irritable bowel syndrome
Meaning of irritable bowel syndrome: Normal test results form part of the picture rather than evidence that nothing is wrong, which is the point most often misread.
Definition of irritable bowel syndrome
Irritable bowel syndrome is a long-term disorder in which abdominal pain occurs together with a change in bowel habit, without structural damage to the bowel that tests can detect. The pain is linked to opening the bowels and to a shift toward looser or harder stool. The gut and the nerves serving it are working abnormally rather than being damaged.
What is wrong if the bowel looks normal?
The fault lies in how the gut and the nervous system communicate rather than in the tissue itself. Three findings recur. Nerves carrying sensation from the bowel are set at a lower threshold, so ordinary amounts of gas and stretch register as pain, an effect called visceral hypersensitivity. The muscle contractions moving contents along run too fast or too slow, giving diarrhea or hard stool. Signaling between gut and brain is altered in both directions, which is why stress reliably worsens symptoms and why gut symptoms in turn affect mood. A substantial share of cases begin after an episode of gastroenteritis, and changes in the bacterial population of the colon and in the permeability of its lining have both been described.
What are the subtypes?
| Subtype | Predominant stool pattern |
|---|---|
| Diarrhea predominant | Mostly loose or watery |
| Constipation predominant | Mostly hard or lumpy |
| Mixed | Both, alternating |
| Unclassified | Neither pattern dominant |
The subtype often shifts over the years within the same person, which is one reason the condition is described by its current pattern rather than fixed at the point of diagnosis.
How is it separated from inflammatory bowel disease?
Both cause abdominal pain and altered bowel habit, and the names sit close enough to be mistaken for one another, but the underlying state differs. Crohn disease and ulcerative colitis physically damage the bowel wall, produce ulcers visible at endoscopy, raise inflammatory markers in blood and stool, and can lead to bleeding, narrowing and surgery. Irritable bowel syndrome does none of that. Features lying outside the syndrome include blood in the stool, fever, unintended weight loss, anemia, symptoms waking a person from sleep, and a first appearance in later adult life. Their presence directs assessment elsewhere, because they are not part of it.
Also known as
Used in a sentence
The abdominal pain and alternating bowel habit were attributed to irritable bowel syndrome.
Good to know
Irritable bowel syndrome is recognized by the pattern of symptoms rather than applied as a label when tests find nothing, and features such as bleeding, fever, anemia, weight loss or symptoms waking a person from sleep fall outside the syndrome and point elsewhere.