RECTAL AFFERENT FUNCTION IN PATIENTS WITH INFLAMMATORY AND FUNCTIONALINTESTINAL DISORDERS

Chronic symptoms of abdominal pain and discomfort are reported by pati ents with inflammatory bowel disease (IBD) and functional disorders of the gut, such as Irritable Bowel Syndrome (IBS). It has recently been suggested that transient inflammatory mucosal events may result in lo ng-lasting sensitization of visceral afferent pathways. To determine t he effect of recurring intestinal tissue irritation on lumbosacral aff erent pathways, and to identify a plausible mechanism that could accou nt for the overlap in symptomatology between IBD and IBS, we compared rectal afferent mechanisms in patients with Crohn's disease (inflammat ion limited to the ileum) with those observed in patients with diarrhe a-predominant IBS. Continuous volume ramp and phasic pressure step dis tension of a rectal balloon were performed in 9 healthy male control s ubjects, 12 male patients with isolated ileal Crohn's disease and 9 ma le patients with diarrhea-predominant IBS using an electronic visceral stimulation device. The response of rectal afferents to distension wa s evaluated by measuring thresholds for the perception of physiologica l (stool) and aversive (discomfort) sensations, viscerosomatic referra l patterns, skin conductance responses, receptive relaxation, and rect oanal reflex responses. In response to slow ramp distension, threshold s for aversive sensations were significantly higher in Crohn's disease patients, but similar between the two other groups. In response to ra pid phasic distension, IBS patients reported discomfort at lower diste nsion pressures, while all other thresholds were similar between group s. Skin conductance responses to aversive distension were greatly redu ced in Crohn's disease patients while IBS patients had greater respons es when compared to normals, Changes in viscerosomatic referral patter ns and receptive relaxation rate were similar in Crohn's disease and I BS patients. These findings demonstrate that chronic ileal inflammatio n is associated with increased thresholds for discomfort and greatly d iminished systemic autonomic reflex responses. In contrast, IBS patien ts show lowered thresholds for discomfort associated with increased au tonomic responses. The findings in Crohn's patients may result from de scending bulbospinal inhibition of sacral dorsal horn neurons in respo nse to chronic intestinal tissue irritation.