Irritable Bowel Syndrome (IBS)

1. What Is IBS?

Irritable Bowel Syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by recurrent abdominal pain associated with changes in stool frequency and/or form, without structural or biochemical abnormalities on routine testing.

In simple terms:

The gut looks normal (on colonoscopy, imaging) but functions abnormally.

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2. Epidemiology & Impact

• Prevalence: ~5–10% of the population worldwide, depending on criteria used.

• More common in:

  • Females (especially in Western countries)

  • Young to middle-aged adults (often < 50 years)

• Strong association with:

  • Anxiety, depression

  • Reduced quality of life

  • Increased healthcare use (frequent clinic visits, tests, etc.)

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3. Pathophysiology (Why IBS Happens)

IBS is multifactorial. No single cause, but several mechanisms interact:

1. Visceral hypersensitivity

   • The intestines are “too sensitive” → normal gas or stool distension causes pain.

2. Abnormal gut motility

   • Accelerated transit → diarrhea-predominant IBS (IBS-D)

   • Delayed transit → constipation-predominant IBS (IBS-C)

3. Brain–gut axis dysregulation

   • Stress, anxiety, and psychological factors affect gut motility and sensation via neural and hormonal pathways.

4. Post-infectious changes

   • Some patients develop IBS after gastroenteritis (post-infectious IBS).

   • Thought due to persistent low-grade inflammation, altered microbiota.

5. Altered gut microbiota & bile acid malabsorption

   • Changes in gut flora and bile acid handling can contribute to diarrhea and bloating.

Key idea for exams: IBS = functional gut disorder involving brain–gut axis + visceral hypersensitivity + motility changes, not a structural disease.

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4. IBS Subtypes (Rome IV)

Subtypes are based on stool consistency on days with abnormal stools:

• IBS-C (constipation-predominant)

  • Hard or lumpy stools ≥25% of bowel movements

  • Loose/watery stools <25%

• IBS-D (diarrhea-predominant)

  • Loose or watery stools ≥25%

  • Hard/lumpy <25%

• IBS-M (mixed type)

  • Both hard/lumpy and loose/watery stools ≥25%

• IBS-U (unclassified)

  • Do not meet criteria above but still fulfill IBS definition

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5. Diagnostic Criteria (Rome IV)

Rome IV Criteria for IBS: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 better or worse with bowel movement)

2. Associated with change in stool frequency

3. Associated with change in stool form (appearance)

Symptoms should start ≥6 months before diagnosis.

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6. Red Flags (“Alarm Features”) – Not IBS

If any of these are present, you must think of organic disease (e.g., IBD, colorectal cancer) and investigate more:

• GI bleeding (hematochezia, melena, positive FOBT)

• Unintentional weight loss

• Fever

• Nocturnal diarrhea

• Iron-deficiency anemia

• Family history of colorectal cancer, IBD, celiac disease

• Onset after age 50

• Abdominal mass, organomegaly

• Persistent, severe, or progressively worsening pain

If red flags are present → colonoscopy, imaging, labs as appropriate.

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7. Approach to Diagnosis

7.1 Basic Evaluation

IBS is a clinical diagnosis after:

1. History fitting Rome IV criteria

2. Absence of red flags

3. Limited basic investigations are normal.

Typical initial tests (depending on setting):

• CBC (anemia, infection)

• CRP or ESR (inflammation)

• Basic metabolic panel

• Celiac serology (especially IBS-D in some regions)

• Stool tests if infectious or inflammatory diarrhea suspected

Colonoscopy is usually reserved for:

• Red flags

• Older age (e.g., ≥ 45–50 years)

• Atypical symptoms

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8. Clinical Features

Common symptoms:

• Abdominal pain:

  • Crampy, often lower abdomen

  • Relieved or worsened by defecation

• Altered bowel habits:

  • Diarrhea: frequent, urgent, small-volume stools

  • Constipation: hard stools, straining, sensation of incomplete evacuation

  • Alternating D/C in IBS-M

• Bloating and gas

• Mucus in stool (common but benign in IBS)

Systemic signs such as fever, weight loss, or nocturnal symptoms are not typical of IBS.

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9. Management of IBS

Key Principles

1. Confirm diagnosis and reassure: “This is real, but not dangerous, not cancer.”

2. Identify subtype (IBS-C, IBS-D, IBS-M).

3. Lifestyle and diet first; pharmacotherapy based on predominant symptom.

4. Address psychological comorbidities.
   

9.1 Non-Pharmacologic Management

A. Patient Education & Reassurance

• Explain functional nature → reduces anxiety and health-care seeking.

