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PE27.2 | Tuberculous Meningitis — SDL Guide (Part 3)
Self-Assessment
The scenarios below require you to apply the staging, diagnostic, and treatment frameworks from this module in an integrated way. Work through the reasoning before reading the answers — the goal is to rehearse the clinical thinking process, not just fact retrieval.
Scenario: A 3-year-old boy is brought with a 2-week history of fever, irritability, and headache. Over the past 4 days he has been increasingly drowsy and has had 2 generalised seizures. Examination: febrile 38.2°C, drowsy (GCS 11/15), neck stiffness, right CN VI palsy, no papilloedema. His BCG scar is present. Mantoux = 8 mm. CSF: appearance clear with cobweb clot on standing; cells 200/mm³ (85% lymphocytes); protein 350 mg/dL; glucose 18 mg/dL (serum 72 mg/dL).
Q1: What is the MRC stage of TBM in this child, and what is the prognostic implication?
Q2: Does a Mantoux of 8 mm exclude TBM in this child?
Q3: What is the ATT regimen and total treatment duration?
Q4: What drug interaction must you consider if you use phenytoin for his seizures?
Answers:
1. Stage II (drowsy + CN VI palsy + focal deficit). Stage II prognosis: good chance of full recovery with early treatment, but risk of permanent deficit if delayed.
2. No. Mantoux may be negative in 30–50% of TBM cases due to immunosuppression from severe disease. The cobweb clot, lymphocytic pleocytosis, very high protein, and low glucose are more diagnostically useful than the Mantoux.
3. Intensive phase: 2 months HRZE; continuation phase: 10 months HR; total 12 months. Add dexamethasone (0.4 mg/kg/day) tapered over 4–6 weeks.
4. Phenytoin and carbamazepine are CYP450 enzyme inducers that significantly lower plasma levels of rifampicin and isoniazid. Prefer levetiracetam for seizure control in TBM patients on ATT.
SELF-CHECK
Which of the following CSF findings is MOST characteristic of tuberculous meningitis and distinguishes it from bacterial meningitis?
A. WBC 5,000/mm³ with 90% neutrophils
B. WBC 200/mm³ with 85% lymphocytes, protein 300 mg/dL, cobweb clot
C. WBC 50/mm³ with 80% lymphocytes, protein 60 mg/dL, normal glucose
D. WBC 800/mm³ with 70% neutrophils, normal glucose
Reveal Answer
Answer: B. WBC 200/mm³ with 85% lymphocytes, protein 300 mg/dL, cobweb clot
The TBM CSF profile is: lymphocytic pleocytosis (typically 100–500 cells, >80% lymphocytes), markedly elevated protein (often >100 mg/dL and sometimes >500 mg/dL), low glucose, and — pathognomonic when present — a cobweb clot on standing. Option A is bacterial meningitis (neutrophilic). Option C resembles viral meningitis (lymphocytic but low protein and normal glucose). Option D has a mixed/predominantly neutrophilic picture. The combination of very high protein, lymphocytic pleocytosis, low glucose, and cobweb clot is highly characteristic of TBM.