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Irritable Bowel Syndrome and Functional Gastrointestinal Disorders
Irritable bowel syndrome (IBS) is one of a group of functional gastrointestinal (GI) disorders characterized by abdominal discomfort or pain and frequently associated with a change in bowel movements ( Fig. 61.1 ). Worldwide, IBS is the most frequent symptom complex in patients seeking GI consultation. In the United States, it is estimated that more than 3 million office and hospital visits are attributed to this symptom complex.
Irritable Bowel Syndrome.
5-HT, 5-Hydroxytryptamine; IBS, irritable bowel syndrome.
In disease classification, IBS is thought to be the intestinal or bowel disorder of a group of functional GI disorders that include (1) esophageal disorders such as globus hystericus and functional chest pain; (2) GI disorders such as functional dyspepsia (see Chapter 31 ), aerophagia, functional vomiting (see Chapter 23 ), and functional abdominal pain; (3) functional biliary disorders such as sphincter of Oddi dysfunction (see Chapter 139 ); and (4) anorectal disorders such as anorectal pain and pelvic floor dyssynergia (see Section V ).
As understanding of GI physiology broadens, the cause of IBS is thought to be a disturbance in the autonomic and enteric nervous systems of the gut and the gut-brain axis. This disturbance results in abnormal motility and visceral hypersensitivity. Early inflammation of the gut may be a trigger for the onset of the syndrome. The discovery of lactose intolerance has removed many patients from the category of IBS, and, as science evolves, it is certain that other causes may explain the symptoms in select groups of patients. The wide range of food sensitivities and food allergies that exist, as well as slow development of knowledge in this area, may progress and prove helpful in the future.
Clinical Picture
Three classic symptoms are associated with IBS: abdominal pain, diarrhea, and constipation. Alternating diarrhea and constipation, or diarrhea only, or constipation only, may prevail. In the classic model of the female patient, a woman seeks treatment for recurrent low abdominal pain associated with an inability to have a bowel movement. Constipation is persistent and becomes a lifelong problem. The patient frequently will present with many evaluations that have revealed no significant abnormality. Often, the abdominal pain is relieved by a bowel movement. Patients may or may not notice whether the character of the stool has changed, and often they describe pebblelike stools. However, the pain is persistent and may be nagging or severe, and patients may require pain relief. Characteristic is the history of frequent visits to physician offices, with a work-up that has revealed no disease.
The other common symptom complex is severe diarrhea, noted more often in male patients and consisting of loose or explosive bowel movements that may almost herald incontinence. The diarrhea is associated with severe abdominal cramps, and frequently, patients describe a formed stool on first motion, then liquid stools. Once the diarrhea has stopped, the cramps frequently cease. However, the cramps can be severe and have caused sweating during the bowel movement.
The third pattern is constant, recurrent lower abdominal pain associated with diarrheal bowel movements and, once they have subsided, days of no bowel movements or constipation with a feeling of an inability to evacuate. It is estimated that many patients never report these symptoms to physicians, but, as stated, IBS is one of the major symptom complexes treated by physicians and GI consultants.
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