Overview
Inflammatory Bowel Disease (IBD)
1. Clinical Overview
Summary
Inflammatory Bowel Disease (IBD) comprises two main conditions: Ulcerative Colitis (UC) and Crohn's Disease (CD). Both are chronic, relapsing-remitting inflammatory disorders of the gastrointestinal tract. Ulcerative Colitis is characterised by continuous mucosal inflammation starting from the rectum and extending proximally in a contiguous pattern. Crohn's Disease can affect any part of the GI tract (Mouth to Anus, most commonly Terminal Ileum) with skip lesions and transmural inflammation (leading to strictures, fistulae, abscesses). Treatment is stepwise escalation: 5-ASA (Aminosalicylates) are first-line for UC; Corticosteroids induce remission in flares; Thiopurines (Azathioprine/Mercaptopurine) and Methotrexate maintain remission; Biologics (Anti-TNF, Vedolizumab, Ustekinumab, JAK inhibitors) are used for moderate-severe or refractory disease. Acute Severe Colitis is a medical emergency requiring hospitalisation and IV steroids. Surgery may be curative in UC (Colectomy) but not in Crohn's. [1,2]
Clinical Pearls
UC = Continuous, Mucosal, Always Starts at Rectum: Think "Rectum is Certain" in UC. Crohn's = Skip lesions, Transmural, Anywhere.
"Bloody Diarrhoea" = UC, "Abdominal Pain + Diarrhoea" = Crohn's: Classic presenting symptoms differ. UC more likely to have blood; Crohn's more likely to have pain/mass.
5-ASA is Cornerstone of UC: Mesalazine (Oral + Rectal) is first-line induction and maintenance for Ulcerative Colitis. NOT effective for Crohn's.
Toxic Megacolon = Emergency: Dilated colon (>6cm on AXR) + Systemic toxicity. Risk of perforation. May need emergency colectomy.
2. Epidemiology
Demographics
| Factor | Ulcerative Colitis | Crohn's Disease |
|---|---|---|
| Age of Onset | Bimodal: 15-30 and 50-70 years | Bimodal: 15-30 and 50-70 years |
| Sex | Slight Male predominance | Slight Female predominance |
| Geography | More common in Developed countries, Northern latitudes | Same |
| Smoking | Protective (UC worse if stop smoking) | Worsens Crohn's |
Risk Factors
- Genetics: Family history. Multiple susceptibility genes (NOD2/CARD15 for Crohn's).
- Environment: Western diet, Hygiene hypothesis, Antibiotics.
- Smoking: UC – Protective. Crohn's – Harmful.
- Appendectomy: Protective for UC.
3. Pathophysiology
Differences Between UC and Crohn's
| Feature | Ulcerative Colitis | Crohn's Disease |
|---|---|---|
| Location | Colon only. Always involves Rectum. May extend to Pancolitis. | Any part of GI tract (Mouth to Anus). Terminal Ileum most common. |
| Pattern | Continuous (No skip lesions). | Skip Lesions (Normal bowel between affected segments). |
| Depth | Mucosal (Superficial). | Transmural (Full thickness). |
| Histology | Crypt abscesses, Goblet cell depletion. Pseudopolyps. | Non-Caseating Granulomas (~30%). Transmural inflammation. |
| Complications | Toxic Megacolon, Haemorrhage, Colorectal Cancer (Long-standing Pancolitis). | Strictures, Fistulae (Enteroenteric, Enterocutaneous, Perianal), Abscesses, Obstruction. |
| Surgery | Curative (Colectomy). | NOT curative (Recurrence common). |
Underlying Mechanism
- Genetic Susceptibility: Polygenic. NOD2/CARD15 (Crohn's).
- Environmental Trigger: Dysbiosis, Infection, Diet.
- Immune Dysregulation: Aberrant T-cell response to gut flora. Loss of tolerance.
- Chronic Inflammation: Cytokine-driven (TNF-α, IL-12, IL-23).
