A 32-year-old man is being evaluated due to several weeks of watery diarrhea. He has also had intermittent, crampy abdominal pain and has lost 7 kg (15.4 lb) during this period. The patient has a history of HIV and was hospitalized 6 months ago for Pneumocystis pneumonia. On physical examination, the patient is afebrile, and the abdomen is soft and nontender with no organomegaly. Stool tests for leukocytes and occult blood are negative. Endoscopy is performed, and mucosal biopsy shows an inflammatory infiltrate in the lamina propria and pathogens lining the epithelium, as shown in the exhibit.
The organisms have a cystic appearance on modified acid-fast staining. Which of the following is the most likely cause of this patient's condition?

Question

A 32-year-old man is being evaluated due to several weeks of watery diarrhea.  He has also had intermittent, crampy abdominal pain and has lost 7 kg (15.4 lb) during this period.  The patient has a history of HIV and was hospitalized 6 months ago for Pneumocystis pneumonia.  On physical examination, the patient is afebrile, and the abdomen is soft and nontender with no organomegaly.  Stool tests for leukocytes and occult blood are negative.  Endoscopy is performed, and mucosal biopsy shows an inflammatory infiltrate in the lamina propria and pathogens lining the epithelium, as shown in the exhibit.
  The organisms have a cystic appearance on modified acid-fast staining.  Which of the following is the most likely cause of this patient's condition?

Quizplus · Accepted Answer

11ec160b_37fb_c25b_9249_d3a52d804cf5_MD0001_00 Cryptosporidium is a protozoal organism that is a common cause of infectious diarrhea. Oocysts are ingested in contaminated food or water, travel to the small intestine, and shed sporozoites that attach to the epithelial cells. Individuals who are otherwise healthy often develop self-limited, watery (secretory) diarrhea. However, those with impaired cell-mediated immunity-particularly individuals with advanced AIDS (as is likely in this patient with HIV who recently had Pneumocystis pneumonia)-are at risk for life-threatening diarrhea with fluid loss of >20 L per day. Standard ova and parasite stool tests usually cannot detect the organism, and fecal leukocytes/occult blood tests are generally negative (because the pathogen does not cause inflammatory diarrhea). However, the diagnosis can often be made by modified acid-fast stain of the stool, which usually reveals oocysts. Histopathology generally shows villous blunting, an inflammatory infiltrate in the lamina propria, and basophilic Cryptosporidium organisms on the brush border of the mucosal surface. (Choice A) Clostridium difficile is a gram-positive, spore-forming bacterium that causes toxin-mediated inflammatory colitis (usually with fecal leukocytes/blood). It is not acid-fast or cystic. (Choice C) Entamoeba histolytica is an ameba that causes dysentery (bloody diarrhea). Histopathology generally reveals flask-shaped colonic ulcers with "foamy" trophozoites that resemble macrophages. (Choice D) Enteropathogenic Escherichia coli attaches to and effaces the small bowel epithelium, leading to watery, noninflammatory (no blood or leukocytes) diarrhea. However, this pathogen is a gram-negative rod, not an acid-fast cyst. (Choice E) Giardia lamblia is a protozoal organism that classically causes foul-smelling, greasy diarrhea and excessive flatulence after consumption of contaminated water. Stool microscopy generally shows oval/ellipsoid cysts or pear-shaped trophozoites; they are not acid-fast. (Choice F) Mycobacterium avium complex is a common opportunistic infection in patients with advanced AIDS (CD4 count <50/mm³) and often presents with diarrhea and weight loss. It is marked by acid-fast bacilli within macrophages. (Choice G) Salmonella enteritis is a common food-borne infection and usually presents with acute, self-limited diarrhea, vomiting, fever, and abdominal cramping. It is a gram-negative bacillus, not an acid-fast cyst. Educational objective: Cryptosporidium is a common cause of self-limited diarrhea in immunocompetent hosts, but may cause life-threatening diarrhea in immunocompromised patients (eg, advanced AIDS). Diagnosis may be made by visualizing oocysts with modified acid-fast stain in stool or basophilic organisms lining the brush-border in a biopsy.

A 32-Year-Old Man Is Being Evaluated Due to Several Weeks