Gastroenterology" Inflammatory Bowel Disease

• Basics: What is IBD? | Diagnosing IBD
• Ulcerative colitis: Ulcerative Colitis | Treating Ulcerative Colitis
• Crohn's disease: Crohn's Disease | Treating Crohn's Disease | Perianal Crohn's Disease
• Drugs: Aminosalicylates and Steroids | Immunomodulators | Biologics and Small Molecules | Before Starting Immunosuppression
• Beyond drugs: Surgery in IBD | Extra-intestinal Features | Long-term Care and Cancer Surveillance | IBD in Pregnancy
• Other colitis: Microscopic Colitis | Other Causes of Colitis
• Revision: Drug Reference Table | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🔥 Inflammatory bowel disease (IBD) - ulcerative colitis and Crohn's disease - is lifelong inflammation of the gut, usually starting in young adults. Modern treatment aims not just to control symptoms but to heal the bowel lining, which prevents complications, surgery and cancer.
Your four questions for every patient: Is this UC or Crohn's, and where and how severe is it? Is it really active IBD, or infection, IBS or a drug side effect? Is the current treatment working, or does it need stepping up? Are bones, vaccinations, cancer surveillance and steroid exposure being looked after?

What is IBD?

The basics:

• An abnormal immune response to gut bacteria in genetically susceptible people.
• About 1 in 125 people in the UK have IBD.
• Peak onset 15–30 years, with a smaller peak at 50–70.
• Family history is a risk (NOD2 gene in Crohn's).
• Smoking makes Crohn's worse but appears to protect against UC (UC often starts after stopping smoking).

UC or Crohn's?

About 1 in 10 people with colitis can't be classified - "IBD unclassified".

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Diagnosing IBD

In primary care (lower GI symptoms):

• FIT first if cancer is possible (see the Bowel Disorders chapter).
• Faecal calprotectin (NICE DG11) - a protein released by inflamed bowel. It helps tell IBD from IBS in adults with new symptoms when cancer isn't suspected.
  • Under 100 µg/g - IBD unlikely; manage as IBS if it fits.
  • 100–250 µg/g - borderline: stop NSAIDs and repeat in a few weeks.
  • Over 250 µg/g - refer to gastroenterology.
• Bloods: FBC (anaemia, raised platelets), CRP, albumin, ferritin, B12, folate, coeliac serology.
• Stool culture and C. difficile - always exclude infection.

In secondary care:

• Ileocolonoscopy with biopsies - the key test.
• MRI enterography or small bowel ultrasound - to assess the small bowel in Crohn's.
• Capsule endoscopy - if small bowel Crohn's is suspected and there is no stricture.
• Pelvic MRI - perianal fistulas.
• OGD - upper GI symptoms in Crohn's.
• In acute severe disease, a flexible sigmoidoscopy is safer than full colonoscopy.

💡 Clinical Pearl: Faecal calprotectin is also used to monitor IBD. A rising level can show a flare coming before symptoms appear, and a normal level helps show that symptoms are due to IBS overlap rather than active IBD.

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Ulcerative Colitis

Extent (Montreal classification):

• Proctitis (E1) - rectum only.
• Left-sided colitis (E2) - up to the splenic flexure.
• Extensive colitis (E3) - beyond the splenic flexure (pancolitis).

Symptoms:

• Bloody diarrhoea with mucus.
• Urgency and tenesmus (feeling of needing to go even when empty).
• Night-time stools.
• Crampy lower abdominal pain.
• Proctitis may cause constipation with blood and mucus.

Severity - Truelove and Witts:

• Mild: Under 4 stools a day, small amounts of blood, systemically well.
• Moderate: 4–6 stools a day, minimal systemic upset.
• Severe: 6 or more bloody stools a day plus any of: pulse over 90, temperature over 37.8 °C, Hb under 105 g/L, ESR over 30 mm/h (or CRP over 30 mg/L).

