A 53-year-old man was referred with a 7-day history of diffuse abdominal pain and watery diarrhea. He had been diagnosed as having schizophrenia two years previously and had been treated in a long-term-care hospital. He had not traveled to the tropics in recent years. On examination, his abdomen was distended and had signs of peritonitis. A fecal occult blood test result was positive. Sigmoidoscopy demonstrated erythematous mucosa with numerous raised, whitish-yellow plaques throughout the rectosigmoid colon, an appearance that suggested pseudo-membranous colitis (A). After sigmoidoscopy, a chest film showed subdiaphragmatic intraperitoneal air. Exploratory laparotomy was performed urgently, and a cecal perforation with a gangrenous appendix was found. The appendix and cecum were resected and an ileostomy created. Histo-logic examination of the resected colon demonstrated tro-phozoites of Entamoeba histolytica in the appendiceal wall (B, H&E, orig. mag. x400). Stool examinations for Clostridium difficile toxin and culture were negative. The patient was treated with antibiotics including metroni-dazole for 14 days, and he recovered without further difficulty.
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