A 52 year-old male presents with abdominal pain and bloody diarrhea which had a gradual onset over the last 3 weeks. He has lost 8 pounds during this period of time. A cecal biopsy is performed, and a representative section is shown here at two magnifications.

What is the most likely diagnosis?

A. Cryptosporidiosis
B. Amoebiasis
C. Giardiasis
D. Ascariasis
E. Candidiasis

(Scroll down for the answer)

The diagnosis in this case is amebiasis. The most common agent of amebic enterocolitis is Entamoeba histolytica, an tiny parasite spread through ingestion of cysts in contaminated food or water. The trophozoite forms are round, and if you look closely, you can often see intracytoplasmic red cells, as seen in the higher power image above.

The organisms frequently invade through the mucosa and into the submucosa, often with lateral extension, as seen in this image. Lesions like this are sometimes called “flask-shaped ulcers.” Occasionally, the nasty little thing invade other organs, such as the liver, lung, and heart. Most patients can be treated on an outpatient basis, unless there is severe colitis or extraintestinal disease.

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