Meningitis and Encephalitis

M&E Intro & Etiology - Brain Under Siege

• Meningitis: Inflammation of meninges (pia, arachnoid, dura).
• Encephalitis: Inflammation of brain parenchyma itself.
• Meningoencephalitis: Concurrent inflammation of both meninges and brain.

Key Etiological Agents:

• Bacteria: Most common cause of pyogenic meningitis.
• Viruses: Common cause of aseptic meningitis and encephalitis.
• Fungi: Typically in immunocompromised individuals (e.g., Cryptococcus).
• TB: Causes chronic granulomatous meningitis.

Common Bacterial Etiology by Age:

M&E Clinical Features - Spotting the Alarms

• General: Fever, headache, irritability, vomiting. Infants: poor feeding, high-pitched cry, lethargy.
• Meningeal Signs:
  • Nuchal rigidity.
  • Kernig's sign: 📌 Knee extension painful with hip flexed.
  • Brudzinski's sign: 📌 Bending neck flexes hips/knees.
  • Bulging fontanelle (infants).
• Alarm Bells (Red Flags):
  • Rapid deterioration.
  • Seizures, focal neurological deficits.
  • Papilledema.
  • Shock.
  • Petechial/purpuric rash (⚠️ meningococcemia).

⭐ Classic triad of meningitis: fever, nuchal rigidity, altered mental status (often incomplete, especially in infants).

M&E Diagnosis - Decoding CSF Clues

• Lumbar Puncture (LP): Key diagnostic. CSF if no contraindications (↑ICP signs, coagulopathy). CT head prior if focal deficits/papilledema.

• CSF Analysis Table:

  Feature	Bacterial	Viral	TB	Fungal
  Appearance	Turbid	Clear	Viscous, cobweb	Variable
  Cells (WBC/µL)	>1k PMN	10-500 Lymph	100-500 Lymph	<500 Lymph
  Protein (mg/dL)	↑↑ >100	N/↑ <100	↑↑ >100	↑
  Glucose (mg/dL)	↓↓ <40 (Ratio <0.4)	N (Ratio >0.6)	↓ <45 (Ratio <0.5)	↓
  Key Tests	Gram, Culture	PCR	AFB, PCR, ADA	India Ink, CrAg

⭐ India Ink for Cryptococcus neoformans (encapsulated yeast) in CSF is classic.

• Neuroimaging (CT/MRI):

  • Rules out mass/↑ICP pre-LP.
  • Shows complications (hydrocephalus), meningeal enhancement.

• CSF Interpretation Flow:

M&E Management & Prevention - Fighting & Shielding

Empirical Rx by Age:

Pathogens & Rx:

• ABCs, IV fluids, vitals.
• ICP: Head up, Mannitol (0.25-1 g/kg), 3% saline.
• Seizures: IV Lorazepam, then Phenytoin.
• Dexamethasone: 0.15 mg/kg q6h x2-4d (Hib).

  ⭐ Dexamethasone reduces hearing loss in Hib meningitis; give with/before 1st antibiotic dose.

Prevention:

• Vaccines: Hib, PCV, MenC, MMR, Varicella.
• Chemoprophylaxis (contacts): Rifampicin.

High‑Yield Points - ⚡ Biggest Takeaways

• Bacterial meningitis pathogens by age: Neonates (GBS, E.coli, Listeria); Children (S.pneumoniae, N.meningitidis).
• CSF in bacterial meningitis: ↑Protein, ↓Glucose, ↑Neutrophils, ↑Pressure. Viral: Normal Glucose, ↑Lymphocytes.
• Kernig's and Brudzinski's signs indicate meningeal irritation.
• Empirical antibiotics: Neonates (Ampicillin + Gentamicin/Cefotaxime); Older children (Ceftriaxone + Vancomycin).
• HSV encephalitis: Temporal lobe involvement is characteristic; treat promptly with Acyclovir.
• Most common meningitis sequela: Sensorineural hearing loss.
• Lumbar Puncture (LP) contraindications: Signs of markedly ↑ICP, shock, severe coagulopathy.