4. Differential Diagnosis
| Condition | Key Features |
|---|---|
| Ulcerative Colitis | Bloody Diarrhoea. Continuous from Rectum. Mucosal. No granulomas. |
| Crohn's Disease | Abdominal pain, Non-bloody diarrhoea, Weight loss. Skip lesions. Transmural. Granulomas. Fistulae. |
| Infectious Colitis | Acute onset. Stool culture positive. Travel history. C. difficile (Antibiotic history). |
| Ischaemic Colitis | Elderly. Sudden abdominal pain. Bloody diarrhoea. "Watershed" areas. |
| Microscopic Colitis (Collagenous/Lymphocytic) | Watery diarrhoea. Normal colonoscopy. Diagnosis on biopsy. |
| Colorectal Cancer | Older age. Change in bowel habit. Rectal bleeding. Weight loss. Iron deficiency anaemia. |
| IBS | No red flags (No weight loss, No bleeding, No anaemia). Abdominal pain related to defecation. Normal investigations. |
| Diverticulitis | Left iliac fossa pain. Fever. CT shows diverticula + Inflammation. |
| Coeliac Disease | Diarrhoea, Malabsorption. Anti-TTG positive. Duodenal biopsy. |
5. Clinical Presentation
Ulcerative Colitis
| Feature | Notes |
|---|---|
| Bloody Diarrhoea | Cardinal symptom. Mucus. Urgency. Tenesmus. |
| Rectal Involvement (Always) | Proctitis → Left-sided Colitis → Pancolitis. |
| Systemic Symptoms | Fatigue, Weight loss, Fever (Severe disease). |
| Extraintestinal Manifestations | See below. |
Crohn's Disease
| Feature | Notes |
|---|---|
| Abdominal Pain | Common (RLQ if Terminal Ileum). Colicky. |
| Non-Bloody Diarrhoea | (Blood less common than UC). |
| Weight Loss / Malnutrition | Small bowel involvement → Malabsorption. |
| Perianal Disease | Fistulae, Abscesses, Fissures. Characteristic of Crohn's. |
| Oral Ulcers | Aphthous ulcers. |
| Strictures / Obstruction | Transmural scarring. |
| Fistulae | Enteroenteric, Enterovesical (Pneumaturia), Enterocutaneous. |
| Extraintestinal Manifestations | See below. |
Extraintestinal Manifestations (Both UC and Crohn's)
| System | Manifestations |
|---|---|
| Musculoskeletal | Peripheral Arthritis (Correlates with disease activity), Axial Spondyloarthropathy (Ankylosing Spondylitis, Sacroiliitis – Independent of disease activity). |
| Skin | Erythema Nodosum (Correlates with activity), Pyoderma Gangrenosum (Does NOT correlate). |
| Eyes | Episcleritis, Uveitis. |
| Hepatobiliary | Primary Sclerosing Cholangitis (PSC – Especially UC). Cholangiocarcinoma risk. |
| Other | Venous Thromboembolism (Hypercoagulable), Anaemia, Osteoporosis. |
6. Investigations
Blood Tests
| Test | Findings |
|---|---|
| FBC | Anaemia (Iron deficiency or Chronic disease), Leucocytosis, Thrombocytosis (Inflammation). |
| CRP / ESR | Elevated in active disease. |
| Albumin | Low if Malnutrition / Protein-losing enteropathy. |
| LFTs | May be abnormal (PSC, Drug-related). |
| Iron Studies | Iron deficiency common. |
| Vitamin Levels (B12, Folate, Vitamin D) | Crohn's (Terminal Ileum) → B12 deficiency. |
Stool Tests
| Test | Purpose |
|---|---|
| Faecal Calprotectin | Marker of intestinal inflammation. Elevated in IBD. Normal in IBS. |
| Stool Cultures / C. diff Toxin | Exclude infection (Especially during flare). |
Endoscopy (Key Diagnostic Tool)
| Procedure | Findings |
|---|---|
| Colonoscopy + Biopsies | UC: Continuous inflammation from Rectum. Mucosal erythema, Friability, Pseudopolyps. Crohn's: Skip lesions. Cobblestoning. Deep ulcers. Strictures. Granulomas on biopsy. |
| Upper GI Endoscopy / Capsule Endoscopy / MRI Enterography | For Crohn's small bowel assessment. |
Imaging
| Imaging | Purpose |
|---|---|
| AXR | Toxic Megacolon (Colon >6cm). Obstruction. |
| CT Abdomen/Pelvis | Complications (Abscess, Perforation, Stricture, Fistula). |
| MRI Enterography | Small bowel Crohn's. Active inflammation vs Fibrotic stricture. |
| Pelvic MRI | Perianal Crohn's (Fistulae, Abscesses). |
7. Management
Management Algorithm (Ulcerative Colitis)
ULCERATIVE COLITIS
↓
ASSESS SEVERITY (Truelove & Witts / Montreal)
┌───────────────────────────────────────────────┐
│ MILD: less than 4 stools/day, No systemic toxicity │
│ MODERATE: 4-6 stools, Minimal systemic signs │
│ SEVERE: >6 bloody stools + Systemic toxicity │
│ (Fever >37.8, HR >90, Hb less than 10.5, │
│ ESR >30) │
└───────────────────────────────────────────────┘
↓
TREATMENT BY SEVERITY
┌────────────────┴────────────────┐
MILD-MODERATE SEVERE (ACUTE SEVERE COLITIS)
↓ ↓
OUTPATIENT ADMIT TO HOSPITAL
5-ASA (Mesalazine) IV HYDROCORTISONE
Oral + Rectal 100mg QDS (or Methylpred)
+ VTE Prophylaxis
+ Stool Cultures (C. diff)
+ AXR (Toxic Megacolon?)
