What cerebral spinal fluid (CSF) analysis results are consistent with a diagnosis of both meningitis and encephalitis, characterized by hyperproteinemia, turbid appearance, hypoglycorrhachia, low pressure on initial puncture, and leukocytosis?

CSF Findings in Meningitis and Encephalitis

In both meningitis and encephalitis, the CSF analysis typically shows high protein levels, cloudy appearance, low glucose levels, and increased white blood cells, but NOT low pressure on initial puncture. 1, 2

Characteristic CSF Findings in Meningitis and Encephalitis

Opening Pressure

• Typically elevated in both bacterial meningitis and viral encephalitis (200-500 mm H₂O) 1
• Low pressure on initial puncture is NOT consistent with meningitis or encephalitis

Appearance

• Cloudy/turbid appearance is typical, especially in bacterial meningitis 1
• Clear appearance is more common in viral meningitis, but can be cloudy in some viral encephalitis cases 1, 2

White Blood Cell Count

• Increased WBC (pleocytosis) is present in both conditions 1, 2
  • Bacterial meningitis: Typically >100 cells/μL, predominantly neutrophils
  • Viral encephalitis: Typically 5-1000 cells/μL, predominantly lymphocytes
  • HSV encephalitis: Usually tens to hundreds of cells/μL 1

Protein Levels

• Elevated protein is present in both conditions 1, 2
  • Bacterial meningitis: Markedly elevated (>0.6 g/L)
  • Viral meningitis/encephalitis: Mildly to moderately elevated
  • Tuberculous meningitis: Markedly elevated

Glucose Levels

• Low glucose (hypoglycorrhachia) is characteristic of bacterial meningitis and some cases of encephalitis 1, 2
  • CSF:plasma glucose ratio <0.36 has 93% sensitivity and specificity for bacterial meningitis 1
  • Viral encephalitis: Normal to slightly low glucose
  • HSV encephalitis: Usually normal CSF:plasma glucose ratio 1

Differential Diagnosis Based on CSF Findings

Parameter	Bacterial Meningitis	Viral Encephalitis	Tuberculous Meningitis	Fungal Meningitis
Opening Pressure	Raised	Normal/mildly raised	Raised	Raised
Appearance	Turbid, cloudy	Clear (can be cloudy)	Clear or cloudy	Clear or cloudy
WBC (cells/μL)	>100	5-1000	5-500	5-500
Cell type	Neutrophils	Lymphocytes	Lymphocytes	Lymphocytes
Protein (g/L)	Raised	Mildly raised	Markedly raised	Raised
Glucose	Very low	Normal/slightly low	Very low	Low
CSF:plasma glucose	<0.36	Normal/slightly low	Very low	Low

Important Clinical Considerations

• In approximately 5-10% of adults with HSV encephalitis, initial CSF findings may be normal with no pleocytosis and a negative HSV PCR 1
• If the first CSF is normal in patients with suspected HSV encephalitis, a second CSF examination 24-48 hours later is recommended 1, 2
• CSF lactate <2 mmol/L can help rule out bacterial disease 1, 2
• The CSF/blood glucose ratio is a precise indicator for bacterial meningitis (optimal cut-off=0.36, sensitivity=92.9%, specificity=92.9%) 3
• In cases of traumatic lumbar puncture, the white cell count can be corrected by subtracting 1 leukocyte for every 7000 erythrocytes/mm³ in the CSF 1, 2

Diagnostic Approach

1. Obtain CSF via lumbar puncture (after CT if clinically indicated)
2. Measure opening pressure (should be elevated in meningitis/encephalitis)
3. Assess appearance (cloudy suggests infection)
4. Analyze cell count and differential
5. Measure protein and glucose levels (compare glucose to simultaneous plasma glucose)
6. Perform Gram stain and culture
7. Order PCR testing for viral pathogens (HSV, VZV, enteroviruses)

Remember that low pressure on initial puncture is NOT consistent with meningitis or encephalitis, which typically present with normal to elevated opening pressures.