CNS Infections - Brain Under Siege
- Meningitis: Inflammation of meninges (fever, headache, nuchal rigidity).
- Encephalitis: Inflammation of brain parenchyma (altered sensorium, seizures, focal deficits).
- Meningoencephalitis: Overlap of both meningitis and encephalitis.
- Brain Abscess: Focal, encapsulated infection within parenchyma; presents with fever, focal signs, and features of raised ICP. Ring-enhancing lesions on imaging.
⭐ In Tuberculous Meningitis, CSF classically shows a spider-web coagulum (fibrin clot) on standing, with markedly elevated protein and lymphocytic pleocytosis.
Bacterial Meningitis - The Pus Peril
- CSF Analysis: Crucial for diagnosis.
| Feature | Bacterial | Viral | Tubercular (TBM) | Fungal |
|---|---|---|---|---|
| Appearance | Turbid/Purulent | Clear | Cobweb, Fibrin web | Viscous, Clear |
| Cells (/μL) | >1000 (↑↑ PMNs) | <1000 (↑ Lympho) | 100-500 (↑ Lympho) | <500 (↑ Lympho) |
| Protein | ↑↑ (>100 mg/dL) | N / ↑ | ↑↑ (>150 mg/dL) | ↑ |
| Glucose | ↓↓ (<40 mg/dL) | Normal | ↓ (<45 mg/dL) | ↓ |
- **Neonate (<1 mo):** *E. coli*, Group B Strep, *Listeria*. (📌 **GEL**)
- **1 mo - 5 yr:** *S. pneumoniae*, *N. meningitidis*, *H. influenzae*.
- **>5 yrs:** *S. pneumoniae*, *N. meningitidis*.
⭐ Dexamethasone (0.15 mg/kg) is given before or with the first antibiotic dose in children >6 weeks to reduce sensorineural hearing loss, especially in Hib & pneumococcal meningitis.
- Empirical Antibiotic Therapy Flowchart:
TB Meningitis - The Slow Burn
- Onset: Insidious, subacute progression over 2-8 weeks. Prodrome of low-grade fever, malaise, headache.
- Staging (MRC): Stage 1 (Alert), Stage 2 (Lethargic, CN palsies), Stage 3 (Coma, seizures).
- CSF Analysis: Classic triad of ↑ lymphocytes, ↑↑ protein (>100 mg/dL), ↓ glucose (<45 mg/dL). Fibrin web / cobweb coagulum on standing.
- Imaging (CT/MRI): Basal exudates, hydrocephalus, tuberculomas, infarcts.
- Treatment: Anti-tubercular therapy (ATT) + corticosteroids (prednisolone) to reduce inflammation.
⭐ High-Yield: Thick, gelatinous exudates at the base of the brain are pathognomonic, leading to cranial nerve palsies (esp. VI) and obstructive hydrocephalus.
Viral Infections - Ghost In The Machine
- Aseptic Meningitis: Most common viral CNS infection. Predominantly caused by Enteroviruses (Coxsackie, Echovirus) and Mumps.
- CSF: Lymphocytic pleocytosis, normal glucose, sterile on bacterial culture.
- Encephalitis: Inflammation of the brain parenchyma.
| Feature | Herpes Simplex Encephalitis (HSV-1) | Japanese Encephalitis (JE) |
|---|---|---|
| Clinical | Acute fever, focal seizures, altered sensorium | Parkinsonian rigidity, tremors, mask-like facies |
| CSF | ↑ RBCs, lymphocytic pleocytosis | Similar to aseptic meningitis |
| Imaging | Temporal lobe hemorrhagic necrosis | Thalamic, basal ganglia involvement |
Neonatal Meningitis - A Fragile Start
- Common Pathogens: Group B Strep (S. agalactiae), E. coli, Listeria monocytogenes. 📌 Mnemonic: GEL.
- Clinical Signs: Non-specific and subtle. Includes fever/hypothermia, poor feeding, lethargy, irritability, seizures, or a tense, bulging fontanelle.
- Empirical Treatment: Ampicillin (for Listeria) + Gentamicin (synergy) OR Cefotaxime (better CNS penetration).
⭐ In late-onset meningitis (after 72 hours), Staphylococcus and gram-negatives are more common; consider Vancomycin.
- Neonatal meningitis is caused by GBS, E. coli, & Listeria. In infants/children, it's S. pneumoniae.
- Bacterial CSF: ↑ neutrophils, ↑ protein, ↓ glucose. Viral CSF: ↑ lymphocytes, normal glucose.
- Tuberculous meningitis: Lymphocytic CSF, markedly ↑ protein, ↓ glucose, and cobweb coagulum.
- HSV encephalitis causes hemorrhagic necrosis of the temporal lobes; treat with IV Acyclovir.
- Japanese Encephalitis shows extrapyramidal features and bilateral thalamic lesions.
- Dexamethasone is vital in Hib meningitis to prevent sensorineural hearing loss.
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