Sacral nerve stimulation, also termed sacral neuromodulation, involves the implantation of a programmable stimulator subcutaneously which delivers low amplitude electrical stimulation via a lead to the sacral nerve, usually accessed via the S3 foramen.
Currently, the FDA has approved InterStim Therapy, by Medtronic, as a safe sacral nerve stimulator for treatment of Urinary Urge Incontinence, Urinary Frequency, and Urinary Retention. Sacral nerve stimulation is also under investigation as treatment for a host of other conditions.

History

TENS (Transcutaneous Electrical Nerve Stimulation) was patented and first used in 1974 for pain relief. TENS is non-invasive; it sends electrical current through electrodes placed directly on the skin. However, the efficacy of TENS remains controversial as the data is inconclusive.

TENS treatment did pave the way for other types of electrical stimulation for the body, primarily sacral nerve stimulation. The first sacral nerve stimulation study was performed in 1988. By penetrating the skin, sacral nerve stimulation aims to give a direct and localized electrical current to specific nerves in order to elicit a favored response. Today it is one of the most common neuromodulation techniques.

Pre-operative testing

Patients interested in getting a sacral nerve stimulator implanted in them because less severe methods have failed all must go through a trial for their own safety, known as the PNE (percutaneous nerve evaluation). PNE involves inserting a temporary electrode to the left or right of the S3 posterior foramen. This electrode is connected to an external pulse generator, which generates a signal for 3–5 days. If this neuromodulation has positive results for the patient, the option of implanting a permanent electrode for permanent sacral neuromodulation is possible.

Implantation

One of the greatest strengths for sacral nerve stimulation is the low level of invasiveness, all incisions are relatively small. A pulse generator is implanted in a subcutaneous pocket in the upper, outer quadrant of the buttock or even the lower abdomen. The generator is attached to a thin lead wire with a small electrode tip which is anchored near the sacral nerve.

Post-operation

The most common complaints are pain and lead migration. In most studies, usually 5-10% of subjects need post-operative correction to lead migration, but since leads can be anchored near the sacral nerve, subsequent operations are generally unnecessary.

Possible mechanism

Stimulation of the sacral nerve causes contraction of external sphincter and pelvic floor muscle, which in turn causes the inhibition of bladder contractions which may be involuntarily releasing urine. Researchers currently believe that the sacral neuromodulation blocks the c-afferent fibers, which are a critical part of the afferent limb of a pathological reflex arc believed to be responsible for incontinence.

Urinary urge

Urinary urge

Urinary urgency

Urinary urgency is a sudden, compelling urge to urinate. It is often, though not necessarily, associated with urinary incontinence, polyuria, nocturia, and interstitial cystitis. It tends to increase with age...

 incontinence is a condition in which a strong urge to urinate is followed by an involuntary loss of urine. It affects around 13 million Americans, with an additional million every year. In one study, around 70% of subjects undergoing SNS showed greater than 50% improvement of symptoms of urinary urge incontinence. In another study, clinical success rates ranged from 70-90%.

Fecal incontinence

Fecal incontinence, the involuntary loss of stool, can also be treated with sacral nerve stimulation as long as patients have intact sphincter muscles. Current data is very hopeful, but to attain FDA approval for method, more long-term studies must be performed. FDA has recently approved the approach for treating the fecal incontinence as well (March 2011)

Idiopathic constipation

Sacral nerve stimulation has recently been tested to treat people with chronic idiopathic constipation. Preliminary data showed that after a year of sacral stimulation, the frequency of defecation doubled, time spent on bowel movement decreased by approximately 45%, and straining was halved in test subjects.

Urinary retention

In one case study, a woman, 38 years old, who had been sexually abused as a child became completely unable to void. She was subjected to sacral nerve stimulation and regular voiding began to take place.

Interstitial cystitis

Recent studies have shown that for patients with well-documented interstitial cystitis, pudendal stimulation, which is stimulation of the pudendal nerve, is more effective than sacral stimulation. As compared to those receiving sacral stimulation, patients receiving pudendal stimulation had fewer voids per day as well as greater voiding volume, resulting in a greater decrease in incontinence. Symptoms of other diseases, such as myelitis

Myelitis

Myelitis is a disease involving inflammation of the spinal cord, which disrupts central nervous system functions linking the brain and limbs. The name is derived from Greek referring to the "spinal cord", and the suffix -itis, which denotes inflammation....

 and Multiple sclerosis

Multiple sclerosis

Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...

, can also be greatly reduced by long-term sacral neuromodulation.

Sexual function in females

Although the main benefit of sacral nerve stimulation is urinary regularity, sacral nerve stimulation also imposes indirect benefits to people undergoing this treatment. Studies show that females who have an implanted sacral neuromodulator not only have positive effects on their continence, but also experience increased sexual desire after implantation.

Reduction of pressure ulcers

People suffering from multiple sclerosis, spinal cord lesions, or any other condition which causes them to use a wheelchair all the time have noted that sacral nerve stimulation has decreased the ischial pressure as well as increased the cutaneous hemoglobin and oxygen levels in the buttocks. This decrease in pressure and increase in circulation is thought to decrease the overall prevalence and severity of pressure ulcers that many people in wheelchairs suffer from.