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01 May 2010
Sacral nerve stimulation (SNS) is similar to Spinal Cord Stimulation and is a minimally invasive procedure that involves implanting a device that applies low currents of electrical stimulation to the sacral nerves at the base of the spine. Nerve stimulation is referred to by some pain experts as a “pacemaker for pain”. It works by sending a small electrical impulse created by a compact generator through thin leads, or electrical cables, to targeted nerves, where they block pain signals traveling to the brain. Pain is replaced with a mild tingling or massaging sensation, called paresthesias. A wireless remote control is used to adjust the location and degree of stimulation by selecting pre-programmed settings.
Spinal cord stimulation was first reported for the treatment of chronic pain in the 1960s by directly implanting the device on the dorsal column of the spinal cord (1). Tanagho and Schmidt were the first to perform SNS with initial indications for urinary urge incontinence, urgency-frequency, and urinary retention in 1981. Since then, SNS has been used to successfully to treat several conditions including interstitial cystitis (IC), prostatitis, vulvodynia, pelvic floor dysfunction, neuropathic foot pain, pelvic nerve pain, anal pain, and testicular pain. The current treatment options for many of these conditions are not effective and are accompanied with unpleasant or dangerous side effects. Recent research has shown promising results for SNS. SNS has been primarily utilized to improve urinary tract function, but its role as a modality of treatment for pain is growing quickly. After conservative treatment with rest, medical treatment, physical therapy, chiropractic, interventional procedures and/or surgery have failed, SNS may provide a safe and effective treatment option.
Anatomy
There are five sacral nerves that branch from the spinal cord and emerge from the sacrum, or lower portion of the spine. These nerves are formed from nerve roots that originate from both the front and back of the spinal cord. On the posterior, or back side, the nerves exit through a hole in the sacrum called the posterior sacral foramina and form the posterior branches of the sacral nerves. On the anterior, or front side, they exit the anterior sacral foramina and form the sacral plexus and coccygeal plexus. A plexus is a networks of interconnecting nerves, of which there are several in the human body. Although the vertebral components of the sacrum are fused into a single bone, the sacral vertebrae are still used to number the sacral nerves (S1-S5).
Each spinal root supplies sensory innervations to a specific area of skin called a dermatome. Lesions of specific nerve roots result in predictable pattern of signs and symptoms. For instance, a lesion in a lumbar nerve root may cause muscle weakness, numbness, tingling, and/or reflex changes in the legs. This gives physicians a tool for localizing the lesion that is causing the symptoms. Imaging modalities, such as an MRI, may be used to assist and confirm a diagnosis.
Description
SNS is a minimally invasive procedure that is done on an outpatient or short hospital stay basis. There are two steps to the procedure, a trial procedure and a permanent implant. The trial procedure is a brief procedure that is usually done under light sedation. The area where the leads are implanted is numbed with local anesthesia. One or more needles are directed under x-ray guidance into the epidural space, which is the area surrounding the spinal cord and/or nerve roots. The sacral area is below the actual spinal cord, which eliminates the risk of spinal cord damage. The leads are then placed through a needle and are positioned to the desired location next to the sacral nerves. The leads are then connected to an external generator. Once the generator is turned on, the impulses are sent with varying intensities to different positions of the lead. The patient will sense paresthesias (tingling and/or buzzing) while a programmer adjusts the settings to provide the “best coverage.” These settings are then saved on the remote control so that the patient can adjust the stimulator to best fit their needs. The trial period usually lasts a few days to a week, depending on the effectiveness of the SNS. The goal is to test the stimulator’s effectiveness at relieving pain and increasing normal activities throughout a day.
If at the end of the trial period the pain relief is sufficient (usually 50% or greater), then the trial is deemed a success and a permanent implant may be scheduled. The permanent procedure is carried out in similar fashion to the trial procedure. The significant difference is that the generator is implanted, like a pacemaker, in a subcutaneous pocket. Usually the upper, outer quadrant of the buttock is chosen, which results in a largely unrecognizable and comfortable experience. A few small bandages will be applied over the incisions. After the procedure, the patient can usually return home the same or following day.
Benefits
SNS has been used to successfully treat chronic pelvic pain, as well as other pain syndromes. For more than a decade, the safety of SNS has been proven in its use treating refractory urinary urge incontinence (2). One study suggested that neuropathic pain and complex regional pain syndromes may also be treated successfully with neurostimulation applied to dorsal columns and peripheral nerves (3). In fact, 73% of women with intractable interstitial cystitis experienced a reduction in pelvic pain from SNS (4). A 2003 study found SNS provides symptomatic relief of pelvic pain and encouraged neuromodulation to be “used earlier in the treatment paradigm for these disorders, before the potentially injurious procedures of hydrodistention, bladder installations, and cystectomies” (5). Another rather small study reported that SNS resulted in adequate paresthesia coverage and effective pain relief for vulvodynia (6).
