Irritable bowel syndrome (IBS)
Irritable bowel syndrome (IBS) is a chronic, relapsing disorder of gut-brain interaction characterised by recurrent abdominal pain and altered bowel habit. Symptoms fluctuate, can be debilitating, and often require a pragmatic, multimodal approach directed by the predominant symptom phenotype and the need to exclude organic disease (NICE CG61).
Pathophysiology
IBS is multifactorial and incompletely understood. Contributing mechanisms include altered gut-brain signalling with visceral hypersensitivity, abnormal motility, post‑infectious changes, altered microbiota and fermentation of dietary components, genetic susceptibility, psychosocial factors, and drug or alcohol effects. These factors interact, producing variable presentations that may change over time.
Clinical features and classification
The core symptom is recurrent abdominal pain associated with a change in stool form and/or frequency. Pain may be related to defaecation and is commonly accompanied by bloating, mucus in the stool (without blood), urgency, or a sensation of incomplete evacuation.
Classify by predominant stool form (Bristol Stool Form Scale) to guide management:
- IBS‑D - diarrhoea predominant (most common)
- IBS‑C - constipation predominant
- IBS‑M - mixed bowel habits (alternating)
- IBS‑U - unclassified (meets IBS criteria but not one subtype)