What is irritable bowel syndrome (IBS)?

Quick Answer
A common intestinal disorder characterized by abdominal pain or discomfort and by altered bowel habits, consisting of diarrhea or constipation or alternating between diarrhea and constipation.
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Causes and Symptoms

Irritable bowel syndrome (IBS) is a gastrointestinal (GI) disorder characterized by abdominal pain or discomfort associated with diarrhea, constipation, or alternations between these two types of bowel motions. Other GI symptoms are related to this syndrome, including bloating, cramping, gas, heartburn, nausea, passage of mucus, an increased urge to defecate, and a feeling of incomplete defecation. Moreover, non-GI symptoms may accompany IBS, such as discomforts during menstruation, urination, and sexual activities. Although symptoms vary in intensity, they do not grow steadily worse over time but may wax and wane over the years.

IBS is sometimes referred to as a functional disorder. Several causes of IBS have been suggested, but there is no single organic cause that can explain this condition. IBS is understood as a disease with a common set of symptoms that are evaluated based either on the Manning criteria (established in 1978) or the Rome III criteria (updated in 2006) for standardized diagnosis of IBS and for distinguishing organic causes for the syndrome. The Manning criteria include the following: pain relief with defecation, sensation of incomplete defecation, passage of mucus, and frequent and looser stools associated with the onset of pain. The more symptoms are present, the higher the probability of IBS diagnosis. The Rome III criteria include recurrent abdominal pain or discomfort associated with two or more of the following: relief after defecation, change in frequency of stools in association with pain, and change in form or appearance of stools associated with pain. The duration of these symptoms should at least be three days per month for the past three months or the onset of symptoms should at least be six months prior to diagnosis.

Three traditional physiological factors contribute to the symptoms of IBS: changes in GI motility, psychological aspects such as stress, and GI hypersensitivity. The GI motility responds to various stimuli such as food, stress, and gut distension; the resulting changes in activity of the major part of the large intestine or colon can lead to IBS symptoms. Following food digestion by the stomach and the small intestine, the undigested material is propelled toward the rectum by peristalsis. When peristalsis becomes disrupted by IBS, the flow becomes too slow, causing constipation, or too fast, causing diarrhea.

Some foods and drinks appear more likely to trigger IBS attacks by disrupting peristalsis. Fatty foods, fried foods, milk products, chocolate, drinks with caffeine, and alcohol can exacerbate the symptoms of IBS, as well as some fruits or vegetables, such as cabbage, broccoli, cauliflower, and brussels sprouts. In some cases, however, no specific foods cause specific symptoms, as any food intake seems to worsen symptoms. Often, IBS-aggravating foods vary from person to person.

The nervous system processing between the brain and the intestines suggest that stress may be the culprit in IBS. Many IBS sufferers report symptoms following a meal when they experience stress. Psychologic stress has been shown to exacerbate GI symptoms in IBS. Stress may also be involved in some people who develop IBS following infection or inflammation of the bowel. In addition, psychiatric diseases are common among IBS patients, especially in those who are hospitalized.

A hypersensitive gut is characterized by enhanced perception of normal motility throughout the digestive tract. Recent studies have shown that specific parts of the brain show greater activation in IBS patients; these activated brain regions are associated with attention and response selection.

IBS is more commonly seen in women than in men, with up to 20 percent of the American population affected. Although it can occur at any time, IBS generally appears in the patient’s teens and twenties, and it frequently is found in members of the same family. Americans and Europeans have similar frequencies of IBS.

Treatment and Therapy

Diagnosis of IBS is an involved process that is accomplished through a series of steps. A thorough history should be provided to the physician. Symptom-based criteria (Manning or Rome III) will be used to identify IBS. Moreover, alarming symptoms such as weight loss, unrelenting diarrhea, family history of colon cancer, and psychiatric aspects such as depression and suicidal thoughts will be ruled out. A physical examination will be performed on the first visit. Laboratory tests and a colonoscopy or sigmoidoscopy may be performed, and a stool sample may be obtained—all of which will rule out serious diseases such as colon cancer, infection, and inflammatory diseases. Traditionally, IBS has been a diagnosis of exclusion.

