Irritable bowel syndrome: A disorder of abnormal brain-gut interactions

Irritable bowel syndrome (IBS) is defined as one of functional gastrointestinal disorders characterized by sustained abdominal pain and/or abdominal discomfort in association with abnormal bowel habituation, i.e., diarrhea and/or constipation. Most of IBS patients have dysmotility of the colon and the small intestine, visceral hyperalgesia, and/or psychological deviation. These pathophysiological phenomena had been investigated independently. However, recent progression in IBS research clarified that IBS is a disorder of brain-gut interactions. (a) In most of IBS patients, psychosocial stress induces or aggravates IBS symptoms. (b) Treatments for psychological deviation with psychopharmacotherapy or psychotherapy often improve gastrointestinal symptoms in IBS patients. (c) Visceral stimulation induces changes in neurotransmission in the brain as well as reflex changes in gastrointestinal motility. (d) IBS patients do not have somatic hyperalgesia but have visceral hyperalgesia. (e) Prospective study on acute enterocolitis revealed that patients who originally had psychological deviation developed IBS several months later. (f) IBS patients show exaggerated response of colonic motility and plasma adrenocorticotropic hormone secretion to intravenous administration of corticotropin-releasing hormone. These data suggest that IBS is a disorder of brain-gut interactions and that IBS patients have exaggerated reactivity in the brain and the gut to multiple physiological stimuli including psychosocial stress. Substance and gene regulating the vicious cycle of brain-gut link will be a key factor solving IBS, the prevalent and often intractable disorder.