What is the most likely diagnosis for a patient with meningitis symptoms, hypoglycorrhachia, and lymphocytic predominance in cerebrospinal fluid (CSF) analysis?

Tuberculous Meningitis

The most likely diagnosis is B. Tuberculous meningitis, based on the critical finding of a CSF/plasma glucose ratio <0.4 combined with lymphocytic predominance. 1

Key Diagnostic Reasoning

The CSF/plasma glucose ratio is the decisive factor here. **When the CSF/plasma glucose ratio is <0.5, tuberculous meningitis is highly likely, and this patient's ratio of <0.4 strongly points to TB meningitis rather than viral or aseptic meningitis.** 1 The Centers for Disease Control emphasizes that viral meningitis maintains a CSF/plasma glucose ratio >0.36, which clearly excludes viral meningitis in this case. 1

Why Not the Other Options?

Viral meningitis (Option A) is excluded because:

• Viral meningitis typically presents with normal or only slightly low CSF glucose 1
• The CSF/plasma glucose ratio remains >0.36 in viral meningitis 1
• This patient's ratio of <0.4 falls below the viral meningitis threshold 1

Bacterial meningitis (Option C) is unlikely because:

• Bacterial meningitis typically shows neutrophil predominance (80-95%), not lymphocytic predominance 1
• While bacterial meningitis can have low CSF glucose, the lymphocytic predominance argues strongly against acute bacterial infection 1
• Lymphocytic predominance in bacterial meningitis occurs in only 14 of 103 cases (13.6%) and is most common when CSF WBC is <1,000/mm³ 2

Aseptic meningitis (Option D) is a non-specific term referring to meningitis with sterile bacterial culture and lymphocytic predominance, but does not explain the profound hypoglycorrhachia. 3 TB meningitis is a specific form of aseptic meningitis that accounts for the low glucose. 4

Supporting Features of TB Meningitis

The combination of lymphocytic predominance with profound hypoglycorrhachia is characteristic of tuberculous meningitis. 1, 5 Additional supporting features typically include:

• Markedly elevated CSF protein (typically >1 g/L) 1
• CSF WBC count 5-500 cells/μL 1, 6
• Subacute presentation over days to weeks 1, 5

Critical Clinical Pitfall

The absolute CSF glucose value can be misleading when serum glucose is abnormal—always calculate the CSF/plasma glucose ratio. 1 The European Society of Clinical Microbiology emphasizes that the ratio is more diagnostically useful than absolute values. 1 In this case, even though the CSF glucose appears "normal" at 250, the ratio to blood glucose reveals the true hypoglycorrhachia.

Important Caveat

While partially treated bacterial meningitis can present with lymphocytic predominance after 48-72 hours of antibiotics 7, the profound hypoglycorrhachia (CSF/plasma ratio <0.4) and the clinical context make TB meningitis the most likely diagnosis. 1 If there is any history of antibiotic use, this should be factored into the clinical assessment, but the CSF/plasma glucose ratio remains the strongest discriminator. 1