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HSV Encephalitis

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HSV Encephalitis, Herpes Simplex Encephalitis

  • Epidemiology
  1. Most common cause of sporadic focal Encephalitis (1 per 250,000)
  2. HSV is responsible for 10% of Encephalitis cases
  3. Newborns: Onset 2-30 days after delivery
  4. Bimodal distribution of onset
    1. Age under 20 years old (33% of cases)
    2. Age over 50 years old (>50% of cases)
  • Etiology
  1. Adults
    1. Herpes Simplex Virus Type I
    2. Herpes Simplex Virus Type II (rare)
  2. Neonates
    1. See Neonatal HSV
    2. Perinatal Herpes Simplex Virus Type II transmission
  • Pathophysiology
  1. Encephalitis (brain inflammation)
  2. HSV Encephalitis causes inflammation, Hemorrhage and edema
  3. Results in brain necrosis and liquefaction
  4. Destructive lesions by HSV infection
    1. Inferior Frontal Lobe
    2. Anterior Temporal Lobe
  • Precautions
  1. Fever, Headache and neurologic abnormalities should prompt evaluation for Encephalitis
  2. Worse outcomes with delayed diagnosis
  3. Cryptic presentations
    1. Skin vessicles may be absent
    2. Nuchal Rigidity may be absent
    3. Fever alone may be only presenting finding
    4. Neurologic changes may be subtle (mild behavior change or mild cognitive deficits)
  • Symptoms
  1. Fever
  2. Headache
  3. Irritability and decreased feeding in newborns
  4. Lethargy
  5. Tremors
  6. Focal Seizures
  7. Ataxia
  8. Vomiting
  9. Dysphagia
  10. Altered Mental Status
    1. Behavioral changes
    2. Memory changes
    3. Personality Changes
  • Labs
  1. See Encephalitis
  2. Lumbar Puncture for CSF
    1. CSF PCR for HSV (gold standard)
      1. Test Sensitivity: 95%
      2. False negatives occur in first 12 hours and after 10 days
    2. CSF Cell Count
      1. Test Sensitivity: 95% for Pleocytosis at 10-200 cells
      2. Predominantly Lymphocytosis or monocytosis
      3. Xanthochromia and Red Blood Cells may be present
    3. CSF Protein
      1. Increased to 100 mg/dl in 80% of cases
    4. CSF Glucose
      1. Normal to low
  • Diagnosis
  1. MRI Head imaging
    1. MRI is preferred over CT Head (CT Head is typically normal in first 5 days)
    2. Diffuse edema
    3. Medial temporal and inferior Frontal Lobe necrotic changes on imaging
      1. T1 weighted images - hypointensity
      2. T2 weighted images - hyperintensity
  2. Electroencephalogram (EEG)
    1. Findings localize to frontal and Temporal Lobe
    2. Periodic sharp wave activity temporally
    3. Background of focal or diffuse slowing
  • Management
  1. See Encephalitis
  2. Acyclovir
    1. Dose (adjust for decreased Renal Function)
      1. Age under 12 years: 20 mg/kg IV every 8 hours
      2. Age over 12 years: 12.5 mg/kg IV every 8 hours
    2. Duration: 14-21 days (or until HSV Encephalitis is excluded)
    3. Directions: Give dose over 60 minutes
    4. Start early, empirically, as soon as diagnosis is considered possible, to maximize best possible outcome
      1. Initially, Acyclovir is also added to Meningitis antibiotic regimen until HSV Encephalitis is excluded
  • Complications
  • Prognosis
  1. Mortality: 10-40%
    1. Acyclovir has reduced mortality from >70% to <20%
  2. High risk of severe residual neurologic deficit
  • References
  1. Claudius in Majoewsky (2012) EM:Rap 12(11): 7-8
  2. Fuchs and Yamamoto (2012) APLS, Jones and Bartlett, Burlington, p. 180-3
  3. Herbert and Jhun in Herbert (2014) EM:Rap 14(12):12