Viral encephalitis, a general overview

Need to differentiate from encephaloPATHY

  • Encephalopathy normally involves a change in mental status (seizure, somnolence, coma).
  • Fever and focal signs are normally not present in encephalopathy.
  • CSF is usually normal in encephalopathy.


  • Not always due to infection. Autoimmune encephalitis can happen (eg NMDA-receptor encephalitis).
  • There are many causes of viral encephalitis (herpes, dengue, JE virus, West Nile virus etc).
  • Subacute sclerosing panencephalitis
    – Very rare and chronic form of measles virus encephalitis
    – Long latent period (about 10 years)
    – Staging of symptoms: personality changes (stage 1) -> myoclonus and spasms (Stage 2 & 3) -> coma (stage 4)
    – Dx: MRI (will show T2-hyperintense lesion in parietal and temporal lobe, basal ganglia can be involved later)
    – Treatment: only curable if stage 1, using interferon and ribavirin
  • ADEM (Acute Disseminated Encephalomyelitis)
    – Clinically can look like multiple sclerosis but differ by age group (children), fever present & acute onset.
    – Vaccination has been implicated as the potential cause.
    – Autoimmune pathogenesis, NOT INFECTIOUS, causing demyelination of white mater
    – Dx: MRI (hyperintense lesions in white mater, basal ganglia, calloseptal interface is uncommon unlike in MS)
    – Open ring sign can be seen in T1 C+ (due to demyelination which stops at the gray-white mater border)

    Case courtesy of Dr Frank Gaillard, <a href=””></a&gt;. From the case <a href=”″>rID: 2576</a>- Treatment: immunosuppressive therapy (high doses of IV dexamethasone/methylprednisolone)
  • Specific drug therapies in viral encephalitis:
    – Aciclovir for HSV, VZV and Herpesvirus simiae
    – Ganciclovir for CMV post-transplant
    – Ribavirin: maybe in measles encephalitis and Nipah virus encephalitis

** In encephalopathy,

  • Most common causes: hepatic/uremic encephalopathy, malignant hypertension
  • Infections may also cause encephalopathy eg cerebral malaria, sepsis


Allan R. Tunkel, Carol A. Glaser, Karen C. Bloch, James J. Sejvar, Christina M. Marra, Karen L. Roos,
Barry J. Hartman, Sheldon L. Kaplan, W. Michael Scheld, and Richard J. Whitley. The Management of Encephalitis: Clinical Practice Guidelines by the Infectious Diseases Society of America. Clinical Infectious Diseases 2008; 47:303–27


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