Tubercular Meningitis is the Most Likely Diagnosis
Based on the clinical presentation of subacute onset (month-long fever), lymphocytic predominance in CSF (73%), low CSF glucose (2.7 mmol/L, below normal 2.50-3.89), and markedly elevated protein (3.6 g/L, normal 0.22-0.33), this patient most likely has tubercular meningitis.
Key Diagnostic Features Supporting TB Meningitis
CSF Profile Analysis
The cerebrospinal fluid findings are classic for tubercular meningitis 1:
- Lymphocytic predominance (73%) with total cell count of 240/µL falls within the typical range of 5-500 cells/µL seen in TB meningitis 1
- Markedly elevated protein (3.6 g/L) is characteristic of tuberculous meningitis, which shows significantly elevated protein levels 1
- Low CSF glucose (2.7 mmol/L) with CSF/blood glucose ratio of approximately 0.37 (2.7/7.22) is consistent with TB meningitis, which typically shows ratios <0.5 2, 1
- Turbid appearance reflects the inflammatory process with elevated cell count 3
Clinical Presentation
The temporal pattern strongly favors TB meningitis 1:
- Prolonged fever for one month before neurological symptoms is characteristic of the subacute course of tuberculous meningitis
- Progressive symptoms with headaches for 5 days followed by altered sensorium for 2 days
- Nuchal rigidity indicating meningeal inflammation
Why Other Diagnoses Are Less Likely
Viral Meningoencephalitis (Option D)
While viral infections can cause lymphocytic pleocytosis, several features argue against this diagnosis 1:
- CSF glucose is typically normal or only slightly low in viral meningitis (ratio >0.36), not markedly decreased as in this case 2, 1
- Protein elevation is mild in viral meningitis, not the marked elevation (3.6 g/L) seen here 1
- Clinical course is typically acute, not the month-long prodrome of fever 4
Bacterial (Pyogenic) Meningitis (Option C)
The CSF profile does not support typical bacterial meningitis 3, 1:
- Neutrophil predominance expected in acute bacterial meningitis, but this patient has only 23% neutrophils with 73% lymphocytes 5
- While lymphocytic predominance can occur in bacterial meningitis with low cell counts (<1,000/mm³), it accounts for only 32% of such cases and is uncommon 5
- Partially treated bacterial meningitis could show lymphocytic predominance, but no antibiotic history is mentioned 1
Septicemia (Option A)
This is not a CNS diagnosis and does not explain the CSF findings 4.
Critical Diagnostic Considerations
CSF Glucose Ratio Interpretation
The CSF/blood glucose ratio of 0.37 falls in an intermediate zone 2:
- Ratio <0.23 predicts bacterial meningitis with 99% certainty 2
- Ratio >0.36 suggests viral etiology 2
- Ratio 0.23-0.36 requires additional evaluation, particularly for TB meningitis when combined with very low absolute CSF glucose (<2.2 mmol/L has 68% sensitivity and 96% specificity for TB) 2
Lymphocytic Pleocytosis Differential
The American Academy of Neurology notes that monocyte/lymphocyte predominance occurs in 1:
- Viral meningitis (most common, but CSF glucose typically normal)
- Tuberculous meningitis (with very low glucose and high protein)
- Fungal meningitis (in immunocompromised patients)
- Partially treated bacterial meningitis
Recommended Next Steps
Immediate management should include empiric anti-tuberculous therapy while awaiting confirmatory testing 1:
- CSF PCR for tuberculosis and acid-fast bacilli staining/culture 1
- Chest imaging to identify pulmonary TB
- HIV testing given the association with TB meningitis
- Consider CSF lactate (>35 mg/dL would suggest bacterial over TB etiology) 1
- Neuroimaging to assess for complications such as hydrocephalus or tuberculomas 4
Common Pitfall to Avoid
Do not delay anti-tuberculous treatment while awaiting culture confirmation, as TB meningitis has high morbidity and mortality if treatment is delayed, and cultures may take weeks to become positive 1.