CNS Infections

Bacterial Meningitis - Pus Under Pressure

Life-threatening CNS emergency! Early diagnosis & treatment crucial.

CSF Analysis - Comparative Table:

• Neonates (<1mo): 📌 "LEGS" - Listeria, E. coli, Group B Strep.
• 1mo-12yr: S. pneumoniae, N. meningitidis, Hib (unimmunized).

• 12yr: N. meningitidis, S. pneumoniae.

Empirical Antibiotics (IV):

• Neonates: Ampicillin + Cefotaxime.
• 1mo-50yr: Vancomycin + Ceftriaxone.

• 50yr/Immunocompromised: Add Ampicillin (for Listeria). Duration: 7-21 days (organism-dependent).

⭐ CSF opening pressure is typically elevated (>180 mmH₂O) in bacterial meningitis.

Viral CNS & ADEM - Viral Invaders & Autoimmune Storms

• Viral (Aseptic) vs. Bacterial Meningitis (CSF Findings):

  Feature	Viral Meningitis	Bacterial Meningitis
  Opening Pressure	Normal / Slightly ↑	Markedly ↑
  WBCs	Lymphocytic pleocytosis	Neutrophilic pleocytosis
  Protein	Normal / Mildly ↑	Markedly ↑
  Glucose	Normal	↓ (often < 40 mg/dL)
  Gram Stain	Negative	Often Positive

• Herpes Simplex Encephalitis (HSE):

  • Most common cause of sporadic fatal encephalitis.
  • Key: Temporal lobe predilection, hemorrhagic changes.
  • Rx: Acyclovir 10-15 mg/kg IV q8h.

• Japanese Encephalitis (JE):

  • Flavivirus; mosquito vector (Culex).
  • Key: Extrapyramidal symptoms (parkinsonism, dystonia), thalamic lesions.
  • Prevention: Vaccination, mosquito control.

• Acute Disseminated Encephalomyelitis (ADEM):

  • Post-infectious/post-vaccinal immune-mediated demyelination.
  • MRI: Multifocal, asymmetric white matter lesions (often large, fluffy).
  • Rx: High-dose corticosteroids.

  ⭐ ADEM is typically monophasic; recurrent or multiphasic forms raise suspicion for Multiple Sclerosis (MS).

Chronic & Focal CNS Infections - Stealthy & Stubborn Foes

• Tuberculous Meningitis (TBM)
  • Stages: I (non-specific), II (meningism, CN palsies), III (coma, severe deficits).
  • CSF: Cobweb coagulum, ↑Protein (100-500 mg/dL), ↓Glucose (<45 mg/dL or <40% blood glucose), lymphocytes, ↑ADA (>10 U/L).
  • Rx: ATT (RHEZ) + Steroids (e.g., Dexamethasone 0.4 mg/kg/day).
  • Complications: Hydrocephalus, vasculitis, tuberculomas.
• Fungal Meningitis (esp. Cryptococcal)
  • Risk: Immunocompromised (HIV, steroids).
  • Dx: India ink stain (CSF), Cryptococcal antigen (CrAg) test.
  • Rx: Amphotericin B + Flucytosine, then Fluconazole.
• Neurocysticercosis (NCC)
  • Commonest parasitic CNS infection in India.
  • Stages: Vesicular → Colloidal → Granular → Calcified.
  • Presentation: Seizures (most common).
  • Rx: Albendazole (15 mg/kg/day) + Steroids (for viable cysts).

  ⭐ Scolex seen within the cyst in the vesicular stage on imaging is pathognomonic for NCC.

• Brain Abscess
  • Predisposing: Otitis, sinusitis, dental sepsis, CHD.
  • Classic triad (often incomplete <50%): Fever, headache, focal deficits.
  • Imaging: Ring-enhancing lesion on CT/MRI.
  • Rx: IV antibiotics +/- surgical drainage.

Neonatal & Congenital CNS Infections - Early Onset Onslaught

• Neonatal Meningitis:
  • Onset: Early (<7 days), Late (7-90 days).
  • Pathogens: Group B Strep (GBS), E. coli, Listeria monocytogenes.
  • Signs: Subtle (fever, poor feeding, irritability, lethargy, seizures).
  • Rx: Empirical Ampicillin + Gentamicin or Cefotaxime.
• Congenital (TORCH) CNS Infections:
  • CMV: Periventricular calcifications, microcephaly, SNHL.
  • Toxoplasmosis: Classic triad (chorioretinitis, hydrocephalus, intracranial calcifications). 📌 Sabin-Feldman dye test.
  • Rubella: Microcephaly, cataracts, deafness, PDA, "blueberry muffin" rash.
  • HSV: Skin vesicles, encephalitis (temporal lobe), seizures.

⭐ CMV is the most common congenital infection.

High‑Yield Points - ⚡ Biggest Takeaways

• Neonatal meningitis: Pathogens: Group B Strep, E. coli, Listeria.
• Childhood bacterial meningitis: S. pneumoniae, N. meningitidis common; Hib (unvaccinated).
• CSF: Bacterial (↑protein, ↓glucose, PMNs); Viral (N/↑protein, N glucose, lymphocytes); TB (↑↑protein, ↓↓glucose, lymphocytes).
• Tuberculous meningitis: Basal exudates, cranial nerve palsies, hydrocephalus; CSF: markedly low glucose.
• Herpes Simplex Encephalitis: Hemorrhagic temporal lobe involvement; treat with IV Acyclovir.
• Bacterial meningitis sequelae: Sensorineural hearing loss (most common), seizures, hydrocephalus.
• Brain abscess: Ring-enhancing lesion; risk: cyanotic heart disease, sinusitis/otitis.