IBD patterns and severe colitis assessment

Inflammatory Bowel Disease, Malabsorption & Luminal Disorders

Luminal gastrointestinal conditions encompass chronic immune-mediated inflammatory bowel disease (IBD), auto-antigenic enteropathies such as coeliac disease, and functional gut-brain axis disorders including irritable bowel syndrome (IBS). Distinguishing inflammatory structural pathology from functional presentations, managing acute severe ulcerative colitis flares, and identifying extraintestinal manifestations are foundational topics for the AMC examination.

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Crohn's Disease versus Ulcerative Colitis

Inflammatory bowel disease represents a chronic, relapsing immune-mediated disorder of the gastrointestinal tract. Although both entities share systemic inflammatory pathways, their anatomical extent, depth of tissue destruction, clinical presentations, and surgical paradigms differ fundamentally.

Core Pathological and Anatomical Distinctions

• Anatomical Distribution: Crohn's Disease (CD): Any segment from mouth to anus ('gum to bum'). Terminal ileum and caecum most commonly involved ($50\%$ ileocolic).; Ulcerative Colitis (UC): Confined to the colon and rectum. Invariably involves the rectum ($> 95\%$) and extends proximally in a continuous manner.
• Continuity of Lesions: Crohn's Disease (CD): Skip lesions: Diseased intestinal segments interspersed with macroscopically normal mucosa.; Ulcerative Colitis (UC): Continuous and symmetrical: No skip areas. Proctitis (E1), left-sided colitis (E2), or pancolitis (E3).
• Depth of Inflammation: Crohn's Disease (CD): Transmural: Involves mucosa, submucosa, muscularis propria, and subserosa.; Ulcerative Colitis (UC): Mucosal and submucosal only: Muscularis and serosa spared (except in toxic megacolon).
• Macroscopic Appearance: Crohn's Disease (CD): Deep linear 'railroad' ulcers, 'cobblestone' mucosa, bowel wall thickening with luminal strictures, and mesenteric creeping fat.; Ulcerative Colitis (UC): Diffuse erythema, granular friable mucosa, superficial continuous ulceration, and pseudopolyps. Loss of haustra ('lead-pipe' colon).
• Microscopic Histology: Crohn's Disease (CD): Non-caseating epithelioid granulomas (pathognomonic, present in $30-50\%$), transmural lymphoid aggregates, fissures.; Ulcerative Colitis (UC): Crypt architectural distortion, neutrophilic crypt abscesses, cryptitis, and goblet cell mucin depletion. No granulomas.
• Perianal disease: Fistulae and abscesses favour Crohn disease, but a perianal finding alone cannot categorically exclude ulcerative colitis or an unrelated local condition.
• Smoking: Advise cessation. The epidemiological association between smoking and ulcerative colitis does not justify recommending smoking or routine nicotine patches as UC treatment.
• Definitive Surgery: Crohn's Disease (CD): Non-curative; segmental resection reserved for strictures, fistulae, or perforation. High recurrence rate.; Ulcerative Colitis (UC): Curative: Total proctocolectomy with ileal pouch-anal anastomosis (IPAA) eliminates mucosal disease.

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Extraintestinal Manifestations (EIMs)

Up to $40\%$ of patients with IBD develop systemic extraintestinal manifestations involving the skin, joints, eyes, and hepatobiliary system. For clinical practice and examinations, EIMs are divided into those that parallel bowel inflammation and those that progress independently.

Clinical Presentation of Key EIMs

1. Dermatological:
   • Erythema Nodosum: Painful, tender, erythematous, non-ulcerative subcutaneous nodules characteristically situated over the anterior pretibial surfaces. Flares correlate directly with bowel inflammation and resolve with treatment of the colitis.
   • Pyoderma Gangrenosum: Severe, rapidly destructive dermatosis initiating as an erythematous pustule or nodule that breaks down into an exquisitely painful, enlarging ulcer with violaceous, undermined, necrotic borders. Displays pathergy (exacerbation or induction by minor trauma, surgical debridement, or skin biopsy). May progress independently of bowel disease; treated with systemic corticosteroids, ciclosporin, or infliximab.
2. Musculoskeletal:
   • Peripheral Arthritis: Non-deforming, seronegative arthropathy. Type 1 (oligoarticular, affecting $< 5$ large weight-bearing joints) mirrors intestinal disease activity; Type 2 (polyarticular, symmetric small joint involvement) runs an independent course.
   • Axial Spondyloarthropathy: Ankylosing spondylitis and bilateral sacroiliitis; strongly linked to HLA-B27. Causes inflammatory back pain (morning stiffness $> 30\text{ minutes}$, worse with rest, relieved by exercise). Runs a progressive course completely independent of gut inflammation.
3. Ophthalmological:
   • Episcleritis: Mild, painless ocular hyperaemia without visual loss; parallels bowel flares.
   • Uveitis / Iritis: Severe ocular pain, visual blurring, profound photophobia, headache, and ciliary injection. Requires urgent slit-lamp examination (cells and flare in anterior chamber) and immediate topical/systemic corticosteroid therapy to avert permanent blindness.
4. Hepatobiliary:
   • Primary Sclerosing Cholangitis (PSC): Progressive fibro-obliterative destruction of intra- and extrahepatic bile ducts. Approximately $70-80\%$ of PSC patients have coexisting ulcerative colitis. Presents with fatigue, pruritus, jaundice, and a cholestatic biochemical profile (marked alkaline phosphatase and gamma-GT elevation). Diagnosis is confirmed by Magnetic Resonance Cholangiopancreatography (MRCP) demonstrating multifocal segmental strictures and bead-like ductal dilatations. Carries an elevated risk of cholangiocarcinoma and a 5-fold increased risk of colorectal cancer, mandating annual surveillance colonoscopy from the time of PSC diagnosis.

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Acute Severe Ulcerative Colitis (ASUC)

Acute severe ulcerative colitis (ASUC) is a medical emergency carrying significant mortality if recognized late. Patients require joint inpatient care under a gastroenterology and colorectal surgical team.

Truelove and Witts Criteria for Severity

Diagnosis requires $\ge 6$ bloody bowel motions per day PLUS at least one marker of systemic toxicity:

• Tachycardia: Heart rate $> 90\text{ beats/minute}$
• Fever: Oral temperature $> 37.8^\circ\text{C}$
• Anaemia: Haemoglobin $< 105\text{ g/L}$
• ASUC response: Truelove–Witts criteria assess bloody stool frequency with systemic disturbance at presentation. The Oxford day-3 rule uses stool frequency and CRP above 45 mg/L to predict failure of IV steroid treatment; it is not the admission definition.

Inpatient Diagnostic & Monitoring Protocol

1. Plain Abdominal Radiography: Essential on admission and with any clinical deterioration to exclude toxic megacolon (non-obstructive transverse colonic dilatation $> 5.5-6.0\text{ cm}$ with loss of haustration) and colonic perforation (subdiaphragmatic free gas).
2. Stool Microbiology: Urgent testing for Clostridioides difficile toxin (PCR / GDH) and enteric bacterial pathogens to exclude superimposed infectious colitis.
3. Flexible Sigmoidoscopy: Perform an unprepared, gentle examination with minimal air insufflation to assess mucosal severity and obtain mucosal biopsies to exclude Cytomegalovirus (CMV) colitis (indicated by intranuclear 'owl-eye' inclusion bodies).
4. Strict Avoidance of Motility-Altering Agents: Opiate analgesics, antidiarrhoeals (loperamide, diphenoxylate-atropine), and anticholinergic agents are strictly contraindicated because they induce colonic smooth muscle paralysis and precipitate toxic megacolon.
5. Venous Thromboembolism (VTE) Prophylaxis: Mandatory in all hospitalised patients with active IBD using subcutaneous low molecular weight heparin (LMWH). Active systemic inflammation induces a profound hypercoagulable state with a 3- to 4-fold elevation in deep venous thrombosis and pulmonary embolism risk; visible rectal bleeding is NOT a contraindication to prophylactic anticoagulation.

Primary references (checked 7 October 2026): Coeliac Australia oats guidance.