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); rectal sparing; 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 is rising globally. Bimodal age distribution: Predominant age is 15 to 30 years, with a second smaller peak at 50 to 80 years. Women are slightly more affected than men; increased incidence in northern climates

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 the age of 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 is 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