Answer to Case 639

Answer to Case of the Week 639: Microsporidia spores. As many of you noted, the differential diagnosis includesToxoplasma gondiitachyzoites. Here are some of the key morphologic features:Location in the cornea. [T. gondiiis usually found in the posterior chamber of the eye (e.g., retina)]Small oval shape with well-defined contours on H&E:Unfortunately,T. gondiitachyzoites are much less defined on H&E - they can be very difficult to see. They often don ' t even have a nice crescent shape like we seen on Giemsa-stained air-dried impression smears. They often just look like little blobs in tissue.Strong Gram-positivity on tissue Gram stain. (In comparison,T. gondiitachyzoites do not stain well, and may appear Gram-negative).Other considerations would include small fungi such as Candida glabrata. Therefore, a panel of histochemical stains may also be useful. Microsporidia spores may be focally GMS positive, but aren ' t usually uniformly positive like yeasts are. Also, microsporidia spores will stain focally positive with an acid fast stain, strongly positive with warthin-starry stain, and have a polar dot-like positivity with PAS. They are also often birefringent with polarized light.If you still wanted to do additional studies to confirm your diagnosis, I would recommend immunohistochemistry and PCR forT. gondii, and transmission electron microscopy. Microsporidia spores are beautifully detailed on TEM. This is still a conventional method for microsp...
Source: Creepy Dreadful Wonderful Parasites - Category: Parasitology Source Type: blogs