8 Chronic Pain Conditions and Their Diagnostic Criteria

5. Irritable Bowel Syndrome - Gut-Brain Axis Dysfunction

Irritable Bowel Syndrome (IBS) represents a functional gastrointestinal disorder characterized by chronic abdominal pain associated with altered bowel habits, affecting approximately 10-15% of the global population with a significant female predominance. The Rome IV criteria, established by the Rome Foundation, provide the current gold standard for IBS diagnosis, requiring recurrent abdominal pain on average at least one day per week in the last three months, with symptom onset at least six months before diagnosis. The pain must be associated with two or more of the following criteria: related to defecation, associated with a change in frequency of stool, or associated with a change in form or appearance of stool. IBS is further classified into subtypes based on predominant bowel habits: IBS with constipation (IBS-C), IBS with diarrhea (IBS-D), IBS with mixed bowel habits (IBS-M), and unclassified IBS (IBS-U). The diagnostic process emphasizes the absence of alarm features such as weight loss, rectal bleeding, family history of inflammatory bowel disease or colorectal cancer, and onset after age 50, which would warrant further investigation to exclude organic disease. Recent research has highlighted the role of the gut-brain axis in IBS pathophysiology, involving altered gut microbiota, increased intestinal permeability, immune activation, and central pain processing abnormalities. The chronic visceral pain in IBS often involves visceral hypersensitivity, where normal physiological processes become painful, and may be influenced by psychological factors, stress, and dietary triggers, making IBS a prime example of the biopsychosocial model of chronic pain.