A 52 year-old male with HIV and diarrhea

A 52 year-old male with HIV presents with profuse, watery diarrhea of 5 days’ duration. A biopsy of the small intestine is shown here.

 

What is the most likely cause of this patient’s symptoms?

A. Cryptosporidium
B. Giardia
C. Acanthamoeba
D. Toxoplasma
E. Histoplasma

 

 

 

 

 

(Scroll down for the answer)

 

 

 

 

 

 

 

The causative organism in this case is cryptosporidium, a teeny tiny protozoan that is pretty hard to see until someone points it out to you for the first time. For that very reason, it frequently makes an appearance in pathology “unknown” conferences (where they give you a tray of slides, a little history (maybe), and them pimp you mercilessly for a diagnosis. The first year residents (or medical students) will often miss it since the organisms are miniscule and can be sparse. Once you’ve seen it, though, then you’ll remember to look for it the next time.

Cryptosporidium mainly affects children, in whom it causes either self-limited or persistent diarrhea. It also affects patients with AIDS, in whom it causes severe, chronic diarrhea. The organism is highly infectious, and is spread by fecal-oral transmission.

Diagnosis may be made on acid-fast examination of the stool, in which cryptosporidial oocysts are visible as round, red-staining structures. Histologic examination, which is usually not necessary for diagnosis, shows tiny round organisms projecting from the brush border, as seen in this image. Treatment involves antiparasitic therapy and nutritional support.

If you liked this case, and want to test yourself with other unknown cases, here are some to try:

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