Sacral Root Neurostimulation

Sacral root neurostimulation offers an alternative mode of treatment for patients with nonobstructive urinary retention. The device was approved by the United States Food and Drug Administration in 1999 for management of chronic urinary retention and frequency/urgency syndrome. Several theories about the mechanism of action have been proposed but it remains uncertain.

Initially, patients undergo percutaneous nerve evaluation (PNE) by the placement of a unilateral percutaneous lead in the S3 foramen. The lead is connected to an external pulse generator and worn by the patient for several weeks. Changes in symptoms and postvoid residuals are recorded in a detailed voiding diary. If improvement is minimal or absent, revision or bilateral percutaneous lead placement can be attempted. If greater than 50% improvement in symptoms is attained, a permanent pulse generator is implanted.

Sacral neuromodulation has been successful in patients with idiopathic nonobstructive retention, retention secondary to deafferentation of the bladder after hysterectomy, and in patients with Fowler's syndrome. Patient factors predicative of success have been sought. In 2003, Bross et al.7 evaluated the predicative ability of the carba-chol test and concomitant diseases in patients with an acontractile bladder. Eighteen patients were subcuta-neously injected with 0.25mg of carbachol. An increase in detrusor pressure to more than 20 cm within 20 to 30 minutes after injection was considered a positive test; however, only 33% of patients had a successful bilateral PNE, but a positive carbachol test was not predictive of success. Percutaneous nerve evaluation seemed particularly effective in patients who developed retention after hysterectomy.

A large prospective randomized multicenter trial to evaluate the efficacy of sacral nerve stimulation for urinary retention was performed by Jonas and colleagues8 in 2001. After a PNE period of 3 to 7 days, 68 patients (38% of those evaluated) with chronic urinary retention qualified for permanent implantation. Patients were randomly assigned to the treatment or control group in which treatment was delayed for 6 months. Successful results were initially achieved in 83% of patients who received the implant with 69% able to discontinue intermittent catheterization completely. At 18 months, 71% of patients available for follow-up had sustained improvement.

In 2002, Aboseif9 and colleagues evaluated the efficacy and change in quality of life in patients with idiopathic, chronic nonobstructive functional urinary retention. Thirty-two patients with idiopathic retention requiring intermittent catheterization underwent PNE. Permanent implants were placed in 20 patients (17 women) who showed greater than 50% improvement in symptoms. Eighteen patients were subsequently able to void and no longer required intermittent catheterization with one patient requiring bilateral implants. Average voided volumes increased from 48 to 198mL and the PVR decreased from 315 to 60 mL. Eighteen patients reported a greater than 50% improvement in quality of life, although the questionnaire used in the study was not described. Significant score improvements in the Beck depression inventory and SF-36

after sacral root neuromodulation for retention have been demonstrated by Shaker and Hassouna in 1998.10

Overall success rates of the PNE range from 33.3% to 100%. Improvement in patients with retention may not be as rapid as in patients undergoing sacral root stimulation for other reasons. A PNE period of at least 2 to 3 weeks has been recommended. Reported complications of the procedure include pain at the implant or lead site, wound infection, seroma at the implantable pulse generator site, transient sensation of electrical shock, and skin erosion at the site of the implanted pulse generator as well as hardware problems such as insulation defects and lead fracture.

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