MEDizzy - A 39-year-old man presents with bloody diarrhea. Multiple

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Gastrointestinal System

A 39-year-old man presents with bloody diarrhea. Multiple stool examinations fail to reveal any ova or parasites. A barium examination of the patient’s colon reveals a characteristic “string sign.” A colonoscopy reveals the rectum and sigmoid portions of the colon to be unremarkable. A biopsy from the terminal ileum reveals numerous acute and chronic inflammatory cells within the lamina propria. Worsening of the patient’s symptoms results in emergency resection of the distal small intestines. Gross examination of this resected bowel reveals deep, long mucosal fissures extending deep into the muscle wall. Several transmural fistulas are also found. Which of the following is the most likely diagnosis?

ExplanationThe two inflammatory bowel diseases (IBDs), Crohn disease (CD) and ulcerative colitis (UC), are both chronic, relapsing inflammatory disorders of unknown etiology. They both may show very similar morphologic features and associations, such as mucosal inflammation, malignant transformation, and extragastrointestinal manifestations that include erythema nodosum (especially ulcerative colitis), arthritis, uveitis, pericholangitis (especially with ulcerative colitis, in which sclerosing pericholangitis may produce obstructive jaundice), and ankylosing spondylitis. CD is classically described as being a granulomatous disease, but granulomas are present in only 25% to 75% of cases. Therefore, the absence of granulomas does not rule out the diagnosis of CD. CD may involve any portion of the gastrointestinal tract and is characterized by focal (segmental) involvement with “skip lesions.” Involvement of the intestines by CD is typically transmural inflammation, which leads to the formation of fistulas and sinuses. The deep inflammation produces deep longitudinal, serpiginous ulcers, which impart a “cobblestone” appearance to the mucosal surface of the colon. Additionally in Crohn disease, the mesenteric fat wraps around the bowel surface, producing what is called “creeping fat,” and the thickened wall narrows the lumen, producing a characteristic “string sign” on x-ray. This narrowing of the colon, which may produce intestinal obstruction, is grossly described as a “lead pipe” or “garden hose” colon. In contrast to CD, UC affects only the colon, and the disease involvement is continuous. The rectum is involved in all cases, and the inflammation extends proximally. Because UC involves the mucosa and submucosa, but not the wall, fistula formation and wall thickening are absent (but toxic megacolon may occur). Grossly, the mucosa displays diffuse hyperemia with numerous superficial ulcerations. The regenerating, nonulcerated mucosa appears as “pseudopolyps.”