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Irritable Bowel Syndrome

Last updated on May 12, 2023

Irritable Bowel SyndromeThe irritable bowel syndrome is the most common of all digestive disorders, affecting nearly everyone at one time or another and accounting for up to 50% of patients referred to a gastroenterologic practice. Although characterized as a disorder of bowel motility, in many patients it is an exaggeration of normal physiologic responses.

Numerous terms have been used to describe the syndrome (Table SYNONYMS FOR IRRITABLE BOWEL SYNDROME). Irritable bowel syndrome seems to be the most appropriate. Terms that include the word colon or colitis are inaccurate because the condition is not limited to the colon, and inflammation is not a feature. Furthermore, use of the term colitis leads to confusion with ulcerative colitis and conveys an inaccurate impression to the patient. The terms spastic bowel syndrome and nervous bowel, although inaccurate in that they do not encompass all instances of irritable bowel syndrome, may be useful in explaining the condition to some patients.


The causes and pathogenesis of irritable bowel syndrome remain obscure. Nevertheless, clinical and laboratory evidence indicate that it most likely is a disorder of bowel motility. Constipation and abdominal cramps are prominent complaints of many patients with irritable bowel syndrome. These symptoms could be explained on the basis of hypertonic segmental contractions, which would slow transit by increasing the resistance to passage of feces. On the other hand, it is possible that patients with diarrhea have a hypomotile bowel, which would decrease resistance to passage of feces, or that they simply have an increase in peristaltic contractions.

Myoelectric activity of the colon is composed of slow waves and spike potentials superimposed on the slow waves. In healthy people, slow-wave frequency ranges from 6 to 10 cycles per minute, although rates of 3 cycles per minute occur some of the time. The superimposed spike potentials take the form of short spike bursts and long spike bursts. The short spike bursts are less than 5 seconds and occur at the same time as the slow waves, resulting in muscular contractions of the same frequency as the slow waves. On the other hand, long spike bursts last from 15 seconds to several minutes and produce sustained contractions. Abnormalities in colonic myoelectric activity have been described in patients with irritable bowel syndrome but have been inconsistent and, thus far, of no practical clinical use.

Intestinal motor activity

In patients with irritable bowel syndrome the increase in colonic motor activity that normally occurs after eating is blunted but continues longer than in asymptomatic people and may even become stronger. Emotional stress also induces colonic motor activity, both in healthy people and in patients with irritable bowel syndrome, but it is possible that symptoms are perceived to a greater degree in patients with irritable bowel syndrome. Balloon distention of the rectosigmoid colon in patients with irritable bowel syndrome causes spastic contractions of greater amplitude than in asymptomatic subjects. Furthermore, there is evidence that patients with irritable bowel syndrome who complain of gaseous distention and abdominal cramps cannot tolerate quantities of small-bowel intraluminal gas that are easily tolerated by healthy people.

Diagnosis of Irritable Bowel Syndrome


Emotional support

Making the diagnosis of irritable bowel syndrome is sufficient in some patients to alleviate anxiety about their symptoms. In particular, patients who suffer from cancer phobia are relieved to learn that they are cancer-free. However, most patients with irritable bowel syndrome experience no relief merely from reassurance. Many have carried the diagnosis of irritable bowel syndrome for years and continue to experience distressful symptoms despite supportive reassurance and diet and drug therapy.

Although these patients often understand that they have a «nervous bowel» that understanding does little to alleviate symptoms, and they continue to seek treatment. Stress reduction programs may be effective. A study by Guthrie and associates showed that psychological treatment is feasible and effective in two thirds of patients with irritable bowel syndrome who do not respond to standard medical treatment.

All patients
Reassurance and emotional support
Stress reduction
Judicious use of tricyclic antidepressants and serotonin reuptake inhibitors
Patients with abdominal pain and constipation
Increase dietary fiber
Stool softeners (e.g., Colace)
Laxatives (e.g., lactulose, MiraLax, and Senokot)
Anticholinergics-antispasmodics(e.g., dicyclomine hydrochloride[Bentyl], 10-20 mg, b.i.d.-q.i.d.)
Patients with diarrhea
Antidiarrheal agents (e.g., diphenoxylate hydrochloride[Lomotil], 2.5-5.0 mg, or loperamide
hydrochloride [Imodium], 2 mg q6hprn)
Increase dietary fiber
Tricyclic antidepressants

Irritable Bowel SyndromeDiet and fiber therapy

The commonsense approach to diet therapy is the most appropriate. There is no need for bland or highly restrictive diets in the treatment of irritable bowel syndrome. Patients should avoid foods that they find cause symptoms. If lactose-containing foods produce cramps and diarrhea, these should be eliminated from the diet.

The role of fiber in the treatment of irritable bowel syndrome has been controversial. However, clinical experience suggests that a high-fiber diet and/or fiber supplements provide symptomatic relief in some patients. Patients with crampy abdominal pain and constipation seem most likely to benefit, although sometimes patients with watery diarrhea experience a firming of their stools after the fiber content of the diet has been increased.

Drug therapy


Unfortunately, drug therapy of irritable bowel syndrome often is empiric. Patients with constipation and abdominal pain may benefit from a so-called antispasmodic. These drugs are anticholinergic in their mode of action, but whether they actually relieve spasm is conjectural. A reasonable choice is dicyclomine hydrochloride, 10 to 20 mg three to four times daily, because it is less likely than others to cause unpleasant nongastrointestinal anticholinergic side effects. Regardless of what preparation is used, patients should be cautioned about the possibility of the development of dry mouth and of visual and urinary bladder disturbances.

Laxatives should be used judiciously in the treatment of the constipation of irritable bowel syndrome. However, many patients with constipation become dependent on the long-term use of laxatives and may need to be withdrawn from these agents.

Diphenoxylate hydrochloride (Lomotil) and loperamide hydrochloride (Imodium)

The diarrhea of irritable bowel syndrome often responds to low doses of diphenoxylate or loperamide hydrochloride. These drugs are synthetic opioids with low potential for abuse. They control diarrhea by reducing gastrointestinal motility and by inhibiting watery secretions. Loperamide hydrochloride (Imodium) may be preferred for long-term use because of its longer duration of action. Also, it crosses the blood-brain barrier poorly and thus is less likely to cause addiction.

Tranquilizers and antidepressants may be useful in selected patients for the short-term management of situational anxiety and depression. Low-dose tricyclic antidepressants such as amitriptyline hydrochloride (Elavil) or Norpramin (desipramine hydrochloride) may be helpful in some patients with diarrhea-predominant irritable bowel syndrome. Serotonic uptake inhibitors (SSRIs) such as fluoxetine hydrochloride (Prozac), sertraline hydrochloride (Zoloft), and paroxetine (Paxil) may help some patients with irritable bowel syndrome.

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