CHARACTERIZATION OF AFFERENT MECHANISMS IN ILEOANAL POUCHES

Objectives: The afferent innervation of ileoanal pouches plays an impo rtant role in perception and in reflex regulation of pouch function. W e aimed to characterize afferent nerve function in ileoanal pouches an d thereby explain the clinical presentation of patients with such pouc hes. Methods: In eight patients who underwent surgery for active ulcer ative colitis, perception of balloon distention of the pouch was measu red using an electronic visceral distention device. In addition, pouch compliance and ileoanal reflex function were determined. Studies were performed during the initial stage of pouch creation (pouch without c onnection to proximal ileum, study 1) and a mean of 6.6 wk (range = 2- 12 wk) after the second stage of the surgery (proximal ileum, in conti nuity with the pouch, study 2). Nine normal volunteers made up the con trol group. Results: When expressed as intrapouch pressure, thresholds for stool and discomfort sensations were similar in patients with a p ouch and controls. However, during ramp distention, patients with a po uch had a lower volume threshold for stool sensation (143 +/- 45 ml vs 300 +/- 30 ml, p = 0.009). The initial sensation of discomfort was ex perienced in the perineum at the S3 dermatome in all eight patients. A t higher distention pressures, all patients with a pouch referred sens ations to the abdomen, as opposed to only one of nine controls with su ch a referral pattern (p < 0.0001). Pouch compliance was markedly redu ced during study 1 but normalized after continuity was established wit h the proximal ileum. Anal sphincter function in patients,vith a pouch was; similar to that in controls. Conclusions: Afferent pathways from both the ileum and rectum play a role in the mediation of sensations during mechanical distention of the ileoanal pouch and can explain a n umber of clinical features of patients with a pouch. The thresholds fo r activation of these pathways are not significantly altered by long-s tanding colorectal inflammation or by creation of the ileoanal pouch. Continuity with the proximal ileum significantly influences pouch comp liance.