Wednesday, December 15, 2010
1:26 AM | Posted by Shams Burki | Edit Post
A. Broad-based, budding yeasts
B. Budding yeasts in a "pilot's wheel" arrangement
C. Cylindrical arthroconidia
D. Encapsulated budding yeasts
E. Filamentous molds
F. Septate hyphae with microconidia and macroconidia
The correct answer is D. This clinical vignette has some nice info for USMLE, LEARN everything about HIV/AIDS. This is a classic case of Cryptococcus neoformans meningitis. Clues included the patient population (HIV positive), geographic area (Mississippi and Missouri river beds), and diagnostic form (encapsulated yeast). Cryptococcus is a monomorphic fungus, unlike many of the classic pathogens within the fungal group, so the encapsulated yeast form would be found both in clinical specimens and in the environment as the infectious form.
Broad-based, budding yeasts (choice A) would be the forms expected to be found in clinical specimens (not environmental forms) from patients infected with Blastomyces dermatitidis, which is far more likely to present with skin and bone lesions than with meningitis.
Budding yeasts in a "pilot's wheel" arrangement (choice B) would be the form expected to be found in clinical specimens (not environmental forms) from patients infected with Paracoccidioides brasiliensis, which is limited in geographic region to Central and South America and typically presents as a primary pulmonary disease.
Cylindrical arthroconidia (choice C) would be the transmission forms characteristic of Coccidioides immitis, which may be a cause of fungal meningitis in immunologically compromised individuals, but is geographically restricted to the sub-Sonoran desert zone of the U.S. (San Joaquin valley fever).
Filamentous molds (choice E) are the transmission forms of several of the fungal agents (eg, Coccidioides, Blastomyces, Paracoccidioides) but Cryptococcus does not have a filamentous form.
Septate hyphae with microconidia and macroconidia (choice F) are the transmission (environmental) forms of Histoplasma capsulatum, which is not an encapsulated yeast in spite of its name. It is primarily a pulmonary infection acquired by exposure to the droppings of birds or bats.