Sensitivity and distensibility of the rectum and sigmoid colon in patientswith irritable bowel syndrome

Background: Hyperalgesia to visceral stimuli is a biological marker of the irritable bowel syndrome (IBS). Abnormal pain processing is probably of mos t importance, but biomechanical abnormalities of the gut wall may also cont ribute to the findings. In the current study, we investigated the sensation of the gut to electrical stimuli as well as the distensibility of the rect um and sigmoid colon in IBS patients and a control group. Methods: Nine pat ients with IBS and 11 controls entered the study. The pain threshold to ele ctrical stimuli at the rectosigmoid junction was determined with bipolar el ectrodes integrated on the biopsy forceps for the endoscope. Subsequently, controlled distensions of the sigmoid colon and rectum were performed with a balloon integrated on a probe for impedance planimetry, providing the pos sibility to measure the cross-sectional area (CSA), wall tension and strain to different pressures together with the sensation ratings. Results: The p ain detection thresholds to electrical stimuli at the rectosigmoid junction were 12.5 (range 7-39) mA in controls and 7.5 (range 0.75-12) mA in IBS pa tients (P = 0.03). The calculated pressures at the pain detection threshold in the sigmoid colon were lower in the IBS patients (31.5 (range 5-58) ver sus 5 cm (range 5-25) water; P = 0.03), otherwise no differences were seen in sensation rating to the: different distension pressures. The CSA was sli ghtly higher in controls to the different pressures, whereas no differences between the groups were seen in strain and tension of the rectum and sigmo id colon. Conclusion: The visceral hypersensitivity in IBS seems to be rela ted to alterations in the nervous system rather than biomechanical paramete rs such as the tension and strain of the gut wall. Treatment of pain in IBS should therefore be based on drugs with documented action on the nocicepti ve pathways in the central nervous system.