Overview
Irritable bowel syndrome (IBS) is a functional GI disorder characterized by abdominal pain and altered bowel habits in the absence of specific and unique organic pathology. Osler coined the term mucous colitis in 1892 when he wrote of a disorder of mucorrhea and abdominal colic with a high incidence in patients with coincident psychopathology. Since that time, the syndrome has been referred to by sundry terms, including spastic colon, irritable colon, and nervous colon.
Traditionally, irritable bowel syndrome is a diagnosis of exclusion. No specific motility or structural correlates have been consistently demonstrated, so irritable bowel syndrome remains a clinically defined illness.
Manning and associates established 6 criteria to distinguish irritable bowel syndrome from organic bowel disease.1 Although historically important, these criteria are insensitive (58%), nonspecific (74%), and less reliable in men. The Manning criteria to distinguish irritable bowel syndrome from organic disease are as follows:
•Onset of pain associated with more frequent bowel movements
•Onset of pain associated with looser bowel movements
•Pain relieved by defecation
•Visible abdominal bloating
•Subjective sensation of incomplete evacuation more than 25% of the time
•Mucorrhea more than 25% of the time
More recently, a consensus panel created and then updated the Rome criteria to provide a standardized diagnosis for research and clinical practice. The Rome III criteria (2006) for the diagnosis of irritable bowel syndrome require that patients must have recurrent abdominal pain or discomfort at least 3 days per month during the previous 3 months that is associated with 2 or more of the following:
•Relieved by defecation
•Onset associated with a change in stool frequency
•Onset associated with a change in stool form or appearance
Supporting symptoms include the following:
•Altered stool frequency
•Altered stool form
•Altered stool passage (straining and/or urgency)
•Mucorrhea
•Abdominal bloating or subjective distention
Four bowel patterns may be seen with irritable bowel syndrome. These patterns include IBS-D (diarrhea predominant), IBS-C (constipation predominant), IBS-M (mixed diarrhea and constipation), and IBS-A (alternating diarrhea and constipation). The usefulness of these subtypes is debatable. Notably, within 1 year, 75% of patients change subtypes, and 29% switch between constipation-predominant IBS and diarrhea-predominant IBS.
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