A 20-year-old man presents with several days of diarrhea with a small amount of rectal bleeding with each bowel movement. This is his second episode of bloody diarrhea; the first seemed to resolve after several days and occurred several weeks ago. He has cramps that occur with each bowel movement, but feels fine between bouts of diarrhea. He has no travel history outside of the United States. He is of Jewish descent and has a cousin with Crohn disease. Colonoscopy shows mucosal friability with superficial ulceration and exudates confined to the rectosigmoid colon, and he is diagnosed with ulcerative colitis (Figure 67-1).
Ulcerative colitis in the rectosigmoid colon as viewed through the colonoscope. (Reproduced with permission from Marvin Derezin, MD.)
Inflammatory bowel disease (IBD) comprises ulcerative colitis (UC) and Crohn disease (CD). The intestinal inflammation in UC is usually confined to the mucosa and affects the rectum with or without parts or the entire colon (pancolitis) in an uninterrupted pattern. In CD, inflammation is often transmural and affects primarily the ileum and colon, often discontinuously. CD, however, can affect the entire GI tract from mouth to anus.
Incidence of UC in the West is 8 to 14 per 100,000 people and 6 to 15 per 100,000 people for CD.1 Prevalence for UC and CD in North America (one of the highest rates in the world) is 37.5 to 248.6 per 100,000 people and 16.7 to 318.5 per 100,000 people, respectively; IBD therefore affects an estimated 1.3 million people in the United States.2 Rates of IBD are increasing both in the West and in developing countries.1
Age of onset is 30 to 40 years for UC and 20 to 30 years for CD. A bimodal distribution with a second peak at ages 60 to 70 years has been reported but not confirmed.1 Pediatric patients account for up to 20% of cases.
Predilection for those of Jewish ancestry (especially Ashkenazi Jews) followed in order by non-Jewish whites and African Americans, Hispanics, and Asians.1
Inheritance (polygenic) plays a role with a concordance of 38% to 58% for CD and 6% to 18% for UC in monozygous twins and a risk of about 10% in first-degree relatives of an incidence IBD case.2
ETIOLOGY AND PATHOPHYSIOLOGY
Unknown etiology—Current theory is that colitis is an inappropriate response to microbial gut flora or a lack of regulation of intestinal immune cells in a genetically susceptible host with failure of the normal suppression of the immune response and tissue repair.2,3
Genetic regions containing nucleotide oligomerization domain 2 (NOD2; encodes an intracellular sensor of peptidoglycan), autophagy genes (regulate clearing of intracellular components like organelles), and components of ...