Peripheral and Central Contributions to Hyperalgesia in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder seen by gastroenterologists. We discuss some recent evidence for potential neural mechanisms that could contribute to somatic and visceral hyperalgesia in IBS patients. The combination of research studies of human IBS patients and studies of rats with delayed rectal hypersensitivity after recovery from experimentally induced neonatal colitis strongly suggests a mechanism wherein both primary visceral hyperalgesia and secondary widespread cutaneous hyperalgesia are dynamically maintained by tonic impulse input from the noninflamed colon and/or rectum. The secondary hyperalgesia is likely to be at least partly related to sensitization of spinal cord dorsal horn neurons and in this respect might be similar to other persistent pain conditions such as fibromyalgia and complex regional pain syndrome. Perspective: Pain in irritable bowel syndrome is likely to be at least partly maintained by peripheral impulse input from the colon/rectum and central sensitization, yet it is also highly modifiable by psychological factors such as nocebo and placebo effects. A synergistic interaction might occur between psychological factors and abnormal afferent processing.