Can sensory and/or motor reactions during percutaneous nerve evaluation predict outcome of sacral nerve modulation?

A major advantage of sacral nerve modulation in the treatment of fecal incontinence is the ability to determine the likely treatment outcome before implantation by means of a percutaneous nerve evaluation and a test stimulation period. This study evaluated the predictive value of both sensory and motor responses during percutaneous nerve evaluation for determining the outcome of subchronic test stimulation and permanent stimulation.

All percutaneous nerve evaluation procedures performed between 2000 and 2007 were analyzed. Two hundred eight procedures (194 females; mean age, 56.7 years) were included in this study. Correct needle placement was confirmed by typical S-3 sensory and/or motor responses. The sensory and motor responses during the procedure were analyzed in relation to the outcomes of the test stimulation and permanent stimulation.

In all, 72.6% of patients had a successful subchronic test stimulation. A total of 13.9% had no motor response. There was no significant difference in outcome between the group with only sensory responses and the group with both sensory and motor responses (P = 0.89; odds ratio, 1.01; 95% confidence interval, 0.42-2.43). Correlation with permanent implantation showed no significant difference between both groups in outcome (P = 0.53; odds ratio, 0.48; 95% confidence interval, 0.17-1.41).

Positive motor responses during percutaneous nerve evaluation are highly predictive of a successful outcome of subchronic test stimulation and permanent sacral nerve modulation. Sensory responses also have the same predictive value. For this reason, percutaneous nerve evaluation preferably should be performed in awake patients under local anesthesia to avoid missing those who may benefit from permanent stimulation but who do not have a motor response during the procedure.