• Emphasize chronic but benign course.

B. Diet

1. Low-FODMAP diet (strong evidence)

   • Temporarily reduce fermentable oligo-, di-, mono-saccharides and polyols (e.g., certain fruits, wheat, onions, garlic, milk with lactose).

   • Trial for 4–6 weeks, then reintroduce gradually.

2. Fiber

   • Soluble fiber (psyllium) is helpful, especially in IBS-C.

   • Insoluble fiber (bran) may worsen bloating and pain.

3. Avoid or reduce:

   • Caffeine

   • Alcohol

   • Fatty foods

   • Carbonated drinks

   • Large heavy meals

C. Lifestyle

• Regular aerobic exercise (30–45 min, most days)

• Adequate sleep

• Stress management (breathing, yoga, mindfulness)

D. Psychological Therapies

• Cognitive behavioral therapy (CBT)

• Gut-directed hypnotherapy

• Useful for moderate–severe IBS, especially with anxiety/depression.
  

9.2 Pharmacologic Management by Subtype

A. IBS-D (Diarrhea-predominant)

1. Loperamide

   • Mechanism: μ-opioid receptor agonist in gut → slows transit, improves stool consistency

   • Use: symptomatic control of diarrhea; does not improve pain.

2. Bile acid sequestrants (for suspected bile acid diarrhea)

   • Cholestyramine 4 g once or twice daily.

   • Consider if diarrhea worsens after cholecystectomy.

3. Rifaximin (for IBS-D with bloating)

   • Poorly absorbed antibiotic that modulates gut microbiota.

   • Typical course: 550 mg PO TID for 14 days; may repeat in some guidelines.

4. Eluxadoline (where available)

   • Mixed μ-opioid receptor agonist/δ antagonist; used in IBS-D but contraindicated in patients without gallbladder, pancreatitis history, etc.

5. Antispasmodics (for pain/cramping)

   • Hyoscine butylbromide, dicyclomine

   • Taken PRN before meals.

6. TCAs (Tricyclic antidepressants)

   • Amitriptyline low dose (e.g., 10–25 mg HS)

   • Helpful for pain, diarrhea (due to anticholinergic effect), and sleep.

B. IBS-C (Constipation-predominant)

1. Osmotic laxatives

   • Polyethylene glycol (PEG) – first-line.

   • Increases water in stool, softening it.

2. Soluble fiber

   • Psyllium beneficial.

   • Increase gradually to avoid gas/bloating.

3. Secretagogues

   • Linaclotide: guanylate cyclase-C agonist → ↑ intestinal fluid, ↓ visceral pain.

   • Lubiprostone: activates chloride channels → ↑ intestinal secretion (often used in women).

4. SSRIs

   • May help if constipation + mood symptoms (increase motility, improve pain).

C. IBS-M (Mixed)

• Treat according to current predominant symptom:

  • If this week: diarrhea → use IBS-D strategy

  • If constipation → IBS-C strategy

• Antispasmodic or TCA for persistent pain.

9.3 Pain & Bloating

• Pain:

  • First: antispasmodics

  • Second: low-dose TCA

• Bloating:

  • Diet (low FODMAP)

  • Rifaximin course

  • Evaluate for SIBO, lactose intolerance if persistent.

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10. Prognosis

• IBS is chronic and relapsing, but non-progressive:

  • Does not lead to cancer, IBD, or structural damage.

• Many patients improve over time with:

  • Education

  • Diet and lifestyle adjustment

  • Targeted pharmacologic therapy

However, it can significantly impact quality of life, work, mood, and relationships, so supportive care is important.

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11. IBS in Exams – High-Yield Points

1. Functional disorder: normal labs, colonoscopy, imaging.

2. Rome IV criteria: abdominal pain + relation to defecation + change stool frequency/form.

3. Red flags → NOT IBS → do colonoscopy/imaging.

4. Management:

   • Always start with education + diet + lifestyle.

   • IBS-D: loperamide, rifaximin, bile acid binders, ± TCA.

   • IBS-C: PEG, psyllium, linaclotide/lubiprostone.

   • Pain: antispasmodics → TCA.

5. Psychological component is important; CBT improves symptoms.