⚠️ Safety Pearl: Acute severe UC is a medical emergency needing admission, IV steroids and early surgical review - see the Gastroenterology Emergencies chapter. Always check for C. difficile and CMV.

Endoscopy: Continuous inflammation from the rectum upwards - red, granular, friable lining that bleeds on contact; ulcers; pseudopolyps in long-standing disease.

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Treating Ulcerative Colitis

Goal: Remission without steroids, with a healed lining (mucosal healing).

Inducing remission - mild to moderate UC (NICE NG130, BSG 2025):

• Proctitis:
  • Mesalazine suppository 1 g daily - topical treatment works best here.
  • Add oral mesalazine if not enough.
  • Topical steroids if mesalazine is not tolerated.
• Left-sided or extensive colitis:
  • High-dose oral mesalazine (e.g. 2.4–4.8 g once daily) plus mesalazine enemas.
  • Once-daily dosing helps adherence.
• No response in 2–4 weeks, or more severe:
  • Oral prednisolone 40 mg daily, reducing by 5 mg a week over about 8 weeks.
  • Or budesonide MMX (9 mg daily) for mild to moderate disease (fewer side effects).
• Severe: Admit - IV hydrocortisone 100 mg four times daily or methylprednisolone 60 mg daily; rescue with infliximab or ciclosporin; colectomy if no response.

Maintaining remission:

• Mesalazine long-term (at least 2 g daily for extensive disease); topical for proctitis.
• Thiopurine (azathioprine or mercaptopurine) if the patient:
  • needs 2 or more steroid courses a year, or
  • relapses when steroids are reduced (steroid-dependent).
• Advanced therapy (biologics or small molecules) for moderate to severe UC that doesn't respond to conventional treatment.

Steroids are for induction only, never for maintenance. Steroid dependence, or more than one course a year, means treatment needs stepping up.

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Crohn's Disease

Where it occurs:

• Ileocaecal (about 40%).
• Colon only (about 30%).
• Small bowel only (about 30%).
• Upper GI (uncommon).
• Perianal disease (up to a third).

Behaviour (changes over time):

• Inflammatory.
• Stricturing - narrowing, causing colicky pain, bloating and obstruction.
• Penetrating - fistulas (to bowel, bladder, vagina or skin) and abscesses.

Symptoms:

• Abdominal pain (often right iliac fossa), diarrhoea (blood is less common than in UC).
• Weight loss, fatigue, fever.
• Mouth ulcers.
• Perianal pain, discharge or swelling.
• Children: growth failure and delayed puberty.
• A right iliac fossa mass.

Malabsorption after ileal disease or resection:

• B12 deficiency.
• Bile acid diarrhoea.
• Gallstones.
• Oxalate kidney stones.

Endoscopy and imaging:

• Patchy deep ulcers, "cobblestone" appearance, skip lesions.
• On imaging: thickened bowel and strictures ("string sign").

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Treating Crohn's Disease

Everyone:

• Stop smoking - the single most effective lifestyle change.
• Dietitian review.
• Correct anaemia and nutrition.
• Check vitamin D and bone health.

Inducing remission (NICE NG129, BSG 2025):

• Prednisolone 40 mg daily, reducing over about 8 weeks.
• Budesonide 9 mg daily - for mild to moderate ileocaecal disease (fewer side effects, less effective).
• Exclusive enteral nutrition (liquid diet only for 6–8 weeks) - first-line in children; avoids steroids and helps growth.
• Mesalazine is not effective in Crohn's.
• Moderate to severe, or high-risk disease - start advanced therapy early (e.g. anti-TNF), often with an immunomodulator. Early treatment prevents strictures and fistulas.
• High-risk features:
  • Young age at diagnosis.
  • Extensive small bowel disease.
  • Perianal disease.
  • Deep ulcers.
  • Needing steroids at diagnosis.
  • Previous resection.

