Clinical meaning
Irritable bowel syndrome (IBS) is the most common functional GI disorder, affecting 10-15% of the global population. The Rome IV criteria provide a standardized positive diagnostic framework: recurrent abdominal pain on average at least 1 day per week in the last 3 months, associated with ≥2 of: (1) related to defecation (pain improves or worsens), (2) associated with change in stool frequency, (3) associated with change in stool form (appearance). Symptom onset must be at least 6 months before diagnosis. IBS is subtyped by Bristol Stool Form Scale (BSFS): IBS-C (constipation predominant — >25% hard stools, <25% loose), IBS-D (diarrhea predominant — >25% loose, <25% hard), IBS-M (mixed — >25% hard AND >25% loose), and IBS-U (unsubtyped — insufficient abnormality in stool form). The pathophysiology involves the gut-brain axis: visceral hypersensitivity (augmented pain processing from the GI tract via visceral afferents), altered GI motility (increased transit in IBS-D, decreased in IBS-C), intestinal permeability changes, altered microbiome composition, immune activation (mast cell infiltration near nerves), and psychosocial factors (stress, anxiety, depression modulate symptoms through the brain-gut-microbiome axis). Post-infectious IBS (PI-IBS) develops...