by placing the wires around the neu- rostimulator. The wound is closed in two layers (Figure 7- 2.3). Interstitial Cystitis Because a foreign body is being introduced into the patient, prevention of wound infections is imperative. We Maher et al.7 studied 15 women prospectively and found administer preoperative antibiotics to cover coliforms and increases in mean voided volume (90–143mL), frequency skin flora.For the first stage and complete implantation,the decreased from 20 to 11, nocturia decreased from 6 to 2 patient is placed in an operating room equipped with times, and mean bladder pain decreased from 8.9 to 2.4 laminar airflow. The pocket developed for the neurostimu- points on a scale of 1 to 10. Quality-of-life measures, lator is irrigated copiously with neomycin irrigation. It is namely, the UDI-6 (the short form of urogenital distress important not to immerse the neurostimulator in a liquid inventory) and SF-36 Health Survey also showed improved medium because this may cause it to malfunction. A two- parameters during the stimulation period. Sacral neuro- layer closure is desirable should the skin open, so that there modulation shows promise for both the urgency/frequency is a closed layer beneath. and pain components of interstitial cystitis.

Clinical Uses

Urgency/Frequency Syndromes and Urge Sacral nerve stimulation has been used for fecal inconti- Urinary Incontinence nence. Ganio et al.8 studied 23 patients with a two-staged approach, five of whom went on to be implanted. Patients In a prospective, multinational study, Siegel et al.5 reported had fecal incontinence at least twice every 2 weeks for 2 on 112 patients with urge incontinence,urgency/frequency, months, failed biofeedback therapy, and had structurally or urinary retention. Follow-up ranged from 18 to 36 intact external and internal anal sphincters. Sphincter dys- months with all three groups showing significant improve- function was demonstrated with fecal incontinence associ- ment. The urge incontinence group noted a decrease in ated with low resting and/or squeeze pressures. Seventeen leaks per day from 11.6 to 5.0. Fifty-nine percent had patients had reduction of liquid or solid stool losses by greater than 50% reduction in leaks,and 46% reported they more than 50%, and 14 were completely continent to both were completely dry. Heavy leaking episodes decreased to liquid and solid stool. In patients with urge incontinence, an average of 1.3 per day. The number of pads/diapers there was a decrease in losses per week from five to one. replaced was reduced from 6.7 pads to 3.4 pads per day. In Manovolumetric findings showed improvements in the urgency/frequency group, average reported voids per maximum resting pressure, rectal sensitivity, first sensa- Sacral Nerve Stimulation 179 tion, and the distention pressure for urge threshold. Two incontinence in women: a systematic review of randomised clinical patients who also had voiding complaints had complete trials. BJU Int 2000;85:254–263. resolution after SNS. Sacral nerve stimulation for fecal 2. Chancellor MB, Leng W. The mechanism of action of sacral nerve stimulation in the treatment of detrusor overactivity and urinary incontinence is currently being studied at our institution. retention. In: Jonas U, Grünewald V, eds. New Perspectives in Sacral Nerve Stimulation for Control of Lower Urinary Tract Dysfunction. London: Martin Dunitz; 2002. 3. Medtronic Inc. medical technology company official company Complications Web site. Available at: http://www.medtronic.com. Accessed May 6, 2004. Reported adverse events include lead migration, new pain 4. Chai TC, Mamo GJ. Modified techniques of S3 foramen localization (at the site or from other nerve stimulation),persistent skin and lead implantation in S3 neuromodulation. Urology 2001;58:786– irritation, change in bowel function, change in bladder 790. 5. Siegel SW,Catanzaro F,Dijkema HE, et al. Long-term results of a mul- function, local infection, technical problem, device ticenter study on sacral nerve stimulation for treatment of urinary 9 problem, and transient electric shock. If the lead is placed urge incontinence, urgency-frequency and retention. Urology 2000; as a first stage, it is recommended that the lead be dissected 56(S1):87–91. out and removed from the original insertion point rather 6. Jonas U, Fowler CJ, Chancellor MB, et al. Efficacy of sacral nerve stim- than from the tunneled skin site because lead breakage has ulation for urinary retention: Results 18 months after implantation. J Urol 2001;165:15–19. been reported. Very few patients have had surgical inter- 7. Maher CF, Carey MP, Dwyer PL, Schluter PL. Percutaneous sacral vention with adverse effects of SNS. In the original series, nerve root neuromodulation for intractable interstitial cystitis. J Urol only one patient required explantation. 2001;165:884–886. 8. Ganio E, Luc AR, Clerico G, Trompetto M. Sacral nerve stimulation for treatment of fecal incontinence. Dis Colon Rectum 2001;44: 619–631. References 9. Jonas U, van den Hombergh U. Complications of sacral nerve stimu- lation. In: Jonas U, Grünewald V. New Perspectives in Sacral Nerve 1. Berghmans LC, Hendriks HJ, DeBie RA, van Waalwijk van Doom ES, Stimulation for Control of Lower Urinary Tract Dysfunction. London: Bo K, van Kerrebroeck PE. Conservative treatment of urge urinary Martin Dunitz; 2002.