Chapter 26: Inflammatory Bowel Disease

INTRODUCTION

• There are two forms of idopathic inflammatory bowel disease (IBD): ulcerative colitis (UC), a mucosal inflammatory condition confined to the rectum and colon, and Crohn’s disease, a transmural inflammation of gastrointestinal (GI) mucosa that may occur in any part of the GI tract. The etiologies of both conditions are unknown, but they may have a common pathogenic mechanism.

ETIOLOGY AND PATHOPHYSIOLOGY

• Factors involved in cause of IBD include infectious agents, genetics, the environment, and the immune system. There is thought to be shift toward the presence of more proinflammatory bacteria in the GI tract, often referred to as dysbiosis. Several genetic markers and loci have been identified that occur more frequently in patients with IBD. The inflammatory response with IBD may indicate abnormal regulation of the normal immune response or an autoimmune reaction to self-antigens.

• Th1 cytokine activity is excessive in CD and increased expression of interferon-γ in the intestinal mucosa and production of IL-12 are features of the immune response in CD. In contrast, Th2 cytokine activity is excessive with UC (with excess production of IL-13). Tumor necrosis factor-α (TNF-α) is a pivotal pro-inflammatory cytokine that is increased in the mucosa and intestinal lumen of patients with CD and UC.

• Antineutrophil cytoplasmic antibodies are found in a high percentage of patients with UC and less frequently with CD.

• Smoking appears to be protective for ulcerative colitis but associated with increased frequency of Crohn disease. The use of nonsteroidal anti-inflammatory drugs (NSAIDs) may trigger disease occurrence or lead to disease flares.

• UC and Crohn disease differ in two general respects: anatomical sites and depth of involvement within the bowel wall. There is, however, overlap between the two conditions, with a small fraction of patients showing features of both diseases (Table 26–1).

ULCERATIVE COLITIS

• UC is confined to the colon and rectum and affects primarily the mucosa and the submucosa. The primary lesion occurs in the crypts of the mucosa (crypts of Lieberkühn) in the form of a crypt abscess.

• Local complications (involving the colon) occur in the majority of patients with UC. Relatively minor complications include hemorrhoids, anal fissures, ...