Irritable Bowel Syndrome

– A noninflammatory motility disorder of the large bowel that alters bowel habits and causes abdominal pain and distention.

Causes and Incidence

The cause of irritable bowel syndrome (IBS) is unknown, but it is associated with diet, drugs, toxins, gastrointestinal (GI) hormones, prostaglan-dins, and emotional factors. IBS is a common GI disorder that accounts for about half of all presenting GI complaints in the United States. Women are affected more often than men, and whites and Jews more often than other ethnic groups. All age groups are affected, although the disease is predominant in those under 35 years of age.

Disease Process

The pathophysiology of IBS is still unclear. However, two patterns can be identified: one with painful constipation and diarrhea and the other with painless diarrhea. Hypermotility with high-amplitude pressure waves is present in painful IBS, and hypomotility in painless IBS. Myoelectric activity is increased in both patterns, as is contractile activity after meals.


The primary symptoms are either painless, urgent diarrhea that occurs after meals, or alternating diarrhea and constipation accompanied by abdominal pain, bloating, flatulence, headache, and fatigue.

Potential Complications

IBS is associated with an increased risk of diverticulitis and colon cancer.

Diagnostic Tests

A careful history of bowel habits and emotional stimuli, along with a rectal examination that elicits pain in a tender rectum, is important. Manometric studies are done to evaluate electrical response, as are tests to rule out other bowel diseases.



Anticholinergics to reduce pain; bulk-forming agents, antidiarrheal drugs to regulate stool.

Highfiber, lowlactose, caffeine-free, low-fat diet; counseling for emotional effects.