Maintaining remission:

• Azathioprine or mercaptopurine; methotrexate if thiopurines are not tolerated.
• Advanced therapy continued long-term if it was needed to get remission.
• Treat to target: Symptom relief, normal CRP and calprotectin, and mucosal healing.

Strictures:

• Inflammatory strictures may respond to medical treatment.
• Fibrotic strictures need endoscopic balloon dilatation, strictureplasty or resection.
• Low-residue diet to avoid blockage.

After surgery: Colonoscopy at 6 months to check for recurrence at the join (Rutgeerts score); start treatment in high-risk patients.

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Perianal Crohn's Disease

• Features:
  • Skin tags.
  • Fissures (often painless or in unusual places).
  • Fistulas and abscesses.
  • Anal strictures.
• Assess with: Pelvic MRI and examination under anaesthetic.
• Treatment - joint medical and surgical care:
  • Drain any abscess first - never start immunosuppression with an undrained abscess.
  • Seton (a loose thread through the fistula to keep it draining).
  • Antibiotics - metronidazole or ciprofloxacin.
  • Anti-TNF (infliximab is the most studied) plus a thiopurine for maintenance.
  • Some need a defunctioning stoma or proctectomy.
• Rectovaginal fistulas are especially hard to treat.

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Aminosalicylates and Steroids

5-aminosalicylates (5-ASA) - mesalazine (also sulfasalazine, balsalazide, olsalazine):

• The mainstay in mild to moderate UC, for both induction and maintenance; may also lower colorectal cancer risk.
• Side effects:
  • Headache, nausea, diarrhoea (rarely a paradoxical flare).
  • Interstitial nephritis - check U&E before starting, then periodically (at least yearly).
  • Rare blood disorders - report sore throat, fever or bruising.
  • Pancreatitis.
  • Pericarditis or myocarditis.
• Sulfasalazine: More side effects - rash, low sperm count (reversible), blood disorders, orange urine. Used if joint disease is present too.
• Different brands release in different parts of the gut - prescribe by brand.

Corticosteroids:

• Good for inducing remission; useless for maintenance.
• Prednisolone 40 mg, tapering over about 8 weeks.
• Budesonide - mostly broken down by the liver (fewer systemic effects). Used for ileocaecal Crohn's (controlled-release), UC (MMX form) and microscopic colitis.
• Protect bones: Calcium and vitamin D during courses; DEXA scan if courses are repeated or the patient is at risk.
• Other harms:
  • Diabetes.
  • Infection.
  • Mood change.
  • Cataracts.
  • Adrenal suppression - steroid emergency card if long courses.
• Steroid-dependent (unable to reduce below 10 mg prednisolone within 3 months without relapse) or steroid-refractory disease means stepping up treatment.

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Immunomodulators

Thiopurines - azathioprine (2–2.5 mg/kg/day) and mercaptopurine (1–1.5 mg/kg/day):

• Use: Steroid-sparing maintenance in UC and Crohn's; with anti-TNF to reduce antibody formation.
• Slow to work (8–12 weeks or more).
• Before starting: Check TPMT activity (and NUDT15 where available). Low activity means a high risk of severe bone marrow suppression - use a lower dose or avoid.
• Monitoring: FBC and LFTs frequently for the first few months, then every 3 months. Drug metabolite levels guide dosing.
• Side effects:
  • Nausea and flu-like symptoms.
  • Pancreatitis (early - stop permanently).
  • Bone marrow suppression.
  • Liver toxicity.
  • Infections.
• Long-term risks:
  • Non-melanoma skin cancer - sun protection and skin checks.
  • Lymphoma (small absolute risk).
  • Cervical dysplasia - keep up cervical screening.
  • Severe primary EBV infection in EBV-negative young men.
• Interaction: Allopurinol raises thiopurine levels dangerously. It is sometimes used deliberately with a quarter-dose thiopurine, under specialist care only.

