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Encephalitis in-ˌsef-ə-ˈlīt-əs

By John E. Greenlee, MD

Encephalitis is inflammation of the brain that occurs when a virus directly infects the brain or when a virus, vaccine, or something else triggers inflammation. The spinal cord may also be involved, resulting in a disorder called encephalomyelitis.

  • People may have a fever, headache, or seizures, and they may feel sleepy, numb, or confused.

  • Magnetic resonance imaging of the head and a spinal tap are usually done.

  • Treatment involves relieving symptoms and sometimes using antiviral drugs.

Encephalitis is most commonly due to viruses, such as herpes simplex, herpes zoster, cytomegalovirus, or West Nile virus. It can occur in the following ways:

  • A virus directly infects the brain.

  • A virus that caused an infection in the past becomes reactivated and directly damages the brain.

  • A virus or vaccine triggers a reaction that makes the immune system attack brain tissue (an autoimmune reaction).

Sometimes bacteria cause encephalitis, usually as part of bacterial meningitis (called meningoencephalitis).

Protozoa, such as amebas, those that cause toxoplasmosis (in people who have AIDS), and those that causes malaria, can also infect the brain and cause encephalitis.

Rarely, encephalitis develops in people who have cancer—a disorder called paraneoplastic encephalitis. This type of encephalitis appears to result from the immune system's response to the tumor.

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