Treatment options will include dietary and lifestyle changes, medications targeted toward the predominant symptoms, and psychological modalities. Generally, a low-fat, high-fiber diet lessens symptoms, although the tolerance of fiber as well as of all foods varies from person to person. Dietary changes vary according to the severity of the patient’s symptoms. In mild cases of IBS, known aggravating foods should be identified and avoided. Symptoms may be eased by eating smaller meals. Since no diet has been found that controls all symptoms, a diary of symptoms and food intake is valuable in determining which foods are offensive. Establishment of fixed times for meals and bathroom visits helps regulate bowel habits as well.

In addition to dietary changes, medications are given to alleviate predominant IBS symptoms. Abdominal pain is treated with antispasmodic drugs such as dicyclomine, especially if the pain is associated with meals; these drugs relax the smooth muscles of the intestines. An antidiarrheal agent such as loperamide is used to reduce loose stools and to relieve abdominal pain. A medication called alosetron (Lotronex) is also used for diarrhea. Because alosetron has serious side effects, such as severe constipation and ischemic colitis, it was withdrawn from the market for a while; it is now available again, but with specific restrictions and only for severe IBS. Physicians must enroll in a special program with the manufacturer in order to prescribe alosetron. For constipation, bulk laxatives that supply increased dietary fiber such as psyllium (Metamucil, Fiberall, Konsyl, Colon Cleanse, and other similar products) are recommended. A medication for constipation called tegaserod (Zelnorm) was made available in 2002 but was withdrawn in 2007 when evidence suggested that it raised the risk of heart attack and stroke. Lubiprostone (Amitiza), which helps promote chloride channel secretions in the bowel and thus aids perstalsis, has been approved for use in women with constipation-predominant IBS and patients with chronic constipation. Linaclotide (Linzess), a guanylate cyclase-C agonist, increases the motility and blocks pain signals in the bowels. It is approved for adults seventeen and older who have IBS with constipation or chronic constipation.

Psychological treatments are imperative for IBS patients whose quality of life is severely impaired. Patients who have concomitant psychiatric conditions such as depression, history of sexual abuse, or any major life stress should be treated for their psychiatric ailments so that they can cope better with IBS.

Psychological counseling, cognitive behavioral therapy, hypnosis, biofeedback, and relaxation techniques are recommended to reduce anxiety and encourage learning to cope better with the pain of IBS. Severe pain from IBS can be treated with antidepressants such as tricyclics. Moderate exercise has also been shown to be beneficial.

In addition to dietary changes prescribed by doctors, alternative practitioners may advise herbal remedies to treat symptoms of IBS, such as Chinese herbal medicines, aloe vera, ginger, evening primrose, fennel, peppermint extract, chamomile, and rosemary. Aromatherapy, hydrotherapy, acupuncture, chiropractic, and osteopathy as alternative treatments may also be useful in some individuals.

Perspective and Prospects

IBS was once believed to be a psychological disorder, but recent studies have shown that it is a true medical disorder with specific physiological characteristics and a significant impact on individuals who are afflicted with it. In addition, IBS has considerable effects on the society’s health care burden. It has been reported that IBS is the second most common reason for seeing a physician (the first being the common cold) and accounts for 12 percent of visits to primary care and for the largest group seen by gastroenterologists. In terms of GI diseases, IBS is second only to gastroesophageal reflux disease (GERD) as most prevalent GI disorder in the United States. IBS affects 15.4 million people, and the economic costs (both direct and indirect) are in the billions of dollars. These costs are derived from work absenteeism, doctor visits, medical tests, and procedures, as well as other related expenses.

Although there is no cure for IBS, it is not a life-threatening condition. It has not been shown to cause intestinal bleeding or inflammation, as in Crohn’s disease, ulcerative colitis, or cancer. Long-term management, though frustrating, involves commitment to therapy for six months or more to find the best combinations of medicine, diet, counseling, and support for control of IBS symptoms.


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