Irritable bowel syndrome (IBS)

Summary

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder characterized by chronic abdominal pain associated with altered bowel habits. It affects approximately 10-15% of the population, with higher prevalence in women. The diagnosis is based on clinical criteria (Rome IV) and exclusion of organic disease. Management focuses on symptom control through lifestyle modifications and targeted pharmacotherapy.

Overview

• 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

Pathophysiology

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

Clinical Features

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

Diagnosis

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

Differential Diagnosis

• 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

Management

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)

Prognosis

• 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

Key Points for Exams

• 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