Irritable bowel syndrome (IBS) is a disorder of the entire digestive tract that causes recurring abdominal pain and constipation or diarrhea.
IBS affects about 10 to 15% of the general population. Some but not all studies suggest women with IBS are more likely to consult a doctor. IBS is the most common disorder diagnosed by gastroenterologists (doctors who specialize in disorders of the digestive tract).
IBS is generally classified as a functional disorder because it impairs the functioning of the body's normal activities, such as the movement of the intestines, the sensitivity of the nerves of the intestines, or the way in which the brain controls some of these functions. However, although the normal functioning is impaired, there are no structural abnormalities that can be found with an endoscope (a flexible viewing tube), x-rays, biopsies, or blood tests. Thus, IBS is identified by the characteristics of the symptoms and, when done, normal results of tests.
The cause of IBS is not clear. In many people with IBS, the digestive tract is especially sensitive to many stimuli. People may experience discomfort caused by intestinal gas or contractions that other people do not find distressing. Although the changes in bowel movements that occur with IBS might seem to be related to abnormal intestinal contractions, not all people with IBS have abnormal contractions, and in many of those who do, the abnormal contractions do not always coincide with symptoms. In some people, symptoms of IBS begin after an episode of gastroenteritis (see Gastroenteritis).
Emotional factors (for example, stress, anxiety, depression, and fear), diet, drugs (including laxatives), hormones, or minor irritants may trigger or worsen a flare-up (a bout or attack) of IBS. For some people, high-calorie meals or a high-fat diet may be a trigger (precipitating factor). For other people, wheat, dairy products, beans, chocolate, coffee, tea, some artificial sweeteners, certain vegetables (such as asparagus or broccoli), or stone fruits (such as apricots) seem to aggravate the symptoms. These foods contain carbohydrates that are poorly absorbed by the small intestine. The carbohydrates become fermented by bacteria in the intestine, which causes gas, bloating, and cramping. Because many food products contain several ingredients, it may be difficult to identify the specific trigger. Other people find that eating too quickly or eating after too long a period without food stimulates a flare-up. However, the relationship is inconsistent. People do not always get symptoms after a usual trigger, and symptoms often appear without any obvious trigger. It is not clear how all the triggers relate to the cause of IBS.
IBS tends to begin in the teens and 20s, causing bouts of symptoms that recur at irregular periods. The start of IBS symptoms in late adult life is less common but not rare. Flare-ups almost always occur when a person is awake, and they rarely wake a person from sleep.
Symptoms include abdominal pain related to or relieved by having a bowel movement (defecation), change in stool frequency (such as constipation or diarrhea) or consistency (loose or lumpy and hard), abdominal expansion (distention), mucus in the stool, and the sensation of incomplete emptying after defecation. The pain may come in bouts of continuous dull aching or cramps, usually over the lower abdomen. Bloating, gas, nausea, headaches, fatigue, depression, anxiety, muscle aches, and difficulty concentrating are other possible symptoms. In general, the character and location of pain, triggers, and the pattern of bowel movements are relatively consistent over time. However, symptoms may increase or decrease in severity and also change over time.
Most people with IBS appear healthy. Doctors base the diagnosis on the characteristics of the person's symptoms. Doctors also use standardized symptom-based criteria for diagnosing IBS called the Rome criteria. They may also do tests to diagnose common illnesses that can cause similar symptoms, particularly when people are over 40 or have warning signs such as fever, weight loss, rectal bleeding, vomiting.
Doctors diagnose IBS in people who have had abdominal pain or discomfort for at least 3 days per month in the last 3 months along with 2 or more of the following:
A physical examination generally does not reveal anything unusual except sometimes tenderness over the large intestine. Doctors do a digital rectal examination, in which a gloved finger is inserted in the person's rectum. Women undergo a pelvic examination. Doctors usually do some tests—for example, blood tests, a stool examination, and a sigmoidoscopy (see Endoscopy)—to differentiate IBS from Crohn disease, ulcerative colitis, cancer (mainly in people over age 40), collagenous colitis, lymphocytic colitis, celiac disease, and the many other diseases and infections that can cause abdominal pain and changes in bowel habits. These test results are usually normal in people with IBS, although the stool may be watery, and the sigmoidoscopy procedure may cause an unusual amount of spasms and pain. Doctors usually do more tests, such as ultrasonography of the abdomen, x-rays of the intestines, or a colonoscopy (see Endoscopy), in older people and in people who have symptoms that are unusual for IBS, such as fever, bloody stools, weight loss, and vomiting. Doctors may do a test to rule out lactose intolerance or bacterial overgrowth and also ask questions to rule out laxative abuse.
Other digestive tract disorders (such as appendicitis, gallbladder disease, ulcers, and cancer) may develop in a person with IBS, particularly after age 40. Thus, if a person's symptoms change significantly, if new symptoms develop, or if symptoms are unusual for IBS, further testing may be needed.
Because IBS symptoms can be triggered by stress and emotional conflicts, doctors ask questions to help identify stress, anxiety, or mood disorders.
Treatment differs from person to person. If particular foods or types of stress appear to bring on the problem, they should be avoided if possible. For most people, especially those who tend to be constipated, regular physical activity helps keep the digestive tract functioning normally.
Many people do better eating frequent, smaller meals rather than less frequent, larger meals (for example, five or six small meals rather than three large meals a day). People should try to slow their pace while eating. People with bloating and increased gas (flatulence) should avoid beans, cabbage, and other foods that are difficult to digest. Sorbitol, an artificial sweetener used in dietetic foods and in some drugs and chewing gums, should not be consumed in large amounts. Fructose, a sugar found in fruits, berries, and some plants, should be eaten only in small amounts. A low-fat diet helps some people, particularly those whose stomach empties too slowly or too quickly. People who have both IBS and lactase deficiency should consume dairy products in moderation.
Constipation can often be relieved by eating more fiber. People with constipation can take a tablespoon of raw bran with plenty of water and other fluids at each meal, or they can take psyllium mucilloid supplements with two glasses of water. Increasing the dietary fiber may aggravate flatulence and bloating. Occasionally, such flatulence may be reduced by switching to a synthetic fiber preparation (such as methylcellulose).
Certain laxatives are reasonably safe and often effective for people with constipation. Such laxatives include those containing sorbitol, lactulose, or polyethylene glycol, and stimulant laxatives such as those containing bisacodyl or glycerin. The laxative lubiprostone and a newer drug called linaclotide may also relieve constipation. Rarely, doctors may use tegaserod to relieve constipation that does not respond to other drugs.
Anticholinergic drugs, such as hyoscyamine, can relieve abdominal pain by blocking spasms of the intestinal muscles but often cause anticholinergic side effects (see see Sidebar 1: Anticholinergic: What Does It Mean?), such as dry mouth, blurred vision, or difficulty urinating.
Antidiarrheal drugs, such as diphenoxylate or loperamide, help people with diarrhea. Alosetron, which decreases the effects of serotonin (a chemical messenger in the body), is rarely used because it has been associated with increasing the risk of ischemic colitis.
Probiotics, which are bacteria naturally found in the body that promote the growth of good bacteria, may alleviate IBS symptoms, particularly bloating. Aromatic oils, such as oil of peppermint, often help symptoms of cramping.
Behavior modification techniques (such as cognitive-behavioral therapy), psychotherapy, and hypnosis are often extremely effective for managing symptoms of IBS. Long-term use of certain antidepressants such as nortriptyline or desipramine is safe and often helpful. Antidepressants may not only relieve pain and other symptoms but also may help relieve sleep problems and depression or anxiety.
Last full review/revision August 2013 by Stephanie M. Moleski, MD