Encephalitis Definition and Characterization

Conceptual image of Encephalitis.
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Medical Specialties:

Family practice, Internal medicine, Neurology

Clinical Definition:

Encephalitis is a severe irritation and inflammation of the brain, usually due to infection. Most often, the infection is viral, such as the herpes simplex virus. Other causes include autoimmune disease, an allergic reaction to vaccines, bacteria and parasites, as well as the after-effects of cancer.

In Our Own Words:

Encephalitis, a severe and sometimes fatal inflammation of the brain, is most often caused by a virus.

While meningitis affects the protective membranes covering the brain (known as the meninges), encephalitis involves the brain tissue itself. Some patients may develop both. In viral encephalitis, fever, headache, low energy, and confusion are some possible symptoms. Brain scans, blood tests, and a lumbar puncture are among tests to diagnose encephalitis.

If caused by infection, possible treatment includes rest, fluids, and antiviral or antibiotic medication. The severity of encephalitis is variable, with some patients having a mild, short disease followed by a full recovery. Others are more severe, with permanent impairment or death.

More Information About Encephalitis

Both meningitis and encephalitis are terrifying diseases that can kill even the most healthy people. Many people who manage to survive these diseases go on to live with lifelong sequelae, such as seizures and loss of memory.

Every year, encephalitis affects about 7 of 100000 people.  Mostly when physicians and other healthcare professionals refer to "encephalitis," they are referring to the viral causes of the disease like HSV rather than less common bacterial and autoimmune causes.

Herpes virus or HSV-1 is a common virus that has infected most people--if you have ever had a cold sore or oral herpes, then you know what we're talking about.

In a small minority of healthy people, HSV-1 can also cause viral encephalitis.

Other common viral causes of viral encephalitis are the varicella zoster virus, which also causes chicken pox and shingles, and Epstein-Barr virus (EBV), which causes infectious mononucleosis or "mono."

Very rarely, viral encephalitis can be caused by arboviruses which are transmitted by the bite of a tick or mosquito. In the United States, arboviruses that infect people include St. Louis encephalitis virus, West Nile virus, and La Crosse virus.

People with encephalitis typically present with headache and fever and one or more of the following symptoms:

  • altered consciousness
  • abnormal behavior
  • new seizures
  • confusion
  • focal neurological deficits

Encephalitis is first suspected based on clinical observation and then supported using results from a spinal fluid analysis (spinal tap) and neuroimaging tests (MRI).

People with meningitis and encephalitis are typically admitted to the hospital and first observed and treated in an ICU setting.

These patients are at risk for brain swelling, seizures, and increased brain pressure. These patients are treated symptomatically. Such symptomatic treatment can include pain medications, antipyretic (antifever) medications, and medications used to treat nausea.

Longer-term treatment for viral encephalitis includes several days of antiviral medications (like acyclovir) and months of pain medications and amitriptyline, an antidepressant medication.


