USMLE RBCs in CSF

[usmleswot]

Hello everyone,

Got a question on USMLERx which I really didn't get.

Posting it below:

A 42 year old obtunded man is brought to the emergency department for evaluation and treatment. Results of a CT scan of the head prompt the performance of a lumbar puncture.

Opening pressure: 18mmH20
Lymphocytes: 100/mm3
RBCs: 500/mm3
Protein: 30mg/dL
Glucose: 50mg/dL

No xanthochromasia is notes and the results of a gram stain are negative. What class of drugs should be used as initial epiric treatment for this patient?

A. Antibiotics (Gm -ve coverage)
B. Antibiotics (Gm +ve coverage)
C. Antifungal agents
D. Antiretroviral agents
E. Antituberculous agents
F. Antiviral agents.

The Qbank seems to arbitrarily come to the decision that it's Herpes encephalitis. I didn't think there were pathognomonic findings for HSV encephalitis but apparently the presence of RBCs in CSF is specific for HSV?

Anyone know anything about this?

Thanks!

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[SBR249]

If it's an infectious process, then RBCs in the CSF is pretty specific for HSV encephalitis. At least on the step it is.

 

[usmleswot]

If it's an infectious process, then RBCs in the CSF is pretty specific for HSV encephalitis. At least on the step it is.

The question's pretty badly written, there's no denying that. I'd pretty much dismissed it when I read it, but it's the explanation that had me stumped. I've checked other sources and while the presence of RBCs in CSF has been associated with HSV, it's not something that's a consistent finding. Guess I'll just just take your word for the fact that it's a common association for the step. Thanks!

 

[SBR249]

It may not be a consistent finding in HSV encephalitis but I don't recall ever hearing it associated with another infectious process. So in that regard I'd say it's a pretty specific finding if not a sensitive finding. That and temporal lobe involvement would be what I would look for in HSV.

 

[usmleswot]

Cool. Thanks!