Updated: 11/19/2016


Review Topic
  • A 42-year-old male presentswith confusion, headache, and fever. The patient is unable to answer questions. A head CT is negative for a space-occupying lesion or hemorrhage. An MRI is shown. A lumbar puncture is performed, with cerebral spinal fluid (CSF) analysis showing a lymphocytic pleocytosis and normal glucose. PCR of the CSF is positive for HSV-1.
  • Brain parenchymal infection
    • abnormalities in brain functioning are expected
      • e.g., altered mental status, changes in personality, problems with speech and movement
      • this distinguishes encephalitis from meningitis
  • Typically caused by infection
    • viral (most cases)
      • herpes simplex virus (HSV)  
        • most common cause
      • varicella virus (VZV)
      • epstein-barr virus (EBV)
      • measles, mumps, rubella
      • HIV
      • Japanese encephalitis virus
      • St. Louis encephalitis virus
      • West Nile virus
    • bacterial
      • toxoplasmosis
    • noninfectious
      • acute disseminated encephalitis
  • There can be both an infection of the brain parenchyma and meninges
    • leading to a meningoencephalitis
  • Symptoms  
    • seizues
    • fever
    • headache
    • nausea
    • vomiting
  • Physical exam
    • altered mental status
    • personality changes
    • focal neurological deficits
      • cranial nerve palsies
      • hemiparesis.
    • meningsmus
      • only in pure encephalitis
  • CT scan of the head
    • MRI is the preferred imaging modality for HSV encephalitis
  • Lumbar puncture
    • perform after head imaging
    • PCR
      • most accurate for herpes encephalitis
  • Brain biopsy
    • last resort
    • only if etiology is unknown
  • Intracranial malignancy
    • primary or metastatic
  • Medication side-effects
  • Paraneoplastic or autoimmune disease
    • anti-NMDA receptor encephalitis
  • Treatment is dependent on etiology
    • HSV encephalitis
      • initiate acyclovir immediately
      • can be considered with VZV encephalitis
      • associated with a reduction in morbidity and mortality
      • foscarnet in acyclovir-resistant herpes
Prevention, Prognosis, and Complications
  • 50 - 75% mortality in untreated HSV encephalitis
  • < 1 or > 55 years old and immunocompromised is associated with poorer outcome

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