Physiologic determinants of nocturnal incontinence after ileal pouch-anal anastomosis

The goals of the ileal pouch-anal anastomosis (IPAA) operation are the construction of a fecal reservoir and the preservation of anal function, without compromising continence. Some of the patients are incontinent at night. The aim of our study was to identify the mechanisms responsible for nocturnal incontinence. We analyzed patients undergoing IPAA for ulcerative colitis, who underwent anorectal tests between 1993 and 1995. All patients were subjected to pull-through manometry and pelvic floor function studies, and 33 patients underwent overnight ambulatory manometry. Among 44 patients (27 men and 17 women), 22 had complete continence, whereas 22 had nocturnal incontinence. Mean age was 40 +/- 1 years. There were no differences with regard to sex, age, stool consistency, and ability to differentiate gas from stool between groups; only stool frequency was lower in the continent group (median [range] 6 [3 to 10] vs. 8 [5 to 25] stools/24 hours; P = 0.011). Resting and squeezing anal canal pressure did not differ (P = 0.42 and P = 0.73, respectively). Resting, squeezing, and defecating anorectal angle, percentage of pouch evacuation, and perineal descent, all measured scintigraphically, did not differ between groups (all P >0.05). Ambulatory manometry showed that the mean anal canal pressure was higher in continent patients compared to incontinent patients, both during awake (88 +/- 11 vs. 62 +/- 8; P = 0.032) and sleep (81 +/- 14 vs. 49 +/- 9; P = 0.029) periods. The motility index was similar (awake, P = 0.88; sleep, P = 0.95), as was the number of episodes where the pouch pressure was greater than the anal canal pressure (P = 0.28). In otherwise continent patients after IPAA, the combination of high stool frequency and low basal anal canal pressure may be related to nocturnal incontinence. Moreover, standard anorectal physiology tests cannot identify these subtle differences.