MBChB Year 2: Inflammatory Bowel Disease

Inflammatory Bowel Disease (IBD)

• IBD is a chronic condition characterized by inappropriate immune responses to normal gut flora.
• It includes two main disorders:
  • Ulcerative colitis (UC), which is confined to the colon and rectum, affecting mucosa and submucosa.
  • Crohn disease (CD), known for regional enteritis that can impact any part of the gastrointestinal tract, exhibiting transmural involvement.

Epidemiology

• Predominantly observed in developed countries, consistent with the hygiene hypothesis.
• Presents in adolescence and early twenties.

Pathogenesis

• IBD is idiopathic, resulting from:

  • Host interaction defects with gastrointestinal flora.
  • Intestinal epithelial barrier dysfunction.
  • Aberrant mucosal immune responses leading to increased permeability.

• Transepithelial microbial flux triggers immune responses, creating a self-amplifying cycle resulting in IBD.

• Genetic factors include higher disease risk in affected families and a 50% concordance in monozygotic twins for CD.

Genetics and Immune Responses

• NOD2 polymorphisms linked to CD; regulates immune response to luminal microbes.
• Other genes like ATG16L1 and IRGM are involved in microbial recognition.
• CD is associated with polarized TH1 responses, while UC shows TH2 responses.
• IL-23 receptor polymorphisms may provide protection in CD, whereas IL-10 gene polymorphisms are linked to UC.

Epithelial Defects and Microbiota

• Barrier dysfunction due to tight junction defects and transporter gene alterations.
• Microbiota composition influences immune responses; altering gut flora can aid in managing IBD.

Crohn Disease Morphology

• Can appear in any gastrointestinal tract area; most common in the ileum, ileocecal valve, and cecum.
• Typically presents with skip lesions and granular serosa, thickened rubbery bowel wall, and stricture formation.

Gross Features of CD

• Aphthous ulcers and cobblestone appearance due to interspersed mucosa elevation.
• Fistula tracts and granulomas may develop, with granulomas possible in mesenteric lymph nodes.

Clinical Features of CD

• Intermittent attacks include diarrhea, fever, and abdominal pain, with asymptomatic periods lasting weeks or months.
• Extensive CD can lead to malnutrition, iron deficiency, B12 deficiency, and protein-losing enteropathy.
• Surgical resection often needed for complications like fibrotic strictures or fistulas, with recurrence seen in 40% at anastomoses.
• Extraintestinal manifestations may include uveitis, sacroiliitis, and an increased risk of colonic cancer.

Ulcerative Colitis Morphology

• UC affects the colon in a continuous manner from the rectum upward; skip lesions are absent.
• Involves mucosal inflammation with potential backwash ileitis.

Gross Features of UC

• Characterized by reddened, granular mucosa with inflammatory pseudopolyps and extensive ulcers.
• Mucosal damage can lead to toxic megacolon and perforation.

Microscopic Features of UC

• Mucosal inflammation primarily affects the mucosa and submucosa; features include crypt abscesses and glandular distortion.
• Granulomas, skipped lesions, and fissures not present.

Clinical Features of UC

• Patients experience intermittent bloody mucoid diarrhea and abdominal pain with relapses common.
• Extraintestinal manifestations include joint pain, uveitis, and skin lesions; increased risk of colon cancer persists.

Indeterminate Colitis

• 10% of IBD patients cannot be definitively classified between UC and CD.

Colitis Associated Neoplasia

• Risk of malignancy rises 8 to 10 years after onset of IBD, greater in extensive disease.
• Patients require regular surveillance with biopsies for early detection of neoplasia.

This quiz covers Inflammatory Bowel Disease (IBD), focusing on its chronic nature and the immune responses involved. It includes details on the two primary disorders associated with IBD, making it essential for students of the GIT and hepatobiliary system. Test your understanding of this important medical topic.