Methotrexate:

• Used in Crohn's disease: 25 mg once weekly by injection for induction, then 15 mg weekly.
• Folic acid 5 mg weekly, on a different day.
• Monitor FBC and LFTs.
• Teratogenic - effective contraception, and stop before trying to conceive.
• Prescribing errors (daily instead of weekly) can be fatal.

Ciclosporin: IV rescue therapy in acute severe UC. Check magnesium, cholesterol, BP and kidney function (risk of seizures and kidney damage).

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Biologics and Small Molecules

"Advanced therapies" are used for moderate to severe IBD that doesn't respond to conventional drugs, or as early treatment in high-risk Crohn's. The choice depends on disease type, safety, the patient's preference (infusion, injection or tablet) and cost (biosimilars).

• Anti-TNF:
  • Infliximab (IV 5 mg/kg at weeks 0, 2 and 6, then every 8 weeks; subcutaneous versions are available) and adalimumab (subcutaneous).
  • Used in UC and Crohn's, including perianal fistulas.
  • Often given with a thiopurine to reduce antibody formation.
  • Risks: Serious infection, TB reactivation, infusion reactions, psoriasis-like rash, drug-induced lupus, demyelination. Avoid in moderate to severe heart failure.
• Vedolizumab:
  • Blocks white cell migration into the gut only ("gut-selective").
  • Good safety profile - useful in older or frail people.
  • UC and Crohn's.
• IL-12/23 and IL-23 blockers:
  • Ustekinumab, risankizumab, mirikizumab, guselkumab.
  • IV induction, then subcutaneous injections.
  • Generally low infection risk.
• JAK inhibitors (tablets):
  • Tofacitinib and filgotinib (UC), upadacitinib (UC and Crohn's).
  • Work fast.
  • MHRA warning: In people over 65, smokers, and those with cardiovascular or cancer risk factors, use only if there is no suitable alternative.
  • Risks: Major cardiovascular events, VTE, cancer, infection, shingles (vaccinate), raised lipids.
  • Avoid in pregnancy.
• S1P receptor modulators (tablets):
  • Ozanimod and etrasimod (UC).
  • They keep lymphocytes in the lymph nodes.
  • Check first: ECG (they cause bradycardia and heart block), eye examination for macular oedema in people with diabetes or uveitis, and LFTs.
  • Avoid in pregnancy.
• Therapeutic drug monitoring:
  • Check drug levels and antibodies (especially for anti-TNF) if response is lost.
  • Low level, no antibodies - increase the dose.
  • Antibodies - switch drug.
  • Good level but still active - switch to a different drug class.

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Before Starting Immunosuppression

• Screen for infections:
  • TB - history, chest X-ray, IGRA. Treat latent TB first.
  • Hepatitis B (surface antigen and core antibody), hepatitis C, HIV.
  • Varicella zoster immunity.
  • EBV status (before thiopurines in young men).
• Vaccinations:
  • Pneumococcal, yearly influenza, COVID-19.
  • Shingrix (non-live shingles vaccine) where eligible - especially before JAK inhibitors.
  • HPV.
  • Live vaccines (e.g. yellow fever, MMR, BCG, oral typhoid) must be given before immunosuppression starts, or avoided while on it.
• Other checks: Cervical screening up to date; skin checks; contraception and pregnancy plans.
• Patient education: Report fever or infection early. Have a "sick day" plan, and an IBD helpline number.

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Surgery in IBD

Ulcerative colitis:

• When surgery is needed:
  • Acute severe UC that fails to respond to rescue therapy.
  • Toxic megacolon; perforation.
  • Chronic disease that doesn't respond to drugs.
  • Dysplasia or cancer.
• Emergency: Subtotal colectomy with ileostomy (rectum left for later).
• Elective options:
  • Proctocolectomy with permanent ileostomy.
  • Or ileal pouch–anal anastomosis (an "IPAA" or J-pouch) - 4–8 bowel motions a day afterwards.
• Pouchitis: Inflammation of the pouch - frequency, urgency, pain. Treat with ciprofloxacin or metronidazole for 2 weeks.

Crohn's disease:

• Most patients need surgery at some point.
• Indications: Strictures, fistulas and abscesses, failure of medical treatment, or as an alternative to long-term drugs in limited ileocaecal disease (early ileocaecal resection is a reasonable option).
• Principles:
  • Bowel-sparing - limited resections and strictureplasty, because disease recurs.
  • Repeated resections risk short bowel syndrome.
• Abscesses: Drain (often radiologically) and give antibiotics before surgery.
• Nutrition and stopping steroids before planned surgery reduce complications.

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Extra-intestinal Features

⚠️ Safety Pearl: Every inpatient with an IBD flare needs VTE prophylaxis (LMWH), even with rectal bleeding. Bleeding is not a reason to withhold it.

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Long-term Care and Cancer Surveillance

Colorectal cancer surveillance (BSG):

• Who: UC beyond the rectum, or Crohn's colitis involving more than one segment of colon. Proctitis alone does not need surveillance.
• When to start: Colonoscopy 8 years after symptoms began; from diagnosis in PSC.
• How often (based on risk):
  • Yearly: PSC, extensive colitis with moderate or severe inflammation, a stricture or dysplasia in the last 5 years, or a first-degree relative with colorectal cancer under 50.
  • Every 3 years: Extensive colitis with mild inflammation, post-inflammatory polyps, or a first-degree relative diagnosed at 50 or over.
  • Every 5 years: Everyone else needing surveillance.
• Use chromoendoscopy (dye spray) or high-definition colonoscopy, ideally when the disease is in remission.
• Dysplasia: Remove visible lesions endoscopically; colectomy for invisible or multifocal dysplasia.

Routine care checklist:

• Anaemia - check FBC and ferritin. IV iron if Hb is under 100 g/L, active disease, or intolerance of oral iron.
• Bone health - vitamin D, DEXA where indicated.
• Vaccinations and skin and cervical screening for people on immunosuppression.
• B12 after ileal resection.
• Smoking cessation.
• Mental health - anxiety and depression are common.
• IBS-type symptoms in remission - check calprotectin before escalating treatment.
• Avoid NSAIDs (they can trigger flares); avoid opioids and antimotility drugs in active colitis (risk of toxic megacolon).

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IBD in Pregnancy

• Plan ahead: The best outcomes come when the disease is in remission at conception. Active disease raises the risk of miscarriage, preterm birth and low birth weight - this is more dangerous than most drugs.
• Continue (generally safe):
  • Mesalazine.
  • Sulfasalazine (with folic acid 5 mg).
  • Thiopurines.
  • Steroids for flares.
  • Anti-TNF, vedolizumab and ustekinumab - usually continued throughout, sometimes with timing adjusted in the third trimester.
• Stop before conception:
  • Methotrexate (teratogenic - stop at least 3–6 months before; check current advice).
  • JAK inhibitors and S1P modulators (avoid).
• Babies exposed to biologics in late pregnancy: Avoid live vaccines (e.g. rotavirus, BCG) until specialist advice allows - usually not in the first 6–12 months. Other childhood vaccines are given as normal.
• Delivery: Usually vaginal. Caesarean is advised for active perianal disease or an ileal pouch.
• Breastfeeding: Compatible with most IBD drugs (not methotrexate or small molecules).
• Give VTE prophylaxis in flares and postpartum as per obstetric risk.

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Microscopic Colitis

What it is: Inflammation seen only under the microscope - the colon looks normal at colonoscopy. There are two types:

• Collagenous colitis - a thick collagen band.
• Lymphocytic colitis - many lymphocytes in the lining.

Who gets it:

• Women over 50.
• Smokers.
• People with other autoimmune diseases (coeliac, thyroid).
• Drug triggers: PPIs (especially lansoprazole), NSAIDs, SSRIs (e.g. sertraline), statins, beta-blockers, acarbose.

Symptoms:

• Chronic watery diarrhoea (not bloody), often at night.
• Urgency and incontinence.
• Mild weight loss.

Diagnosis:

• Colonoscopy with biopsies from the right and left colon - always biopsy in chronic diarrhoea, even if the colon looks normal.
• Faecal calprotectin can be normal or raised.
• Check coeliac serology.

Treatment:

• Stop trigger drugs; stop smoking.
• Budesonide 9 mg daily for 8 weeks - very effective.
• Relapse is common - low-dose budesonide maintenance (e.g. 6 mg).
• Loperamide for mild disease.
• Consider coexisting bile acid diarrhoea.
• Refractory cases: specialist immunosuppression or biologics.

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Other Causes of Colitis

• Infective colitis:
  • Campylobacter, Salmonella, Shigella, E. coli O157 (bloody diarrhoea, risk of haemolytic uraemic syndrome - avoid antibiotics and antimotility drugs).
  • C. difficile; CMV (immunosuppressed); amoebiasis (travel).
  • Always send stool samples before diagnosing a first episode of IBD or a flare.
• Ischaemic colitis:
  • Older people with vascular disease.
  • Sudden crampy left-sided pain followed by bloody diarrhoea.
  • The splenic flexure is a "watershed" area.
  • CT shows thickened bowel; "thumbprinting" on X-ray.
  • Most settle with supportive care. Peritonitis or gangrene needs surgery.
• Radiation proctitis: Bleeding months to years after pelvic radiotherapy (prostate, cervix). Treated with sucralfate enemas, argon plasma coagulation, or hyperbaric oxygen.
• Drug-induced colitis:
  • Immune checkpoint inhibitors (ipilimumab, nivolumab, pembrolizumab) - diarrhoea in cancer patients. Grade it, exclude infection, and give steroids early; infliximab or vedolizumab if refractory.
  • NSAIDs.
  • Mycophenolate.
• Diversion colitis: Inflammation in a bowel segment cut off from the faecal stream (after a stoma).
• Behçet's disease: Ileocaecal ulcers with mouth and genital ulcers.
• Diverticular colitis: Segmental colitis around diverticula.

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Drug Reference Table

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Spot the Diagnosis

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Exam-style Scenarios

1. A 28-year-old woman has 3 weeks of bloody diarrhoea 3 times a day. Sigmoidoscopy shows inflammation up to 15 cm.
Answer: Mild proctitis / proctosigmoiditis (UC).

• Send stool cultures and C. difficile.
• Mesalazine suppository 1 g daily (or enema), plus oral mesalazine if needed.
• Oral prednisolone if no response in 2–4 weeks.

2. A man with UC needed three courses of prednisolone this year.
Answer: Steroid-dependent or frequently relapsing UC - step up treatment.

• Start azathioprine (check TPMT first) or an advanced therapy.
• Check bone health; give calcium and vitamin D.
• Check calprotectin and endoscopic activity to guide treatment.

3. A 22-year-old with ileal Crohn's has a perianal swelling and fever.
Answer: Perianal abscess.

• Pelvic MRI and surgical drainage (examination under anaesthetic, seton if there is a fistula).
• Antibiotics.
• Then anti-TNF (e.g. infliximab) with a thiopurine once sepsis is controlled.

4. A 30-year-old with Crohn's is due to start infliximab.
Answer: Screen and protect first.

• Chest X-ray and IGRA for TB; hepatitis B, hepatitis C and HIV tests; varicella immunity.
• Vaccinate (pneumococcal, influenza, COVID-19); give live vaccines before starting if needed.
• Advise her to report infections early.

5. A woman with UC in remission on azathioprine and mesalazine wants to get pregnant.
Answer: Continue both drugs - remission at conception is the priority.