A 42-year-old man with HIV comes to the emergency department with 3 days of abdominal pain, decreased appetite, and diarrhea. Temperature is 38 C (100.4 F), blood pressure is 98/60 mm Hg, and pulse is 110/min. Abdominal examination shows tenderness over the left lower quadrant without guarding or rebound tenderness. CD4 count is 38/mm³. Colonoscopy shows erythematous, friable mucosa with superficial ulcerations in the sigmoid and descending colon. Biopsy from the ulcers reveals inflammatory infiltrate, mucosal necrosis, and enlarged endothelial cells with large, ovoid nuclei containing prominent basophilic deposits. Which of the following is the most likely cause of this patient's gastrointestinal symptoms?

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11ec160b_381e_d9eb_9249_e1cd868983c3_MD0001_00 Cytomegalovirus (CMV) is the most common viral opportunistic infection of the gastrointestinal tract in patients with advanced AIDS. Initial infection with CMV is usually asymptomatic or similar to Epstein-Barr virus-induced mononucleosis. As with all members of the herpesvirus family, latent infection is established after resolution of the initial infection. Reactivation can occur at any time but is most common in the setting of immunosuppression. In patients with HIV, CMV colitis is the second most common reactivation syndrome after CMV retinitis. Patients with CMV colitis have fever, anorexia, weight loss, and abdominal pain. The pain may be vague initially but becomes more localized as the disease progresses. Colonoscopy shows mucosal erythema, erosions, and ulcerations. Histologic examination of biopsy specimens will reveal acute and chronic inflammatory changes, vasculitis, and large cells with large, ovoid nuclei containing centralized intranuclear basophilic inclusions (owl's eye appearance). (Choice A) Patients with advanced AIDS are at risk for disseminated Mycobacterium avium complex, which is often associated with diarrhea, abdominal pain, and weight loss. However, acid-fast staining organisms and necrotizing and non-necrotizing granulomas are typically seen on biopsy. (Choice B) Cryptosporidium is a protozoan parasite that causes watery diarrhea in both immunocompromised and immunocompetent patients. However, it primarily affects the small intestine, not the colon. Oocysts can be identified in the stool using microscopy with modified acid-fast stain; biopsy will show basophilic parasites attached to the mucosal brush border. (Choice C) Candida albicans is a normal part of human flora that often causes oropharyngeal and esophageal infections in patients with advanced AIDS. However, Candida and other yeasts (eg, Histoplasma capsulatum) are a rare cause of colitis. (Choice E) Clostridium difficile is an exotoxin-producing, anaerobic bacterium that can cause severe colitis, most commonly after antibiotic use. Patients usually have fever, abdominal pain, leukocytosis, and diarrhea. Endoscopy is not usually needed but often reveals mucosal pseudomembranes. Educational objective: Cytomegalovirus (CMV) is a common cause of colitis in patients with advanced AIDS. It is the second most common CMV reactivation disease in this population (CMV retinitis is the most common). Patients with CMV colitis often have abdominal pain, fever, diarrhea, and weight loss. Colonoscopy usually shows erythema, erosions, and ulcerations; colonic biopsy typically reveals large cells with prominent basophilic intranuclear inclusions.

A 42-Year-Old Man with HIV Comes to the Emergency Department