+ Surgical Review
↓
RESPONSE AT DAY 3?
┌────────────┴────────────┐
YES NO
↓ ↓
STEP DOWN RESCUE THERAPY
Oral Steroids Ciclosporin IV
+ 5-ASA Maintenance OR Infliximab IV
(If fails → Colectomy)
Ulcerative Colitis Treatment Summary
| Severity | Induction | Maintenance |
|---|---|---|
| Mild | Rectal 5-ASA (±Oral) | Oral + Rectal 5-ASA |
| Moderate | Oral 5-ASA + Oral Steroids (Prednisolone) | 5-ASA (±Thiopurine) |
| Severe | IV Steroids → Rescue (Ciclosporin/Infliximab) | Thiopurine + 5-ASA OR Biologic |
| Extensive/Refractory | Biologics (Anti-TNF, Vedolizumab, Ustekinumab, Tofacitinib) | Biologic maintenance |
Management Algorithm (Crohn's Disease)
CROHN'S DISEASE
↓
ASSESS LOCATION & SEVERITY
(Luminal, Stricturing, Penetrating/Fistulising)
↓
INDUCTION OF REMISSION
┌──────────────────────────────────────────────────────────┐
│ ILEOCAECAL MILD: Budesonide 9mg OD (Entocort) │
│ MODERATE-SEVERE: Oral Prednisolone │
│ SEVERE/REFRACTORY: IV Steroids, then Biologic │
│ (Note: 5-ASA NOT effective in Crohn's) │
└──────────────────────────────────────────────────────────┘
↓
MAINTENANCE OF REMISSION
┌──────────────────────────────────────────────────────────┐
│ THIOPURINE (Azathioprine/6-MP) │
│ OR METHOTREXATE (If Thiopurine intolerant) │
│ OR BIOLOGIC: │
│ - Anti-TNF (Infliximab, Adalimumab) │
│ - Vedolizumab (Gut-selective anti-Integrin) │
│ - Ustekinumab (Anti-IL-12/23) │
│ - Risankizumab (Anti-IL-23) │
└──────────────────────────────────────────────────────────┘
↓
PERIANAL CROHN'S
- MRI Pelvis (Assess fistulae)
- Antibiotics (Metronidazole + Ciprofloxacin)
- EUA + Seton insertion (Drain abscess)
- Anti-TNF (Infliximab for fistulising disease)
↓
SURGERY (NOT Curative in Crohn's)
- Stricturoplasty / Resection for Obstruction
- Abscess drainage
- Resection of refractory disease
Key Drug Classes
| Class | Examples | Notes |
|---|---|---|
| 5-ASA (Aminosalicylates) | Mesalazine (Pentasa, Asacol, Octasa), Sulfasalazine | First-line UC. Oral + Rectal. NOT for Crohn's. |
| Corticosteroids | Prednisolone, Hydrocortisone (IV), Budesonide (Ileal Crohn's) | Induce remission. NOT for maintenance (Side effects). |
| Thiopurines | Azathioprine, Mercaptopurine | Maintenance. TPMT testing before starting (Myelotoxicity risk). |
| Methotrexate | Methotrexate SC | Maintenance (Crohn's). Folic acid supplementation. |
| Anti-TNF | Infliximab, Adalimumab | First-line biologic for Moderate-Severe. Fistulising Crohn's. |
| Vedolizumab | Vedolizumab (IV/SC) | Gut-selective Anti-α4β7 Integrin. UC and Crohn's. |
| Ustekinumab | Ustekinumab (IV/SC) | Anti-IL-12/23. Crohn's and UC. |
| JAK Inhibitors | Tofacitinib, Filgotinib, Upadacitinib | Oral small molecules. UC (Tofacitinib). |
8. Complications
| Complication | UC | Crohn's |
|---|---|---|
| Toxic Megacolon | Yes (Emergency) | Rare |
| Colorectal Cancer | Yes (Surveillance colonoscopy) | Yes (Colonic Crohn's) |
| Stricture / Obstruction | Rare | Common (Transmural) |
| Fistulae | No | Yes (Enteroenteric, Enterovesical, Perianal) |
| Abscess | Rare | Yes |
| Perforation | Yes (Toxic Megacolon) | Yes (Transmural) |
