Pathology

Crohn disease is characterized by segmental, transmural, granulomatous inflammatory changes that can occur anywhere along the gastrointestinal tract from the mouth to the perianal area. Disease of the terminal ileum is present in 80% of patients with Crohn disease, and 50% of patients have ileocolitis. Approximately 33% and 20% of patients demonstrate only ileal and colonic involvement, respectively. The finding of skip lesions between areas of normal bowel and cobblestoning of the intestinal mucosa is classic for Crohn disease. Chronic inflammation commonly leads to bowel stenosis.

Epidemiology

The yearly incidence of Crohn disease is between 3 and 14 cases per 100,000 people in North America, with a disease prevalence of 26 to 201 cases per 100,000. The incidence rate of Crohn disease has risen steadily, with the highest incidence found in North America and northern Europe. Crohn disease is more common in Caucasian and Latino people in the United States than in African Americans, Native Americans, and Asian Americans. Women have a 20% to 30% higher incidence than men do.

The cold chain hypothesis suggests that the rise in incidence of Crohn disease has been associated with the development of home refrigeration techniques. Bacteria that thrive in refrigerated foods, such as Yersinia and Listeria, are thought to play a role in stimulation of the immune and inflammatory responses that ultimately lead to Crohn disease.⁶ Exacerbations of Crohn disease may be worsened during periods of higher physiologic or mental stress.⁷ Other environmental factors such as cigarette smoking, use of nonsteroidal antiinflammatory drugs (NSAIDs), increased refined sugar intake, increased dietary fat, and decreased fiber intake have been linked to the development of Crohn disease.^8–11

Genetic mutations and chromosomal variants have also been linked to the development of Crohn disease. Specific alterations in the NOD2 gene are associated with a 20-fold increase in the likelihood of Crohn disease with ileal predilection.^12–15 Patients with Crohn disease may also be HLA-B27 positive.

Clinical Presentation

Patients with Crohn disease typically have abdominal pain, fever, diarrhea, and weight loss. Because Crohn disease involves the entire gastrointestinal tract, patients may suffer from oral ulcers, odynophagia, dysphagia, and symptoms of gastric outlet obstruction. Sinus tracts may develop and lead to common complications such as abscesses and fistula formation. Patients with Crohn disease can also have gastrointestinal bleeding, though to a lesser extent than patients with UC. Other complications include bowel obstruction, fissures, malignancy, malabsorption, malnutrition, and hypocalcemia.

Crohn disease is associated with an increased risk for demyelinating diseases, as well as a higher incidence of inflammatory processes such as asthma, arthritis, bronchitis, psoriasis, and pericarditis.^16,17 Approximately 20% of patients with Crohn disease experience one or more of the following extraintestinal manifestations of disease during their lifetimes: ankylosing spondylitis, uveitis, episcleritis, hepatitis, cholelithiasis, pancreatitis, primary sclerosing cholangitis, cholangiocarcinoma, nephrolithiasis, and erythema nodosum (Fig. 36.1; Box 36.1).

Fig. 36.1 Computed tomography scan showing terminal ileitis (arrow) in a patient with Crohn disease.

Pathology

UC is a recurring inflammatory disease confined to the mucosal layer of the colon and rectum only. Areas of inflammation are continuous, not segmental; patients commonly experience ascending disease from the rectum to the colon. Isolated rectal involvement is present in a minority of patients.