Background: Hyperalgesia to visceral stimuli is a biological marker of the irritable bowel syndrome (IBS). Abnormal pain processing is probably of most importance, but biomechanical abnormalities of the gut wall may also contribute to the findings. In the current study, we investigated the sensation of the gut to electrical stimuli as well as the distensibility of the rectum and sigmoid colon in IBS patients and a control group.
Methods: Nine patients with IBS and 11 controls entered the study. The pain threshold to electrical stimuli at the rectosigmoid junction was determined with bipolar electrodes 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 possibility to measure the cross-sectional area (CSA), wall tension and strain to different pressures together with the sensation ratings.
Results: The pain 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 patients (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) versus 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 slightly higher in controls to the different pressures, whereas no differences between the groups were seen in strain and tension of the rectum and sigmoid colon.
Conclusion: The visceral hypersensitivity in IBS seems to be related to alterations in the nervous system rather than biomechanical parameters 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 nociceptive pathways in the central nervous system.