| Primary Sclerosing Cholangitis | Yes (Strong association) | Rare |
| Malnutrition | Less common | Common (Small bowel) |
9. Prognosis and Outcomes
- Chronic Relapsing: Both UC and Crohn's are lifelong conditions with flares and remissions.
- Surgery: ~30% UC patients need Colectomy (Curative). ~50-70% Crohn's patients need surgery at some point (NOT curative – Recurrence common).
- Colorectal Cancer Risk: Increased in long-standing extensive UC/Colonic Crohn's. Surveillance colonoscopy recommended.
10. Evidence and Guidelines
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| ECCO Guidelines | European Crohn's and Colitis Organisation | Comprehensive UC and Crohn's management. |
| NICE NG129/NG130 | NICE | UC and Crohn's management pathways. |
| BSG IBD Guidelines | BSG | UK guidance. Acute Severe Colitis management. |
11. Patient and Layperson Explanation
What is IBD?
IBD (Inflammatory Bowel Disease) is a group of conditions where the gut becomes chronically inflamed. The two main types are:
- Ulcerative Colitis (UC): Affects only the large bowel (Colon), starting from the rectum.
- Crohn's Disease: Can affect any part of the digestive system, from mouth to bottom, but most often the end of the small intestine.
What are the symptoms?
- Diarrhoea (often bloody in UC)
- Abdominal pain and cramping
- Urgency to open bowels
- Tiredness
- Weight loss
How is it treated?
Treatment aims to control inflammation and prevent flares:
- Tablets (5-ASA like Mesalazine): First-line for UC.
- Steroids: For flares (Short-term).
- Immunosuppressants (Azathioprine, Methotrexate): Keep disease in check.
- Biologics (Infliximab, Adalimumab, Vedolizumab): For more severe cases.
- Surgery: Sometimes needed to remove affected bowel.
Can it be cured?
There is no cure, but with good treatment, most people with IBD can live normal, active lives with long periods of remission.
12. References
Primary Sources
- Raine T, et al. ECCO Guidelines on Therapeutics in Ulcerative Colitis. J Crohns Colitis. 2022;16(1):2-17. PMID: 34635916.
- Torres J, et al. ECCO Guidelines on Therapeutics in Crohn's Disease. J Crohns Colitis. 2020;14(1):4-22. PMID: 31711158.
13. Examination Focus
Common Exam Questions
- UC vs Crohn's Pattern: "What is the difference in distribution pattern between UC and Crohn's?"
- Answer: UC = Continuous inflammation starting from Rectum. Crohn's = Skip lesions, any part of GI tract.
- First-Line Treatment for Mild UC: "First-line treatment for mild Ulcerative Colitis?"
- Answer: 5-ASA (Mesalazine) – Oral and/or Rectal.
- Histological Feature of Crohn's: "Pathognomonic histological finding in Crohn's Disease?"
- Answer: Non-Caseating Granulomas (Present in ~30%).
- Toxic Megacolon Definition: "How is Toxic Megacolon defined on imaging?"
- Answer: Colonic dilatation >6cm on plain abdominal X-ray.
Viva Points
- Smoking in IBD: Protective in UC, Harmful in Crohn's.
- PSC Association: Primary Sclerosing Cholangitis is strongly associated with UC.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.