In gastroenterology, irritable bowel syndrome (IBS) is a functional bowel disorder characterized by mild to severe abdominal pain, discomfort, bloating and alteration of bowel habits. In some cases, the symptoms are relieved by bowel movements. Diarrhea or constipation may predominate, or they may alternate (classified as IBS-D, IBS-C or IBS-A, respectively). IBS may begin after an infection (post-infectious, IBS-PI) or a stressful life event. Other functional or pain disorders and certain psychological conditions are more common in those with IBS.

Although there is no cure for IBS, there are treatments which 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 as IBS including celiac disease, mild infections, parasitic infections like giardiasis, several inflammatory bowel diseases, functional chronic constipation and chronic functional abdominal pain. In IBS, routine clinical tests yield no abnormalities, though 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 there may also be abnormalities in the gut flora or the immune system.

Symptoms

The primary symptoms of IBS are abdominal pain or discomfort in association with frequent diarrhea and/or constipation, a change in bowel habits. There may also be urgency for bowel movements, a feeling of incomplete evacuation (tenesmus), bloating or abdominal distention. People with IBS more commonly than others have gastroesophageal reflux, symptoms relating to the genitourinary system, psychological symptoms, fibromyalgia, headache and backache.

IBS can be classified as either diarrhea-predominant (IBS-D), constipation-predominant (IBS-C) or IBS with alternating stool pattern (IBS-A or pain-predominant ). In some individuals, IBS may have an acute onset and develop after an infectious illness characterised by two or more of the following: fever, vomiting, diarrhea, or positive stool culture. This post-infective syndrome has consequently been termed "post-infectious IBS" (IBS-PI).

Diagnosis

There is no specific laboratory or imaging test which can be performed to diagnose irritable bowel syndrome. Diagnosis of IBS involves excluding conditions which produce IBS-like symptoms, and then following a procedure to categorize the patient's symptoms.