Reliability of electrophysiologic anal tests in predicting the outcome of sacral nerve modulation for fecal incontinence

INTRODUCTION: Sacral nerve modulation has been demonstrated to be a new efficacious treatment for fecal incontinence. The effectiveness of the procedure is preliminarily tested by means of a peripheral nerve evaluation. Integrity of the sacral neural pathway is generally believed to be a necessary condition for a good response, but no data are available to confirm whether electrophysiologic anal tests are predictive of the clinical outcome of the peripheral nerve evaluation. METHODS: Eighty-two incontinent patients underwent the peripheral nerve evaluation after full evaluation of the anorectal physiology. Univariate analysis was performed, and the positive predictive value, sensitivity, and specificity were calculated for each of the tests. RESULTS: Forty-six patients had successful results to the peripheral nerve evaluation and were subjected to permanent implant of a sacral electrostimulator. Anal sphincter electromyography had been performed in 60 patients, whereas pudendal nerve terminal motor latency had been assessed in 68 and evoked sacral potentials in 29 patients. Anal electromyography was statistically related to the outcome of the peripheral nerve evaluation (P = 0.0004) with a positive predictive value of 81 percent, a sensitivity of 44 percent, and a specificity of 81 percent. Pudendal nerve terminal motor latency on the right side did not correlate with the outcome, but left pudendal nerve terminal motor latency was weakly correlated (P = 0.02), although both tests had a low positive predicting value and sensitivity vs. good specificity. Evoked sacral potentials did not correlate with the outcome and had a low positive predictive value, sensitivity, and specificity. CONCLUSIONS: Simple anal sphincter electromyography can predict the outcome of the peripheral nerve evaluation with good positive predictive value and specificity in patients with fecal incontinence. Other, more expensive, electrophysiologic anal tests do not add further prognostic information.