How can meningitis be viral with low CSF glucose?

Low CSF Glucose in Viral Meningitis

Low CSF glucose can occur in viral meningitis, particularly in the early stages of infection, and does not rule out a viral etiology. 1

CSF Characteristics in Meningitis

Bacterial vs. Viral Meningitis

• While low CSF glucose is classically associated with bacterial meningitis, it can also occur in certain viral meningitis cases, especially early in the disease course 1
• The CSF/blood glucose ratio is considered the most precise indicator for bacterial meningitis (optimal cut-off=0.36, sensitivity=92.9%, specificity=92.9%) 2
• In viral meningitis due to specific pathogens like mumps, lymphocytic choriomeningitis virus (LCM), and herpes simplex, CSF glucose levels lower than 50% of blood glucose are not uncommon 1

Early CSF Findings in Viral Meningitis

• Early in viral meningitis, especially with enteroviral infections, the CSF frequently contains a predominance of polymorphonuclear leukocytes and may even have a low glucose level 1
• A shift from polymorphonuclear leukocytes to mononuclear cells within 12 hours makes viral meningitis the likely diagnosis 1
• No single CSF test is fully reliable in distinguishing bacterial meningitis from other forms of meningitis, and results should be interpreted in the clinical context 3

Diagnostic Considerations

CSF Parameters

• The CSF leukocyte count is considered the best diagnostic parameter for differentiating bacterial meningitis from other diagnoses 3
• CSF lactate determination has been shown to be the most sensitive and efficient test to distinguish bacterial from aseptic meningitis on admission 4
• Multiple diagnostic algorithms have been developed to help differentiate between bacterial and viral meningitis, but none are 100% sensitive 5

Point-of-Care Testing

• Bedside glucose testing of CSF fluid using glucometers shows good correlation with laboratory measurements and can help with rapid decision-making 6, 7
• The optimal cut-off of the CSF/blood glucose ratio calculated from a bedside glucometer was found to be 0.46, with a sensitivity of 94.1% and specificity of 91% for bacterial meningitis 7

Clinical Implications

Management Decisions

• If bacterial meningitis is suspected and lumbar puncture is delayed for any reason, empirical antibiotic therapy should be started immediately after blood cultures are obtained 3
• In patients with suspected viral meningitis who initially have polymorphonuclear predominance in CSF, antibiotics may be withheld if a repeat spinal tap within 12 hours shows a shift to mononuclear cells 1

Special Considerations

• Prior antibiotic treatment may modify CSF findings, though CSF WBC count may not be greatly affected by antibiotics given before lumbar puncture 3
• In immunocompromised patients, normal CSF parameters do not rule out meningitis 3

Clinical Pearl

• The identification of a specific viral agent in body fluids, especially the CSF, in a patient with aseptic meningitis is important as it can shorten hospital stay and eliminate unnecessary antimicrobial therapy 1