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interstim therapy for urinary incontinence

by Diane K. Newman, DNP, FAAN, BCB-PMD

InterStim® Therapy, sometimes referred to as sacral neuromodulation therapy, is a reversible treatment that uses mild electrical pulses (called electrical stimulation) to stimulate nerves in your lower back, just above the tailbone. These nerves are called sacral nerves. The sacral nerves (specifically S2, S3 and S4) activate or inhibit muscles and organs that contribute to urinary control -- the bladder, sphincter and pelvic floor muscles.



Specifically, S3 influences pelvic floor behavior. The electrical stimulation artificially excites nerve pathways that may activate or inhibit muscle action, depending on their normal function. Electrical stimulation can stimulate somatic nerve fibers without causing simultaneous contractions of the bladder. This may decrease the urinary incontinence symptoms of urgency, frequency, urinary retention and urge incontinence.

The InterStim® treatment is a solid step in the treatment of urge incontinence, urgency, frequency and urinary retention. It is contraindicated (should not be used) in a person who has not demonstrated an appropriate response to test stimulation or is unable to operate the neurostimulator. In addition, the use of diathermy (the production of heat in body tissues for therapeutic effect) is contraindicated after implantation of any InterStim® products. InterStim® Therapy is not intended for patients with mechanical obstruction of the urethra (urethral stricture, cancer or benign prostatic hypertrophy, for examples).

Who is the best person to receive the InterStim® Therapy treatment?

Many people have chronic, debilitating symptoms of voiding dysfunction that are refractory (do not respond) to standard treatments. Refractory voiding dysfunction is often under-acknowledged, may affect a large number of people and has been proven to be difficult to treat. This type of bladder dysfunction can have a debilitating impact on a person's social and personal life, so effective therapy carries great potential for life-changing benefits.

Usually these persons suffer from overactive bladder (OAB) symptoms, which include urge incontinence, urgency, frequency (referred to as urgency/frequency syndrome) or urinary retention. These symptoms are defined as follows:

  • Urge incontinence: The involuntary and accidental loss of urine when the person is aware of the need to get to the bathroom but is not able to hold or suppress the urge long enough to get there. Usually it is accompanied by or immediately preceded by urgency.
  • Urgency: A strong, intense and often sudden desire to void. Urgency, with or without urge incontinence, usually with frequency and nocturia (nighttime urination), can be described as the overactive bladder (OAB) syndrome, urge syndrome or urgency-frequency syndrome.
  • Frequency: voiding more than eight times in a 24-hour period. People report that the urgency is so great they need to rush to the bathroom frequently. When they void, it is usually in small amounts.
  • Urinary retention is the inability or failure to completely empty the bladder. The way to determine if you have urinary retention is for a physician to get a post-void residual (PVR). A PVR is done by inserting a catheter into your bladder or by an ultrasound of your bladder. It is done 5 to 10 minutes after you urinate. If the volume is greater than 100cc's (3 oz) then you may have urinary retention. Persons with urinary retention usually only void small amounts of urine. They may also experience urine leakage called overflow incontinence. Usually in order to completely empty the bladder these persons have to insert a catheter 3 or 4 times a day to drain the urine from the bladder.

In refractory voiding dysfunction (urinary dysfunction that does not respond to standard treatments), urine loss occurs when the detrusor (bladder) muscle of the bladder wall involuntarily contracts during bladder filling, forcing urine through the urethra. Ordinarily, when a person feels the urge to urinate, a bladder contraction can be inhibited through brain control or contraction of the pelvic floor muscles. Bladder contractions are normally stimulated through the voiding reflex that is found in the sacral nerve segments as described above.

People suffering from refractory bladder overactivity typically have to empty their bladders frequently and when they experience a sensation of urgency, may leak urine if they are unable to reach the toilet quickly or if the sensation of urgency is very strong. The amount of urine lost may be large (greater than 100 ml), as the bladder may empty completely and involuntarily. The volume of urine lost with accidents varies tremendously and does not seem dependent on bladder volume. Persons will complain that the urine just "gushes" out. Sleep may be disturbed, as the need to void may awaken the person three or more times per night.

