What is Irritable Bowel Syndrome (IBS)?
IBS is a chronic disorder of gut-brain interaction characterized by recurrent abdominal pain associated with altered bowel habits (diarrhea, constipation, or both) in the absence of structural or biochemical disease 1.
Core Clinical Features
The diagnosis requires at least 12 weeks of abdominal discomfort or pain in the preceding 12 months with at least 2 of the following 3 features 2:
- Pain relieved with defecation
- Onset associated with a change in stool frequency
- Onset associated with a change in stool form (appearance)
Supporting symptoms include abnormal stool frequency (>3/day or <3/week), abnormal stool form (lumpy/hard or loose/watery), abnormal passage (straining, urgency, incomplete evacuation), mucus passage, and bloating 2.
Prevalence and Impact
IBS affects 5-10% of the population at any given time, with a relapsing and remitting course in most patients 3, 4. It disproportionately affects young adult women and those with psychological comorbidities 3. The condition profoundly impairs quality of life, physical function, and work productivity to a degree exceeding most other medical disorders 2.
Underlying Pathophysiology
IBS represents dysregulation of the gut-brain axis 1. The pathophysiology involves three interrelated mechanisms 2:
- Altered gut reactivity - abnormal motility and secretion in response to meals, gut distention, inflammation, or psychosocial stress, producing diarrhea and/or constipation
- Visceral hypersensitivity - enhanced perception of normal gut sensations and heightened pain responses
- Brain-gut axis dysregulation - altered processing of visceral signals, increased stress reactivity, and impaired modulation of gut function
Additional contributing factors include gut microbiota alterations (dysbiosis), increased intestinal permeability, low-grade mucosal inflammation, post-infectious changes, and genetic predisposition 3, 4.
Prognosis and Management Philosophy
Cure is unlikely, but substantial improvement in symptoms, social functioning, and quality of life is achievable 1. The best-described risk factor is acute enteric infection 3. Treatment focuses on the predominant symptom pattern (constipation-predominant, diarrhea-predominant, or mixed), using dietary modifications, pharmacological therapies targeting specific symptoms, and psychological interventions when needed 1.
Key Diagnostic Principle
IBS is a positive diagnosis based on symptom criteria, not a diagnosis of exclusion 5. Limited testing to exclude celiac disease (serology), inflammatory bowel disease (fecal calprotectin), and assessment for alarm features (weight loss, rectal bleeding, anemia, fever) is appropriate 1, 5. Exhaustive investigation has low yield and should be avoided in patients meeting typical symptom criteria without alarm features 6.