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\r\nefficacious treatment for fecal incontinence. The effectiveness of the procedure\r\nis preliminarily tested by means of a peripheral nerve evaluation. Integrity of\r\nthe sacral neural pathway is generally believed to be a necessary condition for\r\na good response, but no data are available to confirm whether electrophysiologic\r\nanal tests are predictive of the clinical outcome of the peripheral nerve\r\nevaluation. METHODS: Eighty-two incontinent patients underwent the peripheral\r\nnerve evaluation after full evaluation of the anorectal physiology. Univariate\r\nanalysis was performed, and the positive predictive value, sensitivity, and\r\nspecificity were calculated for each of the tests. RESULTS: Forty-six patients\r\nhad successful results to the peripheral nerve evaluation and were subjected to\r\npermanent implant of a sacral electrostimulator. Anal sphincter electromyography\r\nhad been performed in 60 patients, whereas pudendal nerve terminal motor latency\r\nhad been assessed in 68 and evoked sacral potentials in 29 patients. Anal\r\nelectromyography was statistically related to the outcome of the peripheral\r\nnerve evaluation ( P = 0.0004) with a positive predictive value of 81 percent, a\r\nsensitivity of 44 percent, and a specificity of 81 percent. Pudendal nerve\r\nterminal motor latency on the right side did not correlate with the outcome, but\r\nleft pudendal nerve terminal motor latency was weakly correlated ( P = 0.02),\r\nalthough both tests had a low positive predicting value and sensitivity vs. good\r\nspecificity. Evoked sacral potentials did not correlate with the outcome and had\r\na low positive predictive value, sensitivity, and specificity. CONCLUSIONS:\r\nSimple anal sphincter electromyography can predict the outcome of the peripheral\r\nnerve evaluation with good positive predictive value and specificity in patients\r\nwith fecal incontinence. Other, more expensive, electrophysiologic anal tests do\r\nnot add further prognostic information.