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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 result in the clinical syndromes of aseptic meningitis or encephalitis [1-3]. The true incidence of these infections is difficult to determine because many cases are unreported, the diagnosis may not be considered, 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].

This topic will review the major distinguishing features between aseptic meningitis and viral encephalitis, as well as the viral etiologies that can cause encephalitis. Topic reviews that discuss the clinical manifestations, diagnosis, and pathogens associated with aseptic meningitis in adults and viral encephalitis in children are found elsewhere. (See "Aseptic meningitis in adults" and "Acute viral encephalitis in children: Clinical manifestations and diagnosis" and "Acute viral encephalitis in children: Treatment and prevention" and "Acute viral encephalitis in children: Pathogenesis, incidence, and etiology".)


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 a differentiating feature, 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.

However, the distinction between the two entities can be frequently blurred since some patients may have both a parenchymal and meningeal process with clinical features of both. The patient is usually labeled as having meningitis or encephalitis based upon which features predominate in the illness although meningoencephalitis is also a common term that recognizes the overlap. The importance of distinguishing between encephalitis and aseptic meningitis relates to the fact that the likely cause of each syndrome is different. Some viral agents are more likely to cause aseptic meningitis, and others are more likely to cause encephalitis (See "Aseptic meningitis in adults".)


Viral encephalitis can be either primary or postinfectious (ie, it occurs after the infection has resolved) [5].

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Literature review current through: Oct 2017. | This topic last updated: Oct 15, 2017.
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