Answer to Case 594

Answer to Parasite Case of the Week 594: Entamoeba coli cysts and trophozoite.

This case shows all of the classic features of Entamoeba coli, with large organisms and, most importantly, cysts that contain more than 4 nuclei. According to the CDC DPDx, "karyosomes may be compact or diffuse and are usually eccentrically located. Peripheral chromatin is present and is often coarse, granular, and irregularly arranged along the nuclear membrane but may be more uniform. The cytoplasm of mature cysts may contain diffuse glycogen. Chromatoid bodies are seen less frequently than in E. histolytica. When present, they are usually splinter like with pointed ends, whereas the chromatoid bodies of E. histolytica have rounded ends. The cytoplasm [of trophozoites] is usually coarsely granular and vacuolated (often described as “dirty” cytoplasm). Pseudopodia may be seen and are often short and blunt."

While I would hesitate to make the diagnosis on any one of these features alone, together they strongly support the diagnosis of E. coli. Again, the presence of >4 nuclei in the cyst is the strongest diagnostic feature.

Thanks again to Florida Fan for donating this classic case!