chronic, relapsing inflammatory disease of all the layers intestinal wall (transmural) and can occur from mouth to anus. Characterized by skip lesions.

<aside> 💡 any part of GIT but commonest caecum and terminal ileus (70%).

• patchy
• thick and narrow
• transmural, deep
• chronic granulomas </aside>

Demographics

• increased in developed countries, whites, Jews, females
• any age, common <20-40yrs, minor peak >60yrs

Aetiology

• 30% Genetic susceptibility
  • 15% family history, 30-59% concordance in twins.
  • HLA antigens DR7 - 27%
• Environmental Factors
  • Hygiene hypothesis
  • Western diet
  • smoking
• Immune dysfunction → Autoimmunity

Risk factors

• Smoking strong risk factor
• Family Hx
• genetic predisposition (e.g., mutation of the NOD2 gene, HLA-B27 association)