What is the most likely diagnosis and recommended management for a patient whose cerebrospinal fluid shows 2 white blood cells, protein 120 mg/dL, and glucose 60 mg/dL?

CSF Analysis: Likely Guillain-Barré Syndrome or Viral CNS Infection

This CSF profile—2 WBC/µL, protein 120 mg/dL, glucose 60 mg/dL—represents classic albuminocytologic dissociation most consistent with Guillain-Barré syndrome (GBS), though viral meningitis/encephalitis remains a critical differential that requires immediate exclusion with PCR testing. 1, 2, 3

Interpretation of the CSF Values

Why Bacterial Meningitis is Excluded

• Bacterial meningitis is essentially ruled out because the CSF protein of 120 mg/dL is well below the typical bacterial range (>220 mg/dL or >2.2 g/L), and protein <60 mg/dL (<0.6 g/L) makes bacterial disease very unlikely 1, 2
• The CSF glucose of 60 mg/dL is normal-to-elevated, whereas bacterial meningitis characteristically shows very low glucose with CSF:plasma glucose ratio <0.36 1
• The WBC count of 2 cells/µL is within normal limits (<5 cells/µL), and bacterial meningitis typically shows >100 cells/µL with neutrophil predominance 1, 4

Why Tuberculous and Fungal Meningitis are Unlikely

• TB meningitis characteristically shows markedly elevated protein (often >1 g/L) and very low glucose, neither of which is present here 1, 2
• Fungal meningitis typically presents with low CSF glucose and raised protein, inconsistent with this profile 1

The Two Most Likely Diagnoses

Guillain-Barré Syndrome (Primary Consideration)

• Albuminocytologic dissociation—elevated CSF protein with normal cell count—is the diagnostic hallmark of GBS 2, 3, 5
• This patient's protein of 120 mg/dL with WBC of 2/µL perfectly matches this pattern 3
• The diagnostic yield of elevated protein in GBS is 65-66% when using standard reference ranges, though this increases with longer duration from symptom onset to lumbar puncture 3
• Clinical correlation is essential: Look for progressive ascending weakness, areflexia, and sensory symptoms developing over days to weeks 2

Viral Meningitis/Encephalitis (Must Exclude Urgently)

• Viral CNS infections typically produce mildly elevated protein (tens to hundreds mg/dL) with normal or slightly low glucose, exactly matching this profile 1, 2, 4
• Critical caveat: 5-10% of HSV encephalitis cases have completely normal initial CSF findings, so normal cell count does not exclude viral infection 2, 4
• If the patient has headache with altered mental status, focal neurologic deficits, or unexplained vomiting, viral encephalitis becomes the primary concern and requires immediate empiric acyclovir 1, 2

Critical Missing Information That Changes Management

Simultaneous Plasma Glucose is Essential

• The CSF:plasma glucose ratio is far more informative than absolute CSF glucose alone 1, 2
• Normal ratio is >0.66; bacterial meningitis shows ratio <0.36 1
• Without plasma glucose, you cannot definitively interpret the CSF glucose of 60 mg/dL 1

CSF Cell Differential is Absolutely Required

• The CSF white cell count differential (neutrophils vs lymphocytes) is essential for diagnosis 1, 4
• Bacterial infections show neutrophil predominance, while viral infections show lymphocytic predominance 1
• This information was not provided but is critical for distinguishing between etiologies 1, 4

Immediate Diagnostic Workup Required

Send These CSF Tests Immediately

• CSF PCR for HSV-1, HSV-2, VZV, and enteroviruses to exclude viral CNS infection, which accounts for 90% of viral cases 2
• CSF cell count with differential to determine neutrophil vs lymphocyte predominance 1, 2
• CSF lactate: levels <35 mg/dL (or <2 mmol/L) effectively rule out bacterial disease with 93% sensitivity and 96% specificity 1, 2, 4
• CSF Gram stain and bacterial culture, though bacterial meningitis is already highly unlikely 1

Additional Testing Based on Clinical Context

• If progressive ascending weakness with areflexia: Arrange electrodiagnostic studies (nerve conduction studies and EMG) to confirm GBS 2
• If headache, altered mental status, or focal deficits: Start empiric acyclovir 10 mg/kg IV every 8 hours immediately while awaiting HSV PCR results 2
• Consider CSF oligoclonal bands and IgG index if autoimmune etiology is suspected 2

Clinical Context Determines Next Steps

If Clinical Picture Suggests GBS

• Look for progressive, symmetric ascending weakness developing over days to 4 weeks 2
• Examine for areflexia or hyporeflexia in affected limbs 2
• Assess respiratory function with serial vital capacity measurements, as 20-30% require mechanical ventilation 2
• The longer the duration from symptom onset to LP, the higher the diagnostic yield of elevated protein 3

If Clinical Picture Suggests Viral Encephalitis

• Start empiric acyclovir immediately if there is altered mental status, focal neurologic deficits, or persistent/progressive headache 1, 2
• Do not wait for PCR results to initiate treatment, as untreated HSV encephalitis has high mortality 2
• Obtain brain MRI with gadolinium to look for temporal lobe involvement characteristic of HSV encephalitis 2
• Remember: A second LP at 24-48 hours may show abnormalities if the first CSF is normal in early viral infection 4

Common Pitfalls to Avoid

Do Not Assume Normal WBC Excludes Infection

• 10% of bacterial meningitis patients have fewer than 100 cells/mm³, and some have normal cell counts, especially in early disease or immunocompromised patients 1, 4
• 5-10% of HSV encephalitis cases have completely normal initial CSF 2, 4

Do Not Overlook Age-Adjusted Reference Ranges

• Standard CSF protein upper limit of 45 mg/dL (0.45 g/L) may lead to overdiagnosis of abnormalities in older patients 5
• Age-adjusted reference ranges improve diagnostic specificity and reduce false positives 3, 5

Do Not Forget to Correct for Traumatic Tap

• If RBCs are present, subtract 1 WBC for every 700-7000 RBCs to determine true WBC count 4, 6
• Subtract 0.1 g/dL protein for every 100 RBCs present 4