Enumerate the csf findings in tuberculous meningitis
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Finding Sources
Finding Sources
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I now have comprehensive, well-sourced CSF data from multiple authoritative textbooks. Here is the full answer:
CSF Findings in Tuberculous Meningitis
1. Opening Pressure
- Elevated - increased intracranial pressure is typical, reflecting impaired CSF absorption and developing hydrocephalus.
2. Appearance
- Clear or slightly turbid (xanthochromic or opalescent in some cases). Unlike bacterial meningitis, it rarely looks frankly purulent.
- A "cobweb clot" (delicate fibrin web) may form on standing - a classic but non-specific sign.
3. Cell Count (Pleocytosis)
- Typically 50-500 white cells/mm³ (rarely exceeds 500).
- Early disease: mixed polymorphonuclear and lymphocytic cells.
- After several days: lymphocytic predominance in the majority of cases.
- Note: a persistent polymorphonuclear pleocytosis can occasionally occur with TB (also seen with Nocardia, Aspergillus, Actinomyces).
4. Protein
- Always elevated - typically 100-200 mg/dL in most cases.
- Can be markedly higher (>500 mg/dL) if CSF flow is blocked at the spinal cord level (spinal block).
5. Glucose (Hypoglycorrhachia)
- Reduced to below 40 mg/dL in most cases.
- Falls gradually - may only become clearly low several days after admission (unlike pyogenic meningitis where it drops sharply early).
- CSF-to-serum glucose ratio < 0.5 is characteristic.
- Rarely falls to the very low levels seen in conventional bacterial meningitis.
6. Chloride
- Reduced CSF chloride - historically a recognized feature, secondary to the low glucose and altered composition (less commonly measured today).
7. Microbiology
| Test | Finding | Comments |
|---|---|---|
| Acid-fast bacilli (AFB) smear / Ziehl-Neelsen stain | Positive in 10-50% | Sensitivity highly variable; large volume (up to 10 mL) and repeat LPs improve yield |
| Culture (Lowenstein-Jensen / BACTEC) | Gold standard | Slow: takes 3-4 weeks; rapid culture techniques can shorten to <1 week |
| PCR (nucleic acid amplification) | Sensitivity ~80%, ~10% false-positive rate | Rapid; multiplex PCR targeting multiple TB genes has better sensitivity than single-primer PCR |
| Dot-ELISA (antigen/antibody detection) | Positive in ~86% of suspected TBM | Only ~5% positivity in pyogenic meningitis |
8. Special/Ancillary CSF Tests
- Adenosine deaminase (ADA): Significantly elevated in TBM compared to other meningitides; useful as a rule-in test at high levels. (Note: also elevated in some bacterial meningitides.)
- Interferon-gamma release assay (IGRA) on CSF: Highly sensitive, ~90% specific for active TB infection; useful adjunct.
- Fibrin web / pellicle formation: Classic feature when CSF is allowed to stand at room temperature.
9. Electrolytes
- Hyponatremia is common systemically (and reflected in CSF sodium) - due to SIADH or adrenal insufficiency from adrenal tuberculosis.
Quick Comparison Summary
| Parameter | Typical TBM Finding |
|---|---|
| Pressure | Elevated |
| Appearance | Clear/turbid, cobweb clot |
| WBC | 50-500/mm³, lymphocytic predominance |
| Protein | 100-200 mg/dL (elevated) |
| Glucose | <40 mg/dL (CSF:serum ratio <0.5) |
| AFB smear | Positive in 10-50% |
| Culture | Positive (weeks) |
| PCR | ~80% sensitive |
| ADA | Elevated |
Sources:
- Adams and Victor's Principles of Neurology, 12th Ed., pp. 728-729
- Henry's Clinical Diagnosis and Management by Laboratory Methods
- Tintinalli's Emergency Medicine: A Comprehensive Study
- Rosen's Emergency Medicine
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