For doctors, IBS can be challenging to diagnose, because tests often show no abnormalities even though symptoms are often all too real. As a result, a diagnosis of irritable bowel syndrome is usually arrived at by process of elimination, if you will excuse the pun, after other disorders with similar but more serious symptoms–such as diverticulitis, ulcerative colitis, Crohn’s disease, or intestinal parasites–have been ruled out.
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
- Altered stool frequency
- Altered stool form
- Altered stool passage (straining and/or urgency)
- Abdominal bloating or subjective distention. Four bowel patterns may be seen with irritable bowel syndrome. These patterns include
- IBS-D (diarrhoea predominant),
- IBS-C (constipation predominant),
- IBS-M (mixed diarrhea and constipation), and
- IBS-A (alternating diarrhoea 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 diarrhoea-predominant IBS.
- Abdominal pain typically occurs in the lower left abdominal quadrant, and is relieved by defecation or passage of wind
- The patient may complain of a feeling of incomplete emptying of the bowel ‘rectal dissatisfaction’
- Abdominal distension with a subjective sensation of bloating
- Anxiety or depression is often present
- Up to 20% of patients develop symptoms after a bout of infectious gastro-enteritis – ‘post infectious IBS’
While experts have suggested many potential causes for irritable bowel syndrome, no single cause has been established beyond a reasonable doubt. The list of possible culprits has ranged from parasitic infections and lactose intolerance, to food allergies and overuse of antibiotics.