Irritable bowel syndrome (IBS, or spastic colon) is a symptom-based diagnosis characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits. As a functional gastrointestinal disorder (FGID), IBS has no known organic cause. Diarrhea or constipation may predominate, or they may alternate (classified as IBS-D, IBS-C or IBS-A, respectively). Historically a diagnosis of exclusion, a diagnosis of IBS can now be made on the basis of symptoms alone, in the absence of alarm features such as age of onset greater than 50 years, weight loss, gross hematochezia, systemic signs of infection or colitis, or family history of inflammatory bowel disease. Onset of IBS is more likely to occur after an infection (post-infectious, IBS-PI), or a stressful life event, but varies little with age.
Although there is no cure for IBS, there are treatments that attempt to relieve symptoms, including dietary adjustments, medication and psychological interventions. Patient education and a good doctor-patient relationship are also important.
Several conditions may present themselves as IBS, including coeliac disease, fructose malabsorption, mild infections, parasitic infections like giardiasis, several inflammatory bowel diseases, bile acid malabsorption, functional chronic constipation, small intestinal bacterial overgrowth, and chronic functional abdominal pain. In IBS, routine clinical tests yield no abnormalities, although the bowels may be more sensitive to certain stimuli, such as balloon insufflation testing. The exact cause of IBS is unknown. The most common theory is that IBS is a disorder of the interaction between the brain and the gastrointestinal tract, although another common theory is that for at least some individuals with IBS there are abnormalities in the gut flora which results in inflammation and altered bowel function.
IBS has no direct effect on life expectancy. It is, however, a source of chronic pain, fatigue, and other symptoms and contributes to work absenteeism. The high prevalence of IBS and significant effects on quality of life make IBS a disease with a high social cost. It has also been suggested that a proportion of IBS patients may develop depression and are thus more likely to commit suicide. Proposed factors for increased suicide rate in IBS patients include perceived hopelessness and poor quality of services.