Causes of refractory voiding dysfunction include childbirth, prior pelvic surgery (hysterectomy), repeated urinary tract infections or bladder tumors which can cause bladder irritation leading to urge urinary incontinence.

How effective is InterStim® Therapy?

There are many published reports on the successful outcome of this treatment in both men and women. One of the earliest studies by Schmidt et al (1999) studied 76 patients and reported that at twelve months, 79 percent of people with urge incontinence had a 50 percent reduction in frequency of incontinent episodes with 45 percent of these patients saying that they were completely dry. Jonas (2001) studied 24 patients with urinary retention and found at eighteen months after implant, 14 (58 percent) no longer needed to perform catheterization and three (13 percent) had a 50 percent or greater reduction in the amount of urine catheterized (drained) from the bladder. There are many more studies that document the outcomes of InterStim® Therapy and references are included.

What is the actual InterStim® procedure?

The InterStim® procedure is done in two steps or stages. This allows your physician to test the therapy before actually performing the procedure!

Step 1 is to decide if this treatment will improve your symptoms. Before Step 1 you will have to keep a Bladder Record at least for a week to establish a baseline record of your symptoms for comparison after the test stimulation.

Step 1 - Test Stimulation in Preparation for InterStim® procedure

A test (the temporary test stimulation) is used before implantation of the InterStim® neurostimulator to see what the effect of stimulation is on your symptoms. This is usually performed in your physician's office and can be done as an outpatient procedure. It usually takes twenty to thirty minutes. You will need to lay face down on an examination table.

You will receive a local anesthetic into your skin (usually lidocaine) so the area where the surgeon will work is numb. The physician will push on your lower back to identify the area to place the test lead (a thin, insulated wire with electrodes at the tip). The test stimulation procedure involves insertion of a needle and lead near the sacral foramen (appropriate sacral nerve which is in the lower back) on the left or right side.


Stimulation is applied and the person will be asked to identify the location of the sensation: the vagina, scrotum, bladder or rectum. Usually the stimulation sensation is a vibration or pulling sensation in the vagina or rectum. Once the person feels the sensation then the physician will monitor the anus (opening to the rectum) or toes. Tightening of the anus or flexing of the great toe will occur if the appropriate sacral nerve is being stimulated.

Once the response is confirmed, a lead wire is threaded through the needle and the needle is removed leaving the temporary lead wire in place. The lead is connected to a screener cable; one cable is connected to the lead in the back and the other to a ground pad. The lead in the back is connected to an external stimulation device (See Figure 5). X-rays are usually taken to confirm the position of the lead. The external stimulator unit should be left on 24 hours per day. The test period can be for three to seven days and you can adjust the stimulation settings. While you have the test stimulator in place you should limit some of your activities (no lifting, sexual intercourse, showers, or baths, for examples).

You will need to record your symptoms using Bladder Records (See sample form below.) If your symptoms improve by at least 50 percent (decrease in urgency, frequency or incontinence) or disappear during the test period, long-term use of InterStim® Therapy may be appropriate for you and you may proceed to Step 2. In persons with urinary retention, success with Step 1 would be the ability to void without catheterization or at least a 50% reduction in residual volume. In some cases the test stimulation may not be conclusive and your physician may suggest repeating the procedure. Your physician may repeat the procedure using the same technique described above, or he may recommend a "staged implant." In a staged implant, the physician places the permanent lead into the sacrum and attaches it to an external stimulator. If this test is positive, the lead will stay in place and you will proceed on to step 2 outlined below. If the test is not successful, the lead will be removed.

Step 2 - The implant of the InterStim® neurostimulator

If your symptoms decrease by at least 50 percent and you are pleased with the test results, you can receive the implantable InterStim® system. The actual InterStim® unit is implanted in the sacral nerve and usually requires a one-night stay in the hospital. The following are the general steps in the surgery for the placement of the permanent internal battery (IPG) implant or Step 2 of the InterStim® System. Your physician's method may be different from what is described here.