Intractable interstitial cystitis (IC) is defined as patients with IC that have failed conventional therapy. In this case, the only traditionally available therapeutic option for IC was extensive surgery (7). A prospective clinical study showed that “sacral neuromodulation is a safe and effective treatment for the pelvic pain in patients with interstitial cystitis who are refractory to other forms of treatment” (8). A 2004 study demonstrated “a reduction in morphine dose equivalents by 36% in patients with refractory IC and chronic pelvic pain”, and “approximately 20% of patients were actually able to stop their narcotic medications” due to the results of SNS (9).
Recent studies have opened the possibility of broadening the indication of SNS. A 2009 study encouraged that SNS should be considered before surgery for patients “with chronic idiopathic anal pain in whom pharmacologic and biofeedback treatments have failed to produce effective results” (10). A recent case study demonstrated the “potential therapeutic benefit of SNS for neuropathic intractable testicular pain in a patient that failed conservative treatment” (11).
SNS offers many desirable benefits, which include being less invasive than surgery, reversible/removable, adjustable, and testable. In the future, SNS may be considered for penile pain, vaginal pain, and other pain conditions. Ultimately, SNS may permit an individual to return to their daily activities, have less pain, travel unrestricted, enjoy recreational activities, and improve their well-being and overall quality-of-life.
Risks
As with any surgical procedure, there are risks, including: infection, bleeding, nerve damage and allergic reaction. In addition, there are specific risks to nerve stimulation. These may include: headache, equipment failure that leads to intermittent or no stimulation, over-stimulation, disconnection, and lead migration, which may require additional procedures to correct. The most common problem is lead migration (12). In fact, one study documented an average lead migration of a centimeter or more (13).
References
1) Shealy CN, Mortimer JT, and Resnick J. Electrical inhibition of pain by stimulation of the dorsal columns: Preliminary reports. J. Int. Anesth. Res. Soc, 46:489-491, 1967. 2) Schmidt RA, Jonas U, Oleson KA, Janknegt R, Hassouna M, Siegel S, Van Kerrebroeck P. Sacral nerve stimulation for treatment of refractory urinary urge incontinence. J Urol 1999; 162:352-357. 3) National Guideline Clearinghouse. General Treatment of Chronic Pelvic Pain. Accessed 4/8/10. http://www.guideline.gov/summary/summary.aspx?doc_id=12612 4) Maher CF, Carey MP, Dwyer PL, Schluter PL. Percutaneous sacral nerve root neuromodulation for intractable interstitial cystitis. J Urol. 2001 Mar;165(3):884-6. 5) Feler CA, Whitworth LA, Fernandez J. Sacral neuromodulation for chronic pain conditions. Anesthesiol Clin N Am 2003; 21:785-95. 6) Alo KM, Yland MJ, Redko V, Feler C, Naumann C. Lumbar and sacral nerve root stimulation (NRS) in the treatment of chronic pain: A novel anatomic approach and neuro stimulation technique. Neuromodulation. 1999;2:23-31. 7) Pettit PD, Thompson JR, Chen AH. Sacral neuromodulation: New applications in the treatment of female pelvic floor dysfunction. Curr Opin Obstet Gynecol 2002; 14:521-525. 8) Siegel SW, et al. Long-term results of a multicenter study on sacral nerve stimulation for treatment of urinary urge incontinence, urgency-frequency, and retention. Urology. 2000 Dec 4;56(6 Suppl 1):87-91. 9) Peters KM, Konstandt D. Sacral neuromodulation decreases narcotic requirements in refractory interstitial cystitis. BJU Int 2004:Apr93(6):777-9. 10) Falletto E, Masin A, Lolli P, Villani R, Ganio E, Ripetti V, Infantino A, Stazi. Is sacral nerve stimulation an effective treatment for chronic idiopathic anal pain? Dis Colon Rectum. 2009 Mar;52(3):456-62. 11) McJunkin TL, Wuollet AL, Lynch PJ. Sacral nerve stimulation as a treatment modality for intractable neuropathic testicular pain. Pain Physician. 2009 Nov-Dec;12(6):991-5. 12) Paszkiewicz EJ, Siegal SW, Kirkpatrick C, Hinkel B, Keeisha J, Kirkemo A. Sacral nerve stimulation in patients with chronic, intractable pelvic pain. Urology 2001;57(Suppl 1):124. 13) Carey M, Fynes M, Murray C, Maher C. Sacral nerve root stimulation for lower urinary tract dysfunction: overcoming the problem of lead migration. BJU 2001; 87(1):15 –
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