Herpes simplex encephalitis

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Background

  • Infection of the brain parenchyma by HSV, with a predilection for temporal lobes

Microbiology

Pathophysiology

  • About one-third are from primary infection while two-thirds are from reactivation of latent infection

Epidemiology

Clinical Manifestations

  • Fever
  • Headache
  • Altered level of consciousness
    • Personality and behavioural changes
  • Focal neuro deficits
  • Seizures
  • Rapidly progressing and can lead to coma

Differential Diagnosis

Investigations

  • Imaging
    • CT head usually normal
    • MRI head can show T2 signal change in temporal lobes
  • Lumbar puncture
    • Elevated protein
    • Lymphocytosis (10-1000 WBCs)
    • Erythrocytes in 80% of cases ("hemorrhagic necrotizing meningoencephalitis")
    • Normal or slightly low glucose
    • HSV PCR is confirmatory
    • If PCR is negative but suspicion remains high, repeat LP in 3 to 7 days
  • EEG
    • Spikes and slow waves over involved areas
    • Periodic lateralized epiieptiform discharges (PLEDs)
    • Usually predominately over involved termporal lobe

Management

  • May need repeat LP if the first one is negative but suspicion is high
  • Acyclovir 10mg/kg q8h IV for 14 days
    • Ensure adequate hydration and adjust for renal function
    • May do longer 14-21 days in immunocompetent patients due to high risk of relapse

Prognosis

  • 15% recover completely
  • 20% have severe neurologic sequelae
    • Primarily dysnomia and impaired new learning
    • Also seizures, neuropsychiatric illnesses
  • 28% mortality even with treatment
  • Prognosis is worse with those who are older, are sicker at presentation, or have delayed treatment