Introduction:

Sacral nerve root stimulation is an accepted therapeutic option for the management of refractory lower urinary tract dysfunction (1,2). Preoperative trial stimulation using a temporary electrode allows for appropriate selection of patients who will benefit from a permanent sacral neuromodulator. The ease of insertion of a trial electrode and the low morbidity associated with permanent sacral neuromodulation makes this an attractive therapeutic option (1). Peripheral nerve evaluation (PNE) is usually performed using a single wire-strand PNE lead (Medtronics USA). One of the common problems encountered with this lead during trial stimulation is migration of the lead-tip resulting in a failed trial (3,4). This may arise secondary to inadvertent migration away from the sacral nerve root with movement and frequently results in repeat electrode insertion and trial stimulation. A new PNE lead containing coiled wire-strands was developed to overcome this technical problem. This allows for lead extension during movement and may help maintain contact between the lead-tip and the sacral nerve root.

Aims: 
The aims of this study were to evaluate migration of these two PNE electrodes and the response to trial stimulation using the new lead.   

Methods:

Twelve women with symptoms of  severe sensory and or urge incontinence of  twelve months duration were prospectively recruited. Each failed to respond to medical and or physiotherapy protocols. All women underwent voiding cystometry and a diagnosis was made using ICS criteria. All patients with a diagnosis of bladder hypersensitivity at urodynamics underwent cystourethroscopy and biopsy and had macroscopic and histological evidence of interstitial cystitis. A one-week urinary diary was completed prior to and during test stimulation.  Both electrodes were used for trial stimulation, the original 041830-002 model and the new 3057 model (Medtronics, USA). Foramen needles were first placed in both  S3 foramina under local anaesthesia and a ground electrode was sited over the lateral chest wall. Accurate localisation was determined by evaluating the appropriate motor and sensory responses to electrical stimulation. Once accurate placement was achieved the electrode leads were passed down the foramen needles and coupled to a hand-held pulse generator.

Lateral sacral X-rays were performed following insertion and prior to lead removal. The distance between the lead-tip and the ventral surface of the S3 foramen was measured on each radiograph by two independent assessors. Lead migration was evaluated by comparison of the distance from the S3 foramen to the lead-tip immediately following lead insertion and prior to lead removal. The efficacy of continuous sacral nerve root stimulation was assessed over a seven-day period using the new lead. Subjective improvement in symptoms was assessed by analysis of the urinary diaries before and during therapy. A reduction of 50% or more in the mean number of incontinent episodes and or urinary frequency per day was interpreted as a positive response.

Results:

The mean patient age was  49 years (range 23-79 years). The mean duration of symptoms was 42 months (30-120 months). 7(58%) had a diagnosis of detrusor instability and 5(42%) interstitial cystitis. One connector pin lead on the PNE 3057 model became detached at the time of insertion and required replacement. There were no complications recorded during the trial period.  10(83%) patients were positive responders. There was good correlation between the distances measured by both assessors between the lead-tip and ventral surface of the S3 foramen on X ray after insertion (r= 0.88) and prior to removal (r=0.95, Pearson’s correlation test).  The mean distance migrated by the new lead was 4mm (range 2-11mm) compared to a mean migration distance of 12mm(range 10-45mm) for the old lead (p= 0.02, Wilcoxon rank sum test).

Conclusion:

The new PNE electrode described in this study is associated with a high positive response rate during trial stimulation and reduced lead migration. This new lead may help overcome the problem of determining whether a negative trial stimulation is due to lead migration or true non-response and reduce the need for bilateral lead placement or repeat test stimulation.   

References:

1.      Dijkenna HE, Weil EHJ, Mijs PT, Janknegt RA. Neuromodulation of sacral nerves for incontinence and voiding dysfunctions. Eur Urol 1993;24:72-76.

2.      Schmidt RA, Jonas U, Oleson KA, Janknegt RA, Hassouna MM, Iegel SW. Sacral nerve stimulation for treatment of refractory urinary urge incontinence. Journal of  Urology  1999;162:352-357.

3.      Bosch JL, Groen J. Sacral (S3) segmental nerve stimulation as a treatment for urge incontinence in patients with detrusor instability: results of chronic electrical stimulation using an implantable neural prosthesis. Journal of Urology 1995; 154:504-507.

4.      Tang CL, Tjandra JJ, Ooi BS, Carey M, Dwyer P. Effect of unilateral sacral nerve stimulation on anorectal function. Journal  of Pelvic Surgery 1999;5: