Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder: it causes recurrent abdominal pain with a change in bowel habit, yet routine tests show no structural or biochemical disease to explain the symptoms.
Two ideas organise the topic. The first is that IBS is a disorder of the gut–brain interaction: the gut is not damaged, but its motility, its sensation and the way it handles gas and fluid are disturbed, and psychological and immune signals feed into the same loop. The second is that there is no single diagnostic test, so IBS is recognised from the pattern of symptoms — the current reference definition is Rome IV — and testing is used mainly to rule out conditions that look similar.
Choose a route through this topic
- Epidemiology and Natural History of IBS — how common IBS is, who it affects, why the reported figures vary, and how it behaves over time.
- Risk Factors and Pathophysiology of IBS — the risk factors, led by prior infectious gastroenteritis, and the mechanisms proposed to explain the symptoms.
- Clinical Features and Diagnostic Criteria of IBS — how IBS presents, the Manning, Kruis and Rome IV criteria, and the IBS subtypes.
- Diagnosis and Treatment of IBS — physical examination, the exclusion work-up guided by alarm features, and how the condition is managed.
If the topic is new, start with the epidemiology for the population picture and the pathophysiology for the mechanisms; the last two notes are the clinical core, from recognition through to treatment.