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General Medicine · Infectious diseases: cryptococcal meningitis
Sample itemA 35-year-old man with HIV and a CD4 count of 40 cells/mm3 has had headache and low-grade fever for 3 weeks, with neck stiffness. Non-contrast CT is normal. CSF opening pressure is raised, and cell count shows few lymphocytes. Which CSF test has the highest sensitivity for the likely diagnosis?
Original practice item, not a recalled exam question. Nothing here is recorded.
The answer and the reasoning
C. Cryptococcal antigen by latex agglutination or lateral flow assay
Cryptococcal meningitis typically presents subacutely in advanced HIV, with few CSF inflammatory cells and a high opening pressure. CSF and serum cryptococcal antigen detection has a sensitivity of over 90%, higher than India ink microscopy which depends on the burden of organisms. Induction therapy is amphotericin B with flucytosine, and raised pressure is managed with repeated therapeutic lumbar punctures.
Option by option
A. CSF PCR for JC virus
JC virus causes progressive multifocal leukoencephalopathy, a white matter disease with normal pressure.
B. India ink staining
India ink is specific but misses cases with a low fungal load.
C. Cryptococcal antigen by latex agglutination or lateral flow assay (correct)
Antigen assays are the most sensitive rapid test.
D. CSF adenosine deaminase
Raised ADA supports tuberculous meningitis, which would show more cells and protein.
Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.
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