Description

• A chronic, progressive inflammatory GI tract disorder, most commonly involving the terminal ileum (80%)
• Hallmark features of Crohn disease (CD)
  • Transmural inflammation that can result in fibrotic strictures, fistulas, fissures, or abscesses
  • Noncaseating granulomas (30%)
  • Skip lesions: diseased mucosa interspersed with normal mucosa; can be continuous, mimicking ulcerative colitis (UC)
  • Diverse presentations: ileitis (1/3), ileocolitis (1/3); isolated colitis (1/3)

Epidemiology

Incidence

• 3 to 20 cases per 100,000 person-years in North America; incidence rising globally
• Bimodal age distribution: Predominant age is 15 to 30 years, with a second smaller peak at 50 to 80 years.
• Women slightly more affected than men; increased incidence in northern climates
• Increased risk in whites versus nonwhites: 2- to 5-fold

Prevalence
247 cases per 100,000 persons

Etiology and Pathophysiology

• General: Clinical manifestations result from activation of inflammatory cells and subsequent tissue injury.
• Multifactorial: Genetics, environmental triggers, commensal microbial antigens, and immunologic abnormalities result in inflammation and tissue injury.

Genetics

• 15% of CD patients have a first-degree relative with inflammatory bowel disease (IBD); first-degree relative of an IBD patient has 3- to 30-fold increased risk of developing IBD by age 28 years.
• Associated genetic syndromes: Turner and Hermansky-Pudlak syndromes, glycogen storage disease type 1b

Risk Factors

Environmental factors

• Cigarette smoking doubles the risk of CD; tobacco cessation reduces flares and relapses.
• Dietary factors: higher incidence if diet high in refined sugars, animal fat or protein, processed or ultraprocessed foods

Commonly Associated Conditions

• Extraintestinal manifestations
  • Arthritis (20%): seronegative, small and large joints (ankylosing spondylitis [AS] or sacroiliitis [SI], associated with HLA-B27)
  • Skin disorders (10%): erythema nodosum, pyoderma gangrenosum, psoriasis
  • Ocular disease (5%): uveitis (associated with HLA-B27), iritis, episcleritis
  • Kidney stones: calcium oxalate stones (from steatorrhea and diarrhea) or uric acid stones (from dehydration and metabolic acidosis)
  • Osteopenia and osteoporosis; hypocalcemia
  • Hypercoagulability: venous thromboembolism prophylaxis essential in hospitalized patients
  • Gallstones: cholesterol stones resulting from impaired bile acid reabsorption
  • Primary sclerosing cholangitis (PSC) (5%)
• Conditions associated with increased disease activity
  • Peripheral arthropathy (not SI and AS)
  • Episcleritis (not uveitis)
  • Oral aphthous ulcers and erythema nodosum
• Complications: GI bleed, toxic megacolon, bowel obstruction, bowel perforation, peritonitis, malignancy, intra-abdominal fistula, perianal disease