Before undergoing Step 2, you will need to have a history and physical examination, routine blood tests, a chest x-ray, urine culture and an EKG (cardiogram) if you have a history of heart problems. You will not be able to eat or drink anything after midnight on the day before the surgery.

To place an InterStim® System, an operation is performed under general anesthesia. Therefore, you will be asleep during the procedure. An incision (cut) is made over your sacral area (lower back) and a lead (a thin wire with small electrodes at its tip) is placed near the appropriate sacral nerve (1 to 1.5 inches deep) that controls urinary function. (Those who receive a "staged implant," as outlined in Step 1 above, will not undergo this portion of the procedure, as the lead would have already been placed for the test stimulation.)The lead and an extension wire that is attached to the lead are passed under the skin to a small neurostimulator (approximately the size of a stopwatch) that is placed in a "pocket" just under the skin on the upper part of your buttock. The neurostimulator contains a special battery.

The physician uses a programmer to set stimulation settings and to check neurostimulator information. Settings include voltage output amplitude, pulse width, rate, polarity and stimulation mode. The person is given a hand-held programmer with replaceable battery to turn the stimulator on and off and to adjust or fine-tune the voltage output amplitude as needed. The system may not be turned on for several (around seven to ten) days after the procedure. You and your physician or the nurse will adjust the stimulation settings to maintain the most effective control of your symptoms without discomfort. You may need to make several visits to fine-tune the settings that are best for you. You can adjust the stimulator by using the knobs on the unit to slowly increase or decrease the intensity. The neurostimulator typically runs for 5-10 years. However, depending on the person's usage requirements, it could be less than 5 years. When the battery runs out, the neurostimulator will need to be replaced, typically during an outpatient procedure.

What problems can occur with InterStim® treatment?

As with any surgery, problems can occur. You can get an infection at the site but you your physician may prescribe antibiotics at the time of the implant surgery and for ten to fourteen days after the implant. Look at the site of the surgery for any swelling or redness, which are signs of an infection. Call your physician if your have a fever or notice drainage from the site of the operation. In addition to surgical risks, problems with the system could occur. The lead may become dislodged or move away from the nerve. If this occurs, InterStim® Therapy may lose effectiveness and may require surgery to reposition or replace the lead. You may experience light shocks and swelling. Pain can occur at the stimulation/implant site and/or lead site. In the initial study conducted in the mid 1990s, there was a 33 percent revision rate, which means that additional surgeries may be required because of technical failure of the implanted unit. If a woman with the stimulator in place becomes pregnant, the unit should be deactivated and a cesarean delivery may be considered.

Will my insurance cover InterStim® Therapy?

Probably yes, as most major private insurers are covering this treatment. Medicare will cover sacral nerve stimulation for the treatment of urinary urge incontinence, urgency-frequency syndrome and urinary retention if the following criteria are met:

  • Documented failure to conventional therapy (drug, behavioral)
  • Persons with stress urinary incontinence, urinary obstruction and specific neurological diseases (diabetes with nerve involvement) that are associated with secondary manifestations of the above three indications are excluded.
  • Person must have a successful test stimulation (Step 1) or a successful staged lead implant in order to support implantation and the person must demonstrate a 50 percent or greater improvement in Step 1 as measured through Bladder Records.
  • Person must be able to complete Bladder Record data so that implant procedure outcome can be evaluated.

What should I do if I think I may be a candidate for the InterStim® Therapy?

If you would like more information about InterStim® Therapy, or if you think you might be a candidate for this therapy, talk with your urologist or urogynecologist. You may also receive additional information about InterStim® Therapy directly from Medtronic. Medtronic, the company that manufacturers the InterStim® system, trains all physicians before they can provide this therapy. The company has a list of trained physicians on its website, located at


Posted July 2002
Updated May 2009


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