Tuberculous Meningitis
The most likely diagnosis is B. Tubercular meningitis, based on the classic triad of month-long prodromal fever, lymphocytic-predominant CSF pleocytosis with markedly elevated protein (3.6 g/L, >10x normal), and low CSF glucose (2.7 mmol/L, below normal range despite normal serum glucose) 1.
Diagnostic Reasoning
The clinical presentation is pathognomonic for tuberculous meningitis (TBM):
- Subacute course: One month of fever followed by 5 days of headache and 2 days of altered sensorium represents the classic staged progression of TBM
- CSF profile:
- Turbid appearance with 240 cells/μL
- Lymphocytic predominance (73%) - this is the key distinguishing feature
- Markedly elevated protein (3.6 g/L) - typically >1 g/L in TBM, yours is 10-16x normal
- Low CSF glucose (2.7 mmol/L) - below the normal range of 2.50-3.89 mmol/L, with CSF:serum glucose ratio of approximately 0.37 (normal >0.5)
- Nuchal rigidity confirms meningeal involvement
Why Not the Other Options?
Viral meningoencephalitis (D) would show:
- Normal or mildly elevated protein (<1 g/L)
- Normal CSF glucose - this is the critical differentiator
- More acute presentation (days, not weeks)
Pyogenic meningitis (C) would demonstrate:
- Neutrophil predominance (>80%), not lymphocytic
- More acute presentation (hours to 1-2 days)
- Much lower CSF glucose (<1.5 mmol/L typically)
Septicemia (A) doesn't explain the specific CSF findings or meningeal signs
Important Caveats
While TBM classically shows lymphocytic predominance, early TBM can present with neutrophil predominance that converts to lymphocytic over days to weeks 2. Your patient's 23% neutrophils with 73% lymphocytes indicates he's past the early neutrophilic phase, consistent with his month-long illness.
Immediate Management Priorities
Based on ATS/CDC/IDSA guidelines 1:
Initiate four-drug therapy immediately without waiting for culture confirmation:
- Isoniazid (INH)
- Rifampin (RIF)
- Pyrazinamide (PZA)
- Ethambutol (EMB)
Duration: 2 months of four-drug therapy, then continue INH + RIF for additional 7-10 months (total 9-12 months) 1.
Add dexamethasone - adjunctive corticosteroids are recommended for all TBM patients, with greatest mortality benefit in Stage II disease (lethargic/drowsy patients like yours, where mortality decreased from 40% to 15% with dexamethasone) 1.