Irritable bowel syndrome (IBS)

• IBS is a functional disorder - no structural or biochemical abnormalities detectable by conventional tests
• Characterized by recurrent abdominal pain + altered bowel habits (diarrhea, constipation, or both)
• Peak onset: late teens to early 20s
• Female predominance (14% vs 9% in males)
• 50% of patients have comorbid psychiatric conditions (anxiety, depression)
• Does NOT increase risk of colorectal cancer or IBD

The exact mechanism is unclear, but multiple factors contribute:

• Visceral hypersensitivity: Heightened pain perception to normal gut stimuli
• Altered gut motility: Abnormal intestinal contractions
• Gut-brain axis dysfunction: Abnormal communication between CNS and enteric nervous system
• Post-infectious changes: Can develop after acute gastroenteritis
• Microbiome alterations: Changes in gut bacterial composition
• Psychosocial factors: Stress and emotional factors influence symptom expression

Core Symptoms:

• Abdominal pain/discomfort
  • Crampy, diffuse
  • Related to defecation (improves or worsens)
  • Often triggered by meals or stress
• Altered bowel habits
  • Change in stool frequency
  • Change in stool form/consistency
  • May have mucus in stools
• Additional symptoms: Bloating, abdominal distension, urgency, incomplete evacuation

Rome IV Criteria:

Recurrent abdominal pain ≥1 day/week for the past 3 months, associated with ≥2 of the following:

• Related to defecation
• Change in stool frequency
• Change in stool form (appearance)

IBS Subtypes:

• IBS-D (Diarrhea-predominant): >25% loose stools, <25% hard stools
• IBS-C (Constipation-predominant): >25% hard stools, <25% loose stools
• IBS-M (Mixed): >25% loose AND >25% hard stools

Alarm Features (Red Flags):

Presence suggests organic disease - require further investigation:

• Age of onset ≥50 years
• Unintentional weight loss
• Nocturnal or progressive symptoms
• Blood in stools
• Iron deficiency anemia
• Family history of colorectal cancer or IBD
• Elevated inflammatory markers (CRP, calprotectin)

See ( table 1) for diagnostic criteria and alarm features.

Diagnostic Approach:

• IBS-C: CBC to exclude anemia
• IBS-D: CBC, celiac serology, inflammatory markers (CRP, fecal calprotectin), stool studies
• Colonoscopy: Only if alarm features present or age >50

• Inflammatory bowel disease: Bloody diarrhea, elevated inflammatory markers, abnormal colonoscopy
• Celiac disease: Positive serologies, malabsorption symptoms
• Colorectal cancer: Age >50, bleeding, weight loss, anemia
• Medication side effects: Metformin (diarrhea), opioids (constipation)
• Functional dyspepsia: Upper GI symptoms without bowel habit changes
• Ovarian cancer: Older women, bloating, early satiety, weight loss

General Approach:

1. Lifestyle modifications (all patients):
   • Regular meals, adequate sleep
   • Exercise
   • Stress management
2. Dietary changes:
   • Avoid trigger foods (alcohol, caffeine, gas-producing foods)
   • Consider low FODMAP diet
   • Increase soluble fiber (psyllium)

Pharmacotherapy:

Treatment is symptom-targeted - see ( table 2)

For Abdominal Pain:

• First-line: Antispasmodics (hyoscyamine, dicyclomine) - as needed
• Second-line: Tricyclic antidepressants (amitriptyline, nortriptyline)
  • Low doses for analgesic effect
  • Good for IBS-D (anticholinergic effects slow transit)
  • Avoid in IBS-C

For IBS-D (Diarrhea):

• First-line:
  • Soluble fiber (psyllium)
  • Loperamide (as needed)
• Second-line:
  • Bile acid sequestrants (cholestyramine)
  • 5-HT3 antagonists (alosetron) - restricted use

For IBS-C (Constipation):

• First-line:
  • Soluble fiber (psyllium)
  • Osmotic laxatives (polyethylene glycol)
• Second-line:
  • Lubiprostone
  • Linaclotide (guanylate cyclase agonist)

• Chronic condition with fluctuating symptoms
• 80% of patients improve over time
• Does NOT increase risk of:
  • Colorectal cancer
  • Inflammatory bowel disease
  • Other organic GI diseases
• Main impact is on quality of life

• Young patient + chronic abdominal pain + altered bowel habits + relief with defecation = IBS
• Nocturnal symptoms suggest organic disease, NOT IBS
• Diagnosis is clinical - avoid unnecessary tests without red flags
• Treatment is symptom-based, not curative
• Strong association with psychiatric comorbidities
• More common in women and young adults