Case #178 – April, 2006

A 29-year-old man went to a local health clinic with complaints of intermittent diarrhea for a few months. He did not report any other symptoms but said he had difficulty sleeping sometimes. A stool specimen was collected and preserved in both 10% formalin and polyvinyl-alcohol (PVA). An ova and parasite (O & P) examination was performed. Figure A shows what was seen on a concentrated wet mount preparation, and Figure B shows what was seen on a wet mount stained with iodine. Figures C and D show what was seen on a trichrome stained smear made from the PVA preserved specimen. Objects measured 7 to 10 µm in diameter. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

The organisms shown in the images are cyst-like forms of Blastocystis hominis. Diagnostic features were:

the size of the organisms, which was within the range for B. hominis (normally 8 to 10 micrometers in diameter, but can be 5 to 30 micrometers).
the presence of small nuclei within the peripheral ring of cytoplasm. In trichrome stained preparations, these nuclei often appear red.
the presence of a large, centrally located vacuole or central body. In trichrome stained preparations, these bodies appear green to dark purple in color.