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28 September 2016 - Case of the Week #402

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Case of the Week #402

Clinical history:
A 46 year old man presented with untreated HIV since 2001, and multifocal high grade SIL in a background of anal warts. There was no diarrhea. He consistently refused antiretroviral treatment. Other findings are a recent severe outbreak of HSV2+, secondary syphilis (recently treated), eosinophilia secondary to Stronglyloides infection (recently treated) and CMV antibody positive. His CD4 count was 56. An anal smear was obtained.

Micro images:

What is your diagnosis?

Iodamoeba buetschlii

The anal Pap smear shows many amebic cysts between 5-20 microns in size, with a prominent clear space in the cytoplasm. They have a single nucleus with a large central karyosome, and a small space between the karyosome and nuclear membrane. This is morphologically consistent with Iodamoeba butschlii. The name Iodamoeba comes from the large clear space in the cytoplasm, which is a glycogen mass that stains red-brown on iodine stain.

I. butschlii is an uncommon, non-pathogenic ameba that can colonize the large intestine. It is acquired by ingesting contaminated food or water. It has been reported as a fecal contaminant in anal Paps (Diagn Cytopathol 2014;42:775) and cervical Paps (Cytopathology 2010;21:342).

There does not appear to be an association between I. butschlii and HIV infection. In one study, it was more common in stool specimens from men who have sex with men (Diagn Cytopathol 2014;42:775).

Other amebae that resemble I. butschlii include Entamoeba histolytica and Endolimax nana. E. histolytica has a similar size, but its cytoplasm often contains ingested red blood cells, and its nucleus has a smaller karyosome with a peripheral rim of condensed chromatin. Differentiating I. butschlii from E. nana and other non-pathogenic amebae may be difficult and requires a stool examination in the microbiology lab (Diagn Cytopathol 2014;42:775).

Non-pathogenic ameba can travel with pathogenic organisms, such as Giardia, Cryptococcus and pathogenic ameba. In this case, stool studies showed no other pathogenic organisms.

Discussion by: Dr. Hillary Z. Kimbrell, Myriad Genetics, Inc., Utah (USA)

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