Which CSF pattern is most consistent with viral meningitis/encephalitis?

• A. Lymphocytic pleocytosis with normal glucose and mildly elevated protein
• B. Neutrophilic pleocytosis with low glucose
• C. High opening pressure with low protein
• D. Elevated glucose with eosinophilic pleocytosis

Answer: (A)

Viral meningitis/encephalitis most commonly presents with lymphocytic pleocytosis, normal CSF glucose, and only mildly elevated protein. This pattern reflects a predominately lymphocytic inflammatory response in the meninges, and glucose remains largely normal because viruses and inflammatory cells do not drive the same glucose consumption that bacteria do. The protein is elevated due to increased permeability of the blood-brain barrier, but not to the extent seen in bacterial meningitis.

In contrast, bacterial meningitis typically shows a neutrophilic predominance with low CSF glucose and markedly elevated protein, reflecting rapid bacterial metabolism and intense inflammatory response. Patterns with high opening pressure but low protein, or elevated glucose with eosinophilic pleocytosis, do not fit the typical viral picture and point toward other etiologies such as non-viral meningitis or parasitic/fungal processes.