[29.1 ] A. This young man most likely has a viral meningitis given the modest CSF pleocytosis count with predominant lymphocytes. Given the high RBC count, it may be HSV. so acyclovir should be instituted until more specific testing can be done. However, because bacterial meningitis cannot be excluded based on the CSF analysis alone, empiric antibac-terials should be given until culture results are known, usually within 48 hours.
[29.2] D. Tuberculous meningitis is extremely difficult to diagnose, and the index of suspicion should be high in susceptible individuals. Certain clinical findings, such as nerve palsies, and CSF findings, such as an extremely low glucose and high protein levels with a fairly low WBC count, are highly suggestive but not diagnostic. Mortality is high and related to the delay in instituting therapy. The only definitive test is acid-fast bacillus (AFB) culture, but it can take 6-8 weeks to grow. PCR test for Mycobacterium tuberculosis is diagnostic if positive; however, the sensitivity is low, so a negative test does not rule out the disease. Findings such as a positive PPD. or CSF cell counts and protein levels that do not change with standard antimicrobial or antiviral therapies, can also suggest the diagnosis. Low CSF glucose is a hallmark of TB meningitis—if the glucose level falls at 48 hours, it is highly suggestive of TB. CT scan and MRI may demonstrate basilar meningitis in TB, but the finding is not specific.
[29.3] C. Listeria monocytogenes is a Gram-positive rod that causes approximately 10% of all cases of meningitis. It is more common in the elderly and in other patients with impaired cell-mediated immunity, such as patients on chemotherapy. It is also more common in neonates. It is not sensitive to cephalosporins, and specific therapy with ampicillin must be instituted if the suspicion for this disease is high.
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