[Irritable bowel syndrome. Survey of definitions, differential diagnosis and pathogenesis].

Abdominal pain/discomfort, bloating, need to rush to the toilet, straining, feeling of incomplete bowel emptying and alternating periods of diarrhea and constipation is the clinical definition of the irritable bowel syndrome. The internationally used syndrome definition is based on expert opinions and answers to patient questionnaires. When symptoms are registered prospectively, abdominal pain starts or worsens after meals and is not relieved by defecation. As in the general population patients with the syndrome define diarrhea as loose stools and constipation as hard stools regardless of stool frequencies. Variation in defecatory symptoms and discrepancies between these symptoms and stool consistency are the hallmarks of the syndrome, and the degree of variation per fortnight is relatively stable in the individual patient. Fermentation of carbohydrates by colonic bacteria, increased sensitivity to bowel distention by gas, gas-producing food, increased secretion of cholecystokinin after fatty meals and/or increased sympathetic nerve tone at stress can give rise to symptoms. Symptoms can start after a single period of bacterial gastroenteritis. Although patients seeking medical care for the syndrome are more often anxious, the syndrome itself is not psychosomatic. Symptoms are possibly mediated through partial degranulation of mast cells in bowel mucosa, but this does not make it an allergic disease. If bowel dysmotility can be measured, early stage or a mild case of intestinal pseudoobstruction should be considered. Hyperreactivity in the enteric nervous system and/or in the brain is the likely main cause of the symptoms. More widespread activity in the brain after exposure to stimuli originating from bowel nerves or less inhibition of this stimulation in the brain are possible mechanisms.