The Utility of Pudendal Nerve Terminal Motor Latencies in Idiopathic Incontinence

PURPOSE: Pudendal nerve terminal motor latency testing has been used to test for pudendal neuropathy, but its value remains controversial. We sought to clarify the relationship of pudendal nerve terminal motor latency to sphincter pressure and level of continence in a cohort of patients with intact anal sphincters and normal pelvic floor anatomy. METHODS: We reviewed 1,404 consecutive patients who were evaluated at our pelvic floor laboratory for fecal incontinence. From this group, 83 patients had intact anal sphincters on ultrasound and did not have internal or external rectal prolapse during defecography. These patients were evaluated by pudendal nerve terminal motor latency testing, a standardized questionnaire, and anorectal manometry, which measured resting and squeeze anal pressures. Incontinence scores were calculated by using the American Medical Systems Fecal Incontinence Score. Values were compared by using the Fisher's exact test and Wilcoxon's rank-sum test; and significance was assigned at the P < 0.05 level. RESULTS: 1) Using a 2.2-ms threshold, 28 percent of patients had prolonged pudendal nerve terminal motor latency unilaterally and 12 percent bilaterally. 2) At a 2.4-ms threshold, 18 percent of patients had prolonged pudendal nerve terminal motor latency unilaterally and 8 percent bilaterally. 3) Bilaterally prolonged pudendal nerve terminal motor latency was significantly associated with decreased maximum mean resting pressure and increased Fecal Incontinence Score, but not decreased maximum mean squeeze pressure, at both 2.2-ms and 2.4-ms thresholds. 4) Unilaterally prolonged pudendal nerve terminal motor latency was not associated with maximum mean resting pressure, maximum mean squeeze pressure, or fecal incontinence score at either threshold. CONCLUSIONS: The majority of incontinent patients with intact sphincters have normal pudendal nerve terminal motor latency. Bilaterally but not unilaterally prolonged pudendal nerve terminal motor latency is associated with poorer function and physiology in the incontinent patient with an intact sphincter.