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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Continuous mucosal inflammation starting at the rectum and extending proximally — NEVER has skip lesions
- Cardinal symptom: bloody diarrhoea with mucus and urgency
- Truelove & Witts: mild (<4 stools/day, no systemic upset), moderate (4–6), severe (>6 + systemic features)
- Maintenance: 5-ASA (mesalazine) — topical (rectal) + oral depending on extent
- Acute severe colitis is a medical emergency: IV hydrocortisone, escalate to ciclosporin/infliximab if no response by day 3, surgery (subtotal colectomy) if failing rescue therapy
- Unlike Crohn's, colectomy is curative — but patient loses the colon
Overview
Ulcerative colitis is a chronic inflammatory bowel disease characterised by diffuse, continuous, superficial (mucosal and submucosal) inflammation of the colon. It invariably involves the rectum and may extend proximally in a continuous fashion to involve part or all of the colon. Disease extent is classified as proctitis (rectum only), left-sided colitis (up to splenic flexure), or extensive/pancolitis (beyond splenic flexure). Unlike Crohn's disease, UC does not produce skip lesions, granulomata, or transmural inflammation.
Epidemiology
UC prevalence in the UK is approximately 240 per 100,000, slightly more common than Crohn's. Peak incidence is 15–25 years with a smaller second peak at 55–65 years. Unlike Crohn's, smoking is protective — UC often presents or flares after smoking cessation. Appendicectomy appears protective. Family history is a risk factor. There is a significant long-term risk of colorectal cancer, particularly with extensive colitis and disease duration >10 years.
Clinical Features
Symptoms
Bloody diarrhoea — the cardinal symptom
Mucus in stool
Urgency and tenesmus (rectal involvement)
Abdominal cramping, typically left-sided
Fatigue
Passing >6 bloody stools/day with systemic features (severe colitis)
Abdominal distension with reduced bowel sounds (toxic megacolon)
Signs
Left iliac fossa tenderness
Pallor (anaemia from chronic blood loss)
Tachycardia, fever, dehydration (severe/acute flare)
Extraintestinal: erythema nodosum, pyoderma gangrenosum, anterior uveitis, large joint arthritis, primary sclerosing cholangitis
Abdominal distension, absent bowel sounds (toxic megacolon — surgical emergency)
Investigations
First-line
BloodsFBC (anaemia, thrombocytosis), CRP/ESR, albumin (low = severe disease), U&Es, LFTs
Faecal calprotectinMarkedly elevated in active IBD — useful for diagnosis and monitoring response to treatment
Stool MC&S + C. difficile toxinMandatory to exclude infective cause before diagnosing or treating IBD flare
Second-line
Flexible sigmoidoscopy / colonoscopy with biopsiesGold standard. Macroscopy: continuous inflammation from rectum, erythema, friability, ulceration, pseudopolyps. Histology: mucosal/submucosal inflammation, crypt abscesses, goblet cell depletion
AXRIn acute severe colitis: exclude toxic megacolon (transverse colon diameter >6 cm), look for mucosal islands
Specialist
CT abdomenIf perforation or toxic megacolon suspected
pANCA / ASCApANCA positive in ~65% UC; ASCA positive in ~60% Crohn's — supportive but not diagnostic
MRCPIf LFTs deranged — screen for primary sclerosing cholangitis (associated with UC)
1
Inducing remission — mild-to-moderate flare
- Proctitis: topical (rectal) mesalazine (5-ASA) suppository ± topical steroid
- Left-sided: rectal mesalazine foam/enema + oral mesalazine
- Extensive: oral mesalazine (≥2.4 g/day) + topical mesalazine
- If 5-ASA alone insufficient: add oral prednisolone 40 mg tapered over 8 weeks
2
Maintaining remission
- 5-ASA (mesalazine) is first-line maintenance for all extents
- Topical mesalazine for proctitis; oral + topical for more extensive disease
- If frequent relapses despite 5-ASA: add azathioprine or mercaptopurine
- Steroids must NOT be used for maintenance
3
Acute severe colitis (Truelove & Witts: >6 bloody stools/day + systemic features)
- Hospital admission — this is a medical emergency
- IV hydrocortisone 100 mg QDS
- IV fluids, VTE prophylaxis (LMWH), stool chart, twice-daily bloods
- Assess response at day 3 (Travis criteria): if stool frequency >8/day or CRP >45 → failing IV steroids
- Rescue therapy: IV ciclosporin OR infliximab (discuss with specialist and surgical team)
- If failing rescue therapy → subtotal colectomy with end ileostomy
4
Surgery
- Subtotal colectomy is CURATIVE — removes the entire colon
- Indications: acute severe colitis failing medical therapy, toxic megacolon, perforation, dysplasia/cancer
- Options: proctocolectomy + ileal pouch-anal anastomosis (IPAA/J-pouch) or permanent ileostomy
- J-pouch complication: pouchitis (treat with metronidazole/ciprofloxacin)
Complications
- Toxic megacolon: Transverse colon >6 cm with systemic toxicity — risk of perforation and death. Surgical emergency
- Colorectal cancer: Risk increases with disease duration (>10 years) and extent (pancolitis > left-sided). Surveillance colonoscopy from 10 years post-diagnosis
- Primary sclerosing cholangitis (PSC): Associated with UC in ~5% — raised ALP, beaded bile ducts on MRCP
- VTE: IBD is an independent risk factor — prophylaxis during hospital admission
- Anaemia: Iron deficiency from chronic blood loss; B12/folate from malabsorption or methotrexate
- Osteoporosis: Chronic steroid use
UKMLA Exam Tips
- 1UC = bloody diarrhoea + continuous inflammation starting at rectum. Crohn's = non-bloody diarrhoea + skip lesions + mouth to anus
- 2Truelove & Witts severe: >6 bloody stools/day + ANY of: pulse >90, temp >37.8°C, Hb <105, ESR >30
- 3Acute severe colitis: assess response to IV steroids at DAY 3 — this is the key decision point for rescue therapy
- 4Toxic megacolon = transverse colon >6 cm on AXR. Do NOT perform colonoscopy — perforation risk
- 5PSC is specifically associated with UC (not Crohn's) — always check LFTs. PSC also increases cholangiocarcinoma risk
- 6Mesalazine (5-ASA) can INDUCE and MAINTAIN remission in UC — unlike Crohn's where it has a limited role
- 7Colectomy CURES UC — this is a key differentiator from Crohn's where surgery is not curative
practicetest your knowledge on ulcerative colitisApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — gastroenterology and beyond.
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