Inflammatory bowel disease - Crohn's vs ulcerative colitis - features, treatment

1. Definition and clinical relevance

Inflammatory bowel disease (IBD) describes chronic, relapsing and remitting, non-infectious inflammation of the gastrointestinal tract. The two principal entities are Crohn's disease (CD) and ulcerative colitis (UC).

Epidemiology:

• Commonly affects young people, typically presenting between 15 and 40 years of age
• Both sexes affected roughly equally
• Clear familial tendency

Pathogenesis:

• Cause not precisely understood
• Thought to arise from environmental trigger acting on genetically susceptible individual

Pattern of inflammation in ulcerative colitis:

• Inflammation limited to colorectal mucosa
• Extends proximally in continuous fashion from rectum
• Proctitis: disease confined to rectum
• Pancolitis: disease extends to involve entire colon

Pattern of inflammation in Crohn's disease:

• Any part of gut from mouth to anus can be affected
• Characteristically shows skip lesions (normal bowel between inflamed segments)
• Common sites: ileocaecal region, ileum, colon (often patchy or segmental), stomach, duodenum, oesophagus, mouth and lips (orofacial disease)
• Perianal disease and proctitis particularly associated with CD

Why it matters:

• Significant morbidity through diarrhoea, malnutrition, growth failure in children, extra-intestinal complications
• Increased long-term risk of colorectal cancer (CRC)
• Need for structured colonoscopic surveillance

2. Key values, thresholds and decision rules

Distinguishing Crohn's disease from ulcerative colitis

Colorectal cancer surveillance in IBD

Faecal calprotectin as a decision tool

Faecal calprotectin is useful in distinguishing IBD from irritable bowel syndrome (IBS) and helps rule out IBD in patients presenting with bowel symptoms. A negative faecal immunochemical test (iFOBT) can help rule out significant bowel disease including colorectal cancer.

Red flag for surgical emergency

Toxic megacolon (colonic dilatation on plain imaging or CT) is a surgical emergency and must be recognised urgently.

3. Approach: presentation and differential

History

The hallmark of both CD and UC is diarrhoea with blood and slimy mucus. Enquire specifically about:

• Duration, frequency and nocturnal symptoms (chronic, relapsing-remitting course over more than 6 months suggests organic disease).
• Presence of blood and mucus in the stool.
• Abdominal pain, urgency and tenesmus.
• Weight loss, fatigue, and in children reduced growth velocity.
• Features of malabsorption: steatorrhoea, symptoms of vitamin deficiency (for example megaloblastic anaemia from B12 malabsorption in ileal CD).
• Perianal symptoms (pain, discharge, fistulae) which point toward Crohn's.
• Extra-intestinal symptoms: joint, skin, eye and hepatobiliary symptoms.
• Family history of IBD and colorectal cancer.
• Medication history, since many drugs provoke altered bowel habit (metformin, opiates causing constipation with overflow, laxatives, antiemetics such as metoclopramide, and weight-loss agents such as orlistat or acarbose); antibiotics and enteral feeding are common causes of non-infective diarrhoea.

Examination

• General: weight, nutritional status, pallor of anaemia, signs of dehydration.
• Abdomen: tenderness, distension, palpable mass (an inflammatory ileocaecal mass in CD).
• Perianal examination: fissures (which in CD are often multiple and indolent), haemorrhoids, skin tags, perianal abscess or fistula, proctitis.
• Orofacial inspection for mouth and lip involvement in CD.
• Extra-intestinal manifestations: skin, joints and eyes.

Differential

• Irritable bowel syndrome (IBS): a chronic (>6 months) relapsing-remitting condition with abdominal pain relieved by defecation or associated with altered bowel frequency/stool form, plus features such as altered stool passage and bloating; diagnosis is clinical with no confirmatory test and normal investigations.
• Infective diarrhoea / colitis (including Clostridioides difficile, which may require fidaxomicin or faecal microbiota transplant in severe or chronic disease).
• Drug-induced diarrhoea (as above).
• Ileocolonic tuberculosis, which can mimic Crohn's and is common in low and middle income countries such as India; microscopy and culture for TB of available tissue is essential where relevant.
• Colorectal cancer, particularly with alarm features.

4. Investigations

Bedside

• Stool testing: microscopy and culture to exclude infection (including TB culture where relevant), and C. difficile testing.
• Faecal calprotectin: useful to distinguish IBD from IBS and to help rule out IBD in symptomatic patients.
• Faecal immunochemical test (iFOBT): a negative result helps rule out significant bowel disease including colorectal cancer.

Bloods

• Full blood count for anaemia (including megaloblastic anaemia from B12/folate malabsorption in ileal disease).
• Inflammatory markers.
• Nutritional markers and evidence of malabsorption.
• Albumin (relevant both to nutritional status and to drug protein-binding considerations).

Imaging and endoscopy

• Colonoscopy is central to diagnosis, extent assessment, and biopsy; it is also the modality for dysplasia and CRC surveillance in IBD and is associated with reduced risk of colon cancer and mortality in this group.
• CT with intraluminal and intravenous contrast enhances diagnostic capability and can demonstrate bowel wall thickening and complications; note the significant radiation dose (approximately 10 millisieverts).
• Ultrasound can show dilated, fluid-filled loops in obstruction and bowel wall thickening, and can assess inflammatory conditions and guide biopsy or percutaneous drainage.
• Plain imaging or CT to detect toxic megacolon.
• CT colonography may be used as an alternative where colonoscopy is incomplete or the lumen is obstructed.

5. Management

Management is directed by disease type, extent, severity and complications, in consultation with gastroenterology. The following steps are grounded in the retrieved material.

Step 1: Confirm the diagnosis and exclude mimics. Treat any identifiable cause (infection, drug side effect, constipation) and review. Refer to gastroenterology if treatment fails, if atypical symptoms appear, or when organic disease is suspected. Referral should be urgent (to be seen within 2 weeks) for concerning presentations, and inflammatory bowel disease should be actively considered in patients under 40 years with suggestive symptoms.

Step 2: Medical therapy. Both conditions are managed with agents that induce and maintain remission. From the grounding:

• 5-aminosalicylates (sulfasalazine and mesalamines) are used and are considered safe in pregnancy.
• Corticosteroids for acute flares.
• Thiopurines as immunomodulators.
• Biologic agents, for example infliximab (a typical regimen is 5 mg/kg at weeks 0, 2 and 6, then every 8 weeks, with the option to increase to 10 mg/kg), used for both CD and UC. Biologics require appropriate baseline testing and carry serious toxicity risks that must be monitored.

Corticosteroids and locally injected or oral corticosteroids, together with NSAIDs, are also used for associated inflammatory arthritis.

Step 3: Nutritional support. Address malnutrition and micronutrient deficiencies. In children, monitor growth velocity. Dietary approaches (including enteral nutrition strategies) have a role in Crohn's disease.

Step 4: Surgery. Surgery is recommended for complications, especially in Crohn's disease. Options include:

• Ileostomy, for which UC, CD, familial polyposis coli and obstruction are recognised indications.
• Colostomy, indicated in CD among other conditions.
• Strictureplasty in CD, preferred over resection when much small bowel has already been resected and strictures are short with intervening normal mucosa, to preserve functional bowel length.
• Emergency surgery for toxic megacolon.

Step 5: Manage obstruction when it arises. Focus on symptom improvement and decompression (for example a large-bore nasogastric tube), attention to hydration and nutrition (including intravenous fluid), and prokinetics such as metoclopramide in partial obstruction to encourage bowel function.

Step 6: Cancer surveillance. Enrol appropriate patients in colonoscopic surveillance as above; this is associated with reduced colon cancer incidence and mortality in IBD.

6. Australian-specific considerations

• Colorectal cancer surveillance in IBD is guided by Cancer Council Australia clinical practice guidelines. Commence surveillance from the onset of IBD symptoms; those with isolated proctitis or small bowel Crohn's disease do not require surveillance colonoscopy. Start earlier and survey more intensively in patients with primary sclerosing cholangitis, family history of CRC, diagnosis before age 40, or stenosing colonic Crohn's.
• Faecal calprotectin is embedded in Australian practice to separate IBD from IBS and to triage referral, consistent with international guidance.
• Referral pathways: general practitioners should refer to gastroenterology when there is failure of first-line management, atypical or alarm features, or suspected organic disease, with urgency (seen within 2 weeks) for high-concern presentations. This aligns with primary care red-flag pathways.

Clinical pearls

• CD affects any part of the gut from mouth to anus with skip lesions and transmural involvement; UC is confined to the colorectal mucosa in a continuous pattern from the rectum proximally. Getting this distinction right drives every subsequent management decision.
• Perianal disease (multiple indolent fissures, skin tags, fistulae, perianal abscess) strongly points toward Crohn's disease and should be looked for on every examination of a patient with chronic diarrhoea.
• Faecal calprotectin is the key non-invasive tool to distinguish IBD from IBS; a negative iFOBT also helps exclude significant colorectal pathology including cancer.
• Toxic megacolon detected on plain imaging or CT is a surgical emergency; recognise it early and escalate immediately.
• Colonoscopic surveillance for colorectal cancer is indicated from the onset of IBD symptoms except in isolated proctitis and small bowel Crohn's disease; higher-risk groups (primary sclerosing cholangitis, family history of CRC, diagnosis before age 40, stenosing colonic Crohn's) need earlier and more frequent surveillance.
• Strictureplasty is preferred over resection in short Crohn's strictures when significant small bowel has already been removed, preserving functional bowel length.
• Infliximab 5 mg/kg at weeks 0, 2 and 6 then every 8 weeks (increasing to 10 mg/kg if needed) is a recognised biologic regimen for both CD and UC; appropriate baseline testing and ongoing monitoring for serious toxicity are mandatory before and during therapy.
• In children with IBD, always assess growth velocity; failure to grow is a critical red flag that may indicate undertreated disease requiring escalation beyond routine adult management thresholds.