CSF Patterns in Suspected Meningitis

Core Principle

• Interpret cerebrospinal fluid (CSF) findings as a physiologic pattern, not as a single laboratory value.
• Record and interpret:
  • Opening pressure
  • Fluid appearance
  • Leukocyte count and differential
  • Protein
  • CSF glucose with a paired serum glucose value
  • Microbiology
  • Lactate
• Integrate the CSF profile with illness timing, host factors, examination findings, and clinical severity.

Bacterial Meningitis

• Typical CSF pattern:
  • Elevated opening pressure
  • Turbid or purulent fluid
  • Neutrophilic pleocytosis, often greater than 1,000 cells per microliter
  • Protein greater than 100 mg/dL
  • Low CSF glucose or a CSF-to-serum glucose ratio below 0.4
  • Elevated lactate
• Gram stain is often positive, but a negative result does not neutralize a dangerous clinical syndrome.
• Do not delay treatment when bacterial meningitis is clinically suspected.

Viral Meningitis

• Typical CSF pattern:
  • Clear fluid
  • Normal or mildly elevated opening pressure
  • Lymphocytic pleocytosis
  • Mildly elevated protein
  • Normal glucose
  • Normal lactate
• Clinical pearl:
  • Early viral disease may be neutrophil-predominant before the expected lymphocytic pattern develops.
  • A single CSF snapshot is less reliable than serial clinical reasoning and pathogen-directed testing.

Tuberculous and Fungal Meningitis

• Shared CSF features may include:
  • Lymphocytic pleocytosis
  • Low glucose
  • Elevated protein
  • Elevated lactate
• Tuberculous meningitis may produce very high opening pressure and protein concentrations, sometimes greater than 1,000 mg/dL.
• A negative tuberculosis polymerase chain reaction result does not exclude tuberculous meningitis because sensitivity is limited.
• Fungal evaluation may include culture and cryptococcal antigen testing.
• A very high opening pressure with a positive cryptococcal antigen result supports cryptococcal meningitis.

Special Findings

• CSF eosinophilia shifts the differential toward:
  • Parasitic infection
  • Coccidioidomycosis
  • Drug reaction
• When red cells contaminate CSF, use a rough correction of 1 white blood cell per 250 to 500 red blood cells rather than overcalling pleocytosis.

Empiric Therapy and Practical Takeaways

• The provided local source lists ceftriaxone, vancomycin, and ampicillin as empiric therapy for suspected adult central nervous system infection.
• Ampicillin provides Listeria coverage in immunocompromised or other risk groups.
• Steroid use is scenario-specific, particularly when pneumococcal or tuberculous meningitis is suspected.
• Follow local protocols for empiric treatment and adjunctive therapy.

Summary Takeaway

• Use the full CSF pattern and the clinical context to distinguish bacterial, viral, tuberculous, fungal, and other causes of meningitis.
• Do not let a negative Gram stain, an early neutrophilic pattern, or a negative tuberculosis polymerase chain reaction result override a high-risk clinical syndrome.
• Treat suspected bacterial meningitis promptly while diagnostic testing proceeds.

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Confirm treatment decisions against current local protocols.