Which is true of encephalitis CSF findings?

• A. Gram stain positive with neutrophilic pleocytosis
• B. WBC predominantly neutrophils with low protein
• C. Mononuclear WBC predominant; protein >100; CRP normal; glucose normal to slightly decreased
• D. Gram stain negative; high CRP

Answer: (C)

In encephalitis, the CSF pattern is most consistent with a viral process. The key finding is a predominance of mononuclear (lymphocytic) white cells, rather than neutrophils, along with elevated protein and typically normal or only mildly decreased glucose. C-reactive protein in the CSF is usually not elevated in viral infections. Gram stain is typically negative because there are no bacteria in the CSF.

So the statement describing mononuclear WBC predominance with protein elevation (>100 mg/dL), CRP normal, and glucose normal to slightly decreased best fits viral encephalitis. By contrast, bacterial meningitis tends to show neutrophilic pleocytosis, low glucose, high protein, and often a positive Gram stain with elevated CRP.