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Viral encephalitis in adults

Stephen J Gluckman, MD
Section Editor
Martin S Hirsch, MD
Deputy Editor
Jennifer Mitty, MD, MPH


Viral infections of the central nervous system (CNS) result in the clinical syndromes of aseptic meningitis or encephalitis [1-3]. The true incidence of these infections is difficult to determine because the diagnosis may not be considered, many cases are unreported, or a specific viral etiology is never confirmed. However, these disorders occur with sufficient frequency that clinicians should be familiar with the clinical manifestations, diagnostic techniques, and therapeutic options [4].

Unfortunately, the clinical syndromes and results of routine laboratory tests are typically nonspecific. Thus, other infectious and noninfectious causes must be entertained when evaluating such patients, particularly those disorders that are treatable.

The major distinguishing features of aseptic meningitis and viral encephalitis will be reviewed here. The clinical manifestations, diagnosis, and pathogens associated with aseptic meningitis are discussed separately. (See "Aseptic meningitis in adults".)

Detailed information regarding various pathogens that cause encephalitis, like herpes simplex virus, is found separately. (See "Herpes simplex virus type 1 encephalitis" and "Nipah and Hendra viral encephalitis" and "St. Louis encephalitis" and "Japanese encephalitis: Epidemiology, diagnosis, treatment, and prevention" and "Arthropod-borne encephalitides".)


The presence or absence of normal brain function is the important distinguishing feature between encephalitis and meningitis. Patients with meningitis may be uncomfortable, lethargic, or distracted by headache, but their cerebral function remains normal. In encephalitis, however, abnormalities in brain function are expected, including altered mental status, motor or sensory deficits, altered behavior and personality changes, and speech or movement disorders. Seizures and postictal states can be seen with meningitis alone and should not be construed as definitive evidence of encephalitis. Other neurologic manifestations of encephalitis may include hemiparesis, flaccid paralysis, and paresthesias.


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Literature review current through: Sep 2016. | This topic last updated: Mar 21, 2016.
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