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PE27.3 | Meningitis Differentiation — Summary & Reflection
KEY TAKEAWAYS
Meningitis Differentiation — Key Points
| Feature | Bacterial | Viral | TBM |
|---|---|---|---|
| Tempo | Acute (hours–days) | Acute (hours–days) | Subacute (weeks) |
| Appearance | Turbid/purulent | Clear | Clear ± cobweb clot |
| WBC | >1,000 (up to 10,000) | 50–500 | 100–500 |
| Cell type | Neutrophils >80% | Lymphocytes >80% | Lymphocytes >80% |
| Protein | ↑↑ >100 mg/dL | Mildly ↑ 50–100 mg/dL | ↑↑↑ often >300 mg/dL |
| Glucose | ↓↓ ratio <0.40 | NORMAL ratio >0.60 | ↓↓ ratio <0.40 |
| Gram stain | Positive 60–80% | Negative | Negative |
| Best rapid test | Blood culture/Gram stain | Clinical + PCR | GeneXpert on CSF |
Five-step method: Appearance → Cell count/differential → Protein → Glucose ratio → Special tests → Synthesis with clinical context.
Key discriminators: Neutrophils = bacterial; Normal glucose = viral (not TBM); Cobweb clot + very high protein + low glucose = TBM.
Pitfalls: Partially treated bacterial → mixed cells, borderline glucose; Early TBM → neutrophilic shift; Traumatic LP → artefactual WBC elevation.
REFLECT
Think about this: You have just interpreted a CSF report that shows lymphocytic pleocytosis, low glucose, and very high protein in a 5-year-old with 2 weeks of subacute fever. The GeneXpert on CSF is negative (sensitivity 60–70%). Should you start ATT? What framework do you use to make this decision when the confirmatory test is negative? Reflect on the concept of treating the most dangerous diagnosis that cannot be excluded, and consider what information from the history and examination would raise or lower your threshold to start ATT empirically in this child.