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.

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.)

3. Pathophysiology (Why IBS Happens)

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

Visceral hypersensitivity
- The intestines are “too sensitive” → normal gas or stool distension causes pain.
Abnormal gut motility
- Accelerated transit → diarrhea-predominant IBS (IBS-D)
- Delayed transit → constipation-predominant IBS (IBS-C)
Brain–gut axis dysregulation
- Stress, anxiety, and psychological factors affect gut motility and sensation via neural and hormonal pathways.
Post-infectious changes
- Some patients develop IBS after gastroenteritis (post-infectious IBS).
- Thought due to persistent low-grade inflammation, altered microbiota.
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.

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

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:

Related to defecation (pain better or worse with bowel movement)
Associated with change in stool frequency
Associated with change in stool form (appearance)

Symptoms should start ≥6 months before diagnosis.

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.

7. Approach to Diagnosis

7.1 Basic Evaluation

IBS is a clinical diagnosis after:

History fitting Rome IV criteria
Absence of red flags
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

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.

9. Management of IBS

Key Principles

Confirm diagnosis and reassure: “This is real, but not dangerous, not cancer.”
Identify subtype (IBS-C, IBS-D, IBS-M).
Lifestyle and diet first; pharmacotherapy based on predominant symptom.
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

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.
Fiber
- Soluble fiber (psyllium) is helpful, especially in IBS-C.
- Insoluble fiber (bran) may worsen bloating and pain.
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)

Loperamide
- Mechanism: μ-opioid receptor agonist in gut → slows transit, improves stool consistency
- Use: symptomatic control of diarrhea; does not improve pain.
Bile acid sequestrants (for suspected bile acid diarrhea)
- Cholestyramine 4 g once or twice daily.
- Consider if diarrhea worsens after cholecystectomy.
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.
Eluxadoline (where available)
- Mixed μ-opioid receptor agonist/δ antagonist; used in IBS-D but contraindicated in patients without gallbladder, pancreatitis history, etc.
Antispasmodics (for pain/cramping)
- Hyoscine butylbromide, dicyclomine
- Taken PRN before meals.
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)

Osmotic laxatives
- Polyethylene glycol (PEG) – first-line.
- Increases water in stool, softening it.
Soluble fiber
- Psyllium beneficial.
- Increase gradually to avoid gas/bloating.
Secretagogues
- Linaclotide: guanylate cyclase-C agonist → ↑ intestinal fluid, ↓ visceral pain.
- Lubiprostone: activates chloride channels → ↑ intestinal secretion (often used in women).
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.

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.

11. IBS in Exams – High-Yield Points

Functional disorder: normal labs, colonoscopy, imaging.
Rome IV criteria: abdominal pain + relation to defecation + change stool frequency/form.
Red flags → NOT IBS → do colonoscopy/imaging.
Management:
- Always start with education + diet + lifestyle.
- IBS-D: loperamide, rifaximin, bile acid binders, ± TCA.
- IBS-C: PEG, psyllium, linaclotide/lubiprostone.
- Pain: antispasmodics → TCA.
Psychological component is important; CBT improves symptoms.