Chapter 3. Inflammatory Bowel Disease: Medical Considerations

• Crohn disease and ulcerative colitis are chronic inflammatory diseases with well-described epidemiologic and clinical features.
• Genetic factors, immune dysregulation, and microbial gut flora all influence disease susceptibility.
• No single symptom, physical finding, or test result can diagnose inflammatory bowel disease (IBD); the diagnosis is a clinical one based on consistent findings obtained from the history, physical examination, and laboratory, endoscopic, histologic, and radiologic studies.
• Multiple conditions can mimic IBD; infectious pathogens are a particular concern.
• Intestinal complications commonly occur in IBD, many of which are predictable on the basis of disease type, location, severity, or duration; extraintestinal complications also occur, typically in association with active disease.
• Patients with long-standing colitis are at increased risk of developing colorectal cancer (CRC) and should be evaluated for dysplastic changes predictive of subsequent or synchronous malignancy.
• 5-Aminosalicylates, steroids, antibiotics, and immunomodulators have been mainstays of therapy; the choice of appropriate medication is based on multiple variables, including disease type, location, and severity.
• Biologic medications offer multiple powerful therapeutic options; the optimal time to apply these medications remains to be clarified.

The inflammatory bowel diseases, Crohn disease and ulcerative colitis, are chronic inflammatory illnesses of the gastrointestinal tract. Although significant advancements have been made in our understanding of the pathogenesis of these conditions, their ultimate cause remains idiopathic. The immunologic basis of IBD is discussed in Chapter 2. This chapter addresses the diagnosis and medical treatment of IBD. Surgical considerations are discussed in detail in Chapter 4.

Epidemiology

Crohn disease and ulcerative colitis have low incidences of new diagnosis; however, as a chronic condition typically diagnosed in the young, IBD has a relatively high prevalence. Estimates of incidence and prevalence vary among studies, with significant geographic and socioeconomic variations. The incidence of ulcerative colitis in North America is estimated to be 8–15 per 100,000 persons, with a prevalence of 170–230 per 100,000. Crohn disease has an estimated incidence of 5–15 per 100,000 and prevalence of 140–200 per 100,000. An increased incidence and prevalence of both forms of IBD is found in developed nations, northern locale (at least within the northern hemisphere), and urban environments; among Caucasians; and among persons of Jewish ethnicity. In industrialized countries, the incidence of Crohn disease has risen significantly over the past half century, whereas that of ulcerative colitis has remained relatively steady. In developing countries, the incidence of both forms of IBD has dramatically risen.

IBD typically presents at a relatively young age, often in adolescence. The median age of diagnosis for Crohn disease and ulcerative colitis is the third and fourth decades of life, respectively. Studies have suggested a second, smaller peak in incidence of IBD in the sixth and seventh decades, although this association is clearer for ulcerative colitis than for Crohn disease.

Etiology