IBS Rome IV diagnostic criteria: recurrent abdominal pain, on average ≥1 day/week in last 3 months, associated with ≥2 of - 1) related to defecation, 2) associated with change in stool frequency, 3) associated with change in stool form/appearance. Symptoms ≥6 months. IBS-D >25% loose, <25% hard; IBS-C >25% hard, <25% loose; IBS-M both >25%; IBS-U neither. Pathophysiology - visceral hypersensitivity, altered motility, gut-brain axis dysfunction, gut microbiota imbalance, post-infectious (Salmonella, Campylobacter), genetic predisposition, low-grade mucosal inflammation, increased intestinal permeability. Female predominance (2:1).
Differential diagnosis and workup: 1) Alarm symptoms (rule out organic) - age >50 with new onset, weight loss, GI bleeding, anemia, family history of CRC/IBD/celiac, nocturnal symptoms; 2) Initial workup - CBC, CRP, fecal calprotectin (IBD screen), tTG-IgA + total IgA (celiac screen), TSH; 3) Targeted - colonoscopy if alarm features or age >45-50; SeHCAT or 7α-hydroxy-4-cholesten-3-one (bile acid diarrhea); breath tests for SIBO/lactose/fructose; abdominal imaging if indicated; 4) Differential - celiac, IBD, microscopic colitis, lactose intolerance, bile acid malabsorption, SIBO, hyperthyroidism, ovarian cancer, endometriosis, chronic pancreatitis, giardiasis.
Stepwise management: 1) Lifestyle and dietary - regular meals, avoid trigger foods, low-FODMAP diet (3 phases: elimination 4-6 weeks, reintroduction, personalization), gluten reduction (NCGS overlap), soluble fiber (psyllium for IBS-C), exercise, stress management; 2) IBS-D pharmacotherapy - loperamide (mild), antispasmodics (hyoscine, mebeverine, peppermint oil), eluxadoline 75-100 mg bid (mu-opioid agonist + delta antagonist), alosetron (5HT3 antagonist; women only, REMS), rifaximin 550 mg tid x 14 days (TARGET trials; can repeat), bile acid sequestrant (cholestyramine) if BAM; 3) IBS-C pharmacotherapy - osmotic laxative (PEG), linaclotide 290 mcg/day (guanylate cyclase-C agonist), plecanatide 3 mg/day, lubiprostone 8 mcg bid (chloride channel activator), tenapanor 50 mg bid (NHE3 inhibitor), prucalopride; 4) Gut-brain - TCA (amitriptyline 10-50 mg HS for pain/IBS-D), SSRI (citalopram, paroxetine for IBS-C with anxiety); 5) Psychological - CBT, gut-directed hypnotherapy, mindfulness.