A unifying hypothesis for the functional gastrointestinal disorders: really multiple diseases or one irritable gut?

The functional gastrointestinal disorders are defined by the Rome criteria as a heterogeneous group of symptom-based conditions that have no structural or biochemical explanation. However, this definition now seems outdated, because structural and molecular abnormalities have begun to be recognized in subsets of patients with the irritable bowel syndrome (IBS), the prototypic functional bowel disease. A complex classification system based arbitrarily on symptom criteria does not fit in with a number of emerging facts. For example, the symptom overlap of IBS with gastroesophageal reflux disease is not due to chance, and the emergence of post-infectious IBS, dyspepsia, or both after Salmonella gastroenteritis fits better with a 1-disease model. A new paradigm seems to be needed. All of these disorders may arise after infection or gut inflammation, but the phenotype depends on localized neuromuscular dysfunction in the predisposed human host (the "irritable gut").