What is encephalitis?

Updated: Aug 07, 2018
  • Author: David S Howes, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Answer

Encephalitis, an inflammation of the brain parenchyma, presents as diffuse and/or focal neuropsychological dysfunction. Although it primarily involves the brain, the meninges are frequently involved (meningoencephalitis).

From an epidemiologic and pathophysiologic perspective, encephalitis is distinct from meningitis, though on clinical evaluation both can be present, with signs and symptoms of meningeal inflammation, such as photophobia, headache, or stiff neck. It is also distinct from cerebritis. Cerebritis describes the stage preceding abscess formation and implies a highly destructive bacterial infection of brain tissue, whereas acute encephalitis is most commonly a viral infection with parenchymal damage varying from mild to profound.

Although bacterial, fungal, and autoimmune disorders can produce encephalitis, most cases are viral in origin. The incidence of encephalitis is 1 case per 200,000 population in the United States, with herpes simplex virus (HSV) being the most common cause. Considering the subacute and chronic encephalopathies, the emergency department (ED) physician is most likely to encounter toxoplasmosis in an immune-compromised host.


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