Herpes simplex encephalitis

Background

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

Microbiology

• More commonly caused by HSV-1 than HSV-2 (which more commonly causes aseptic meningitis)

Pathophysiology

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

Epidemiology

• Causes about 10% of encephalitis cases

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

• Other causes of encephalitis

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