In medicine (gastroenterology), irritable bowel syndrome (IBS) is a group of functional bowel disorders which are fairly common and make up 20–50% of visits to a specialist.

Features

Symptoms of IBS are abdominal pain or discomfort associated with changes in bowel habits in the absence of any structural abnormality. Colonic hypersensitivity is a sensitive but less specific sign of IBS. Depending on the kind of discomfort and bowel habits, IBS is also known as spastic colon, and can be subclassified into diarrhea-predominant (IBS-D), constipation-predominant (IBS-C) and IBS with alternating stool pattern (IBS-A). Typical is the overlap of IBS with chronic pelvic pain (this is probably due to misdiagnosis by the gynaecologist), fibromyalgia and mental disorder.

Diagnosis

According to the Rome II consensus conference of the American Gastroenterological Association and international medical societies on functional bowel disorders, the diagnosis of IBS can be made when the following criteria are fulfilled: At least 12 weeks, which need not be consecutive, in the preceding 12 months of abdominal discomfort or pain that has 2 of 3 features:

1. Relieved with defecation; and/or
2. Onset associated with a change in frequency of stool; and/or
3. Onset associated with a change in form (appearance) of stool.

Symptoms that cumulatively support the diagnosis of IBS

• Abnormal stool frequency (for research purposes, “abnormal” may be defined as greater than 3 bowel movements per day and less than 3 bowel movements per week);
• Abnormal stool form (lumpy/hard or loose/watery stool);
• Abnormal stool passage (straining, urgency, or feeling of incomplete evacuation);
• Passage of mucus;
• Bloating or feeling of abdominal distention.

(Source: AGA.)

The diagnosis of a functional bowel disorder always presumes the absence of a structural or biochemical explanation for the symptoms. This has to be excluded carefully via:

• colonoscopy
• esophagogastroduodenoscopy (EGD)
• abdominal ultrasound
• blood tests: full blood count, liver enzymes, electrolytes, renal function
• stool chemistry (e.g. tests for exocrine pancreas insufficiency and other malabsorption conditions), stool microbiology, fecal fat
• H₂-tests for lactose intolerance and fructose malabsorption
• deep duodenal biopsy or blood tests for celiac disease

A diagnostic test for IBS via assessment of colonic/rectal hypersensitivity using a barostat is currently being discussed. However, sensitivity and specificity are not yet high enough to render the method widely applicable.

Pathophysiology

Research on the etiology of IBS has not yet brought forth unanimous results. Changes in colonic motility and immunologic causes have been discussed. Hypersensitivity of the gut is a major finding in IBS patients. The association of IBS with stress is less clear. About 50% of women with IBS report a history of sexual or physical abuse.

About 25% of patients develop symptoms after a hefty enteritis (partially after use of antibiotics, see also diarrhea). In these cases, a prolonged immune reaction is currently discussed as pathogenetic. So far, this is mainly based on experiments in the animal model.

IBS is widely regarded as a conglomeration of disorders with similar symptoms but a different etiology ("trash can"). As with many other medical conditions, there is a lot of speculation about causes, including in the field of alternative medicine.

Treatment

The most important therapeutic measure is reassuring the patient that he has no fatal or otherwise threatening disease, as this is the major concern of patients seeking medical help. Dependent on symptoms, treatment can consist of dietary advice, stool softeners and laxatives in constipation-predominant, and antidiarrheals (loperamide) in diarrhea-predominant IBS. The use of antispasmodic drugs is not encouraged as the therapeutic benefit over placebo is hardly proven. Newer drugs include Alosetron and Tegaserod, both of which are heavily advertised but have only a limited effect. Psychotherapy is another treatment option, however many patients refuse to undertake one. Though not specifically indicated for IBS, the use of antidepressant drugs (e.g. amitriptyline in a low dosage or an SSRI) to treat the symptoms is common and has positive effects for some patients.

Including more soluble fiber ("white carbs", such as potatoes, pasta, rice, and white bread) in the diet is a non-pharmacological approach that has been known to provide some relief for many suffering from diarrhea-predominant and abdominal pain-predominant IBS, and possibly the other forms as well.

Epidemiology

Point prevalence is 10 - 20% of the general population of Western countries with a much higher lifetime prevalence. Prevalence is similar in India, Japan and China. IBS is less common in Thailand and rural South African areas. In Western countries, but not in India or Sri Lanka, females have a greater risk to develop IBS.

However, of the persons who have symptoms of IBS, only a proportion seeks medical help. However, there is not yet a predictor known for who will seek medical help and who will not.

Prognosis

IBS is not fatal nor is linked to the development of other serious bowel diseases. However, due to the chronic pain, discomfort and other symptoms, work absenteeism, social phobias and other negative quality-of-life effects can be common in more serious cases. Individuals lucky enough to find a successful treatment for their symptoms can lead normal lives.

Reference

• Thompson WG, Longstreth GL, Drossman DA et al. (2000). Functional Bowel Disorders. In: Drossman DA, Corazziari E, Talley NJ et al. (eds.), Rome II: The Functional Gastrointestinal Disorders. Diagnosis, Pathophysiology and Treatment. A Multinational Consensus. Lawrence, KS: Allen Press.

External Links

• IBS Self Help and Support Group (http://www.ibsgroup.org/)
• IBS Self Help and Support Group UK (http://www.ibsnetwork.org.uk/)

See also

syndrome