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Overactive Bladder: an Evaluation of Interstim Outcomes

R. Corey O'Connor, MD, Associate Professor
Michael Guralnick, MD, Associate Professor

Overactive bladder (OAB) is a common, chronic condition that affects about 37 million adults in the United States.1 Symptoms of OAB include urinary urgency and frequency with or without incontinence. Standard initial treatments include behavioral modification and  anticholinergic/antimuscarinic medications. Unfortunately, a significant number of patients do not improve with these  therapies or do not tolerate the drug side effects.

Over the past decade, sacral neuromodulation has become an accepted modality for the treatment of OAB symptoms refractory of behavioral and drug therapy. While the exact mechanism of action remains unclear, most theories involve the modulation of afferent  and/or efferent neural pathways of the bladder.2

Common  practice involves placing the sacral neuromodulator in the operating room during two staged outpatient procedures. Stage I entails the percutaneous insertion of a quadripolar tined lead into the right or left third sacral foramina under fluoroscopic guidance.3   A trial period of lead stimulation via an external power source is then conducted for one to two weeks to assess efficacy.  Stage II involves the subcutaneous  placement of an implantable pulse generator (battery) in the patient’s upper buttock, which is connected to the previously placed  tined lead. Progression from stage I to stage II is warranted if the patient experiences a 50 percent or greater improvement in OAB symptoms during the trial stimulation period.

We hypothesized that the placement of bilateral leads during stage I implantation would improve the chances of a successful trial. Between 2004 and 2009, we placed 56 unilateral and 71 bilateral stage I S3 leads in patients with refractory OAB symptoms. Successful outcomes were noted in 61 percent of unilateral and 83 percent of bilaterally placed leads (p < 0.05) (Figure 1). Due to the statistically significant improvement in outcomes following bilateral lead placement, we recommend this technique for all of our patients who elect to undergo sacral neuromodulator implantation.4

In 2010, we began to replace bilateral stage I implantations with bilateral percutaneous nerve evaluation (PNE) testing. Unlike the traditional intraoperative stage I procedure, PNE involves the percutaneous placement of temporary bilateral S3 leads during a 10 minute office procedure. The leads are tested over a four day trial period. Patients reporting a 50 percent or greater improvement in OAB symptoms then undergo a single intraoperative procedure to implant a permanent S3 lead and subcutaneous battery. Advantages of PNE testing as opposed to traditional intraoperative lead placement include less procedural time, less patient discomfort, a shorter trial period and possibly, a lower risk of device infection. To date, 19 patients have undergone PNE testing. Overall progression to permanent implantation (e.g., success) is 84 percent. When compared to traditional staged bilateral sacral neuromodulator implantation, bilateral PNE testing is quicker, easier for the patient and physician and offers similar success rates to traditional lead placement. Patients who fail PNE testing are offered a traditional staged implantation to determine if their OAB symptoms can be improved with sacral neuromodulation. 




  1. Stewart WF, Van Rooyen JB, Cundiff GW, et al. Prevalence and burden of overactive bladder in the United States. World J Urol. 2003;20:327-336.
  2. Hijaz A, Vasavada S, Rackley R. Sacral neuromodulation - State-of-the-art strategies and troubleshooting techniques. Contemp Urol 2006;2:26-37.
  3. Janknegt RA, Weil EH, Eerdmans PH. Improving neuromodulation technique for refractory voiding dysfunctions: two-stage implant. Urology 1997;49:358-62.
  4. Pham K, Guralnick ML, O’Connor RC. Unilateral versus bilateral stage I neuromodulator lead placement for the treatment of refractory voiding dysfunction. Neurourol Urodyn. 2008;27:779-81. 


© 2014 Medical College of Wisconsin
Page Updated 12/12/2013