Irritable Bowel Syndrome (IBS) is the most common functional gastrointestinal (GI) disorder with worldwide prevalence rates ranging from 9-23 percent and U.S. rates generally in the area of 10-15 percent. Functional disorders are conditions where there is an absence of structural or biochemical abnormalities on diagnostic tests, which could explain symptoms.
IBS is best understood as a long-term or recurrent (chronic) disorder of gastrointestinal functioning. It is characterized by multiple symptoms involving a disturbance in the regulation of bowel function that results in unusual sensitivity and muscle activity. These disturbances can produce symptoms of abdominal pain or discomfort, bloating or a sense of gaseousness, and altered bowel habits (diarrhea and/or constipation).
Abdominal pain and/or discomfort is the key symptom of IBS and is often relieved with the passing of a bowel movement (defecation). There are many causes for abdominal pain, but in IBS, the pain or discomfort is associated with a change in bowel habits. While everyone suffers from an occasional bowel disturbance, for those with IBS the symptoms are more severe, or occur more often either continuously or off and on. IBS affects men and women of all ages.
Symptoms can vary and sometimes seem contradictory, such as alternating diarrhea and constipation. The intensity and location of abdominal pain in IBS are highly variable, even at different times within a single person. The symptoms of IBS are produced by abnormal functioning of the nerves and muscles of the bowel. In IBS there is no evidence of an organic disease (where structural or biochemical abnormalities are found), yet, something—a "dysregulation" between the brain, the gut, and the central nervous system—causes the bowel to become "irritated," or overly sensitive to stimuli. Symptoms may occur even in response to normal events, such as eating a meal.
Upper gastrointestinal symptoms are commonly reported by IBS patients with 25 percent to 50 percent of patients reporting heartburn, nausea, abdominal fullness, and bloating. In addition, a significant number report intermittent upper abdominal discomfort or pain (dyspepsia).
Many IBS patients also report non-gastrointestinal symptoms such as fatigue, muscle pain, sleep disturbances, and sexual dysfunction. Up to 66 percent of IBS patients report non-gastrointestinal symptoms compared to less than 15 percent of healthy individuals. These non-gastrointestinal symptoms may be due to IBS coexistence with another disease or condition such as fibromyalgia, chronic fatigue syndrome, and interstitial cystitis. For example, the estimated prevalence of IBS in patients with fibromyalgia (FMS) is 30 percent or more with similar findings of FMS in patients with irritable bowel syndrome.