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Differentiating Features of Ulcerative Colitis and Crohn Disease
A classification of inflammatory bowel disease (IBD) based on scientific data has not gained acceptance. An early attempt was made to classify IBD according to two categories: (1) ulcerative colitis (UC) and Crohn disease; and (2) collagenous colitis, eosinophilic enteritis, Behçet disease, transient colitis, microscopic colitis, prestomal ileitis, pouchitis, and solitary rectal ulcer. None of these entities had a definitive etiology, resulting in overlap and confusion.
Most authorities group these IBD entities into UC, Crohn disease, and indeterminate colitis. However, IBD study still has no classification, with difficult clinical situations in which patients seem to have overlapping diseases, such as diverticulitis and Crohn disease. Nevertheless, because the etiology of each is unknown and because the most common disease entities are UC and Crohn disease, this chapter discusses the differentiating factors because these are important for clinical management and determining the course and prognosis of each. Many of the same therapeutic regimens are used for UC and Crohn disease, with subtle variations, and the clinician should understand the differences ( Fig. 94.1 ).
Differentiating Features of Ulcerative Colitis and Crohn Disease.
The differential diagnosis of UC and Crohn disease greatly overlaps, and for indeterminate colitis, a differentiation cannot be made. Furthermore, the IBD pattern appears to be changing with the changing environment and more information. The following differentiating features and comparisons, however, have held over the past few decades.
Presenting Symptoms
Patients with UC often have diarrhea that contains mucus or blood. At times, the patient may appear to have infectious gastroenteritis. However, the diarrhea persists even after therapeutic trials. Rarely, an extraintestinal manifestation, such as migratory joint pain, pyoderma gangrenosum, or acute toxic megacolon, may be the presenting symptom.
Patients with Crohn disease usually have abdominal pain and a change in bowel habits. They may have diarrhea. The presentation of Crohn colitis may be similar to that of UC. However, the diffuseness of Crohn disease may result in extracolonic symptoms in many patients. If Crohn disease has developed in the small bowel, symptoms of pain, fever, mass, or anemia may be present. If extracolonic symptoms include joint pain or liver disease, these may be the presenting symptoms.
Genetics and Heredity
UC and Crohn disease are complex genetic disorders with multiple contributing genes. Linkage studies implicated some unique genomic regions containing IBD susceptibility genes, with some unique to Crohn disease, some unique to UC, and some unique to both diseases. IBD II, on chromosome 12q, is observed more in UC. IBD I, on chromosome 16q, contains the Crohn disease-susceptible gene NOD2/CARD15. Patients of European descent show three major coding-region polymorphisms within NOD2/CARD15. One copy of the risk allele means the patient has a twofold to fourfold risk for Crohn disease, but with a double-dose carriage, the risk increases to 20-fold to 40-fold. Patients with ileal disease, earlier age of onset, and stricturing carry the NOD2/CARD15 allele. The genetic evaluation of these two diseases is constantly being studied and more detailed discussions are available in the references below.
Ethnic, racial, family, and twin studies reveal a leveling off in incidence and prevalence of UC and an increasing rate of Crohn disease. In addition, nonwhite persons appear to have a consistently lower rate of Crohn disease. The prevalence of Crohn disease per 100,000 population is 43.6 among white persons, 29.8 among black persons, 4.1 among Hispanic persons, and 5.6 among Asian persons. Furthermore, Jewish persons in the United States seem to be at greatest risk for twofold to fourfold higher incidence and twofold to ninefold higher prevalence. Family studies show IBD clusters within families, suggesting that genetics plays a major role. First-degree relatives have about a 10-fold to 15-fold increased risk. The risk overlaps; one family member may acquire Crohn disease and another, UC. In addition, asymptomatic family members appear to have an increased rate of positive serologic findings. Monozygotic twin concordance for Crohn disease is reported to be as high as 42% to 58%, a key factor supporting a major genetic influence.
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