Summary

Irritable bowel syndrome (IBS) is a common condition that is benign and not life-threatening, but that can impact a person's quality of life. The exact cause of IBS remains unknown and there is no single diagnostic test for it. The diagnosis is made in people fulfilling criteria in whom other diagnoses have been ruled out. Treatment should be directed at symptoms. The most important component of treatment lies in the establishment of a therapeutic physician-patient relationship.

Sections:

• What is Irritable Bowel Syndrome?
• What causes IBS?
• How is IBS diagnosed?
• What is the treatment for IBS?

What is Irritable Bowel Syndrome?

Irritable bowel syndrome (IBS) is a chronic and benign condition characterized by abdominal discomfort and altered bowel function, in the absence of structural and biochemical abnormalities. People with IBS tend to come to their doctors with complaints of
abdominal pain and either diarrhea, constipation, or alternating diarrhea and constipation. Their pain tends to be crampy and located in the lower abdomen. The nature, severity, and location of pain can vary considerably from person to person. Some people notice that emotional stress and eating worsen the pain, and that having a bowel movement relieves the pain.

IBS is the most commonly diagnosed gastrointestinal condition and is present in 10-15 percent of North Americans. Only 15 percent of those with symptoms actually seek medical attention. IBS accounts for a significant number of visits to primary care physicians, and represents 25 to 50 percent of all referrals to gastroenterologists. While IBS is not life-threatening,
it has a significant impact on quality of life.  It is the second highest cause of missed work after the common cold, and estimated direct costs of IBS are $1.4 billion per year. Individuals
with IBS can be any age, but tend to be young to middle-aged at the time of diagnosis. In general, more women than men (in a ratio of 2:1) have IBS.
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What causes IBS?

We do not know the answer to this question. IBS is likely caused by a combination of several alterations in the normal gut that are difficult to measure. There has been a great deal of research in the field of IBS, but questions still remain. 

Some researchers suspect that IBS is caused by abnormal gastrointestinal motility (how the intestines contract to propel food and waste).  However, studies of colonic motility and of small bowel motility have inconsistent results. Other researchers suspect that there is an alteration in the way the body perceives pain signals from the gut — so-called "visceral hypersensitivity." For instance, studies suggest that there is not more gas present in patients who complain of bloating and excess gas, but there is impaired handling of the gas and altered perception of its presence. Other studies suggest there might be microscopic inflammation present in the lining of the bowels of individuals with IBS. Not one theory has been proven to be consistently correct, and it is likely that there are several factors that contribute to IBS.

There is a somewhat unique subset of IBS that is called "post-infectious IBS." People who have had an episode of acute bacterial gastroenteritis ("stomach flu" or food poisoning caused by a bacterium) have been found to have a 12-fold increased risk of developing new IBS symptoms in the same year. Risk factors associated with the development of persistent symptoms include a prolonged duration of diarrhea following the initial attack, female gender, and younger age. Patients who had vomiting as part of their initial illness were less likely to develop persistent bowel symptoms. The cause of persistent or new bowel symptoms following acute infection is uncertain although several theories have been proposed.
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How is IBS diagnosed?

There is no single blood test for IBS, and other intestinal disorders can have symptoms similar to those found in IBS. Examples of these disorders include malabsorption (abnormal absorption of nutrients as is found in celiac disease), inflammatory bowel disease (such as ulcerative colitis and Crohn's disease), and microscopic colitis (an uncommon disease associated with intestinal inflammation). Symptom-based criteria have been developed to help diagnose IBS.

Examples of these are the Manning Criteria and the Rome II Criteria.

Symptom-based Diagnostic Criteria Manning Criteria:

• Pain relieved with defecation
  
• More frequent stools at onset of pain
  
• Looser stools at onset of pain
  
• Visible abdominal distension
  
• Passage of mucus
  
• Sensation of incomplete evacuation

Rome II Criteria:
In the absence of structural or metabolic abnormalities to explain the symptoms,

• At least 12 weeks or more, which need not be consecutive, in the preceding 12 months of abdominal discomfort or pain that has two out of three features:
  
  1) Relieved with defecation; and/or
  
  2) Onset associated with change in frequency of stool; and /or
  
  3) Onset associated with change in form (appearance) of stool.
  
  
• Symptoms that cumulatively support the diagnosis of irritable bowel syndrome:
  
  
• Abnormal stool frequency -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

Additionally, a medical history, physical examination, and select tests can help to rule out other conditions. "Alarm symptoms" that include rectal bleeding and unintentional weight loss are not seen with IBS. Other features that are not consistent with IBS include loss of appetite, progressive symptoms, or pain that awakens patients from sleep or prevents sleep. These symptoms need to be evaluated further if they are present.

There is debate among experts as to how much testing should be done to diagnose IBS and exclude other diagnoses. Most would agree that a combination of blood tests, stool tests and possible examination of the colon (with sigmoidoscopy or colonoscopy) should take place. These tests are directed at the patient's specific symptoms. By appropriately utilizing the right tests, other diseases are ruled out in over 95 percent of patients, meaning that fewer than 5 percent of patients with another disease will be incorrectly diagnosed.
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What is the treatment for IBS?

While there is no cure for IBS, several treatments are available that can help relieve symptoms. Treatment is more likely to be successful when patients gather information and work closely with their doctors to tailor a treatment plan.

Dietary changes

Some patients with IBS are intolerant of dairy products (lactose intolerant). A trial period during which dairy products are excluded from the diet can help make this diagnosis. Additionally, patients may be advised to decrease the amount of gas-forming foods they ingest.
Exclusion of foods that increase flatulence (beans, broccoli, cauliflower, onions, celery, carrots, raisins, bananas, apricots, prunes, brussel sprouts, wheat germ, pretzels, and bagels) should be considered in patients who complain of gas. 

An increase in the intake of fiber is generally recommended, either through diet or the use of commercial bulking supplements. Fiber might help by absorbing and holding water in the stool and increasing its bulk. If fiber supplements are used, they should be increased slowly until the desired effect is reached. Fiber seems to be most helpful in IBS patients with constipation but can also help improve consistency of stools in patients with diarrhea.

Non-medical therapies

Hypnosis, biofeedback, and psychotherapy may be helpful in some patients, especially those who find that stress triggers their symptoms. Also, if there are co-existent psychological symptoms, treating these tends to improve IBS symptoms as well.

Medications

Different medications can be directed at the symptoms of IBS. Antispasmodic medicines that relieve intestinal spasms such as dicyclomine and hyoscyamine may be beneficial in patients with pain after eating, gas, bloating, and fecal urgency. Loperamide (Imodium®) is helpful in treating the diarrhea, but not the pain of IBS. Low dose antidepressants have been found to improve symptoms in some patients with IBS. Tegaserod (Zelnorm®) has been found to decrease symptoms in women with constipation-predominant IBS. There are not enough studies to know if antibiotics, probiotics or alternative therapies are effective.

For additional information visit the American Gastroenetrological Association: www.gastro.org and the National Institute of Diabetes & Digestive & Kidney Diseases: www.niddk.nih.gov
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