Sunday, September 23, 2018

Answer to Case 512

Answer: Iodamoeba buetschlii

I thought this was a fun example of a relatively common parasite seen with an uncommon preparation. It's nice to see that an alternative stain such as Papanicoloau still allows for morphologic identification of the intestinal amebae.

The key morphologic features of this case are the small size of the organisms (primarily cysts, and possibly one trophozoite), nucleus with large karysome and lack of peripheral chromatin, and large cytoplasmic vacuole in the cytoplasm of the cyst form. As Florida Fan mentioned, the large glycogen-filled vacuole would be deeply stained with iodine if we had a wet mount preparation.

Some of you wanted to understand the basis for the Pap-stained anal/rectal smears, given that this is not something usually performed by the microbiology lab. The purpose is to exam for squamous cell dysplasia and carcinoma secondary to Human Papillomavirus infection - the same type of exam used for female cervical smears. Anal/rectal smears are usually done in the MSM population (men who have sex with men) - particularly when they engage in unprotected anal intercourse which puts them at risk for a variety of infections. Of course, when we exam smears from this source, we are bound to detect the occasional intestinal parasite as a incidental finding!

I published a similar case a few years back with some colleagues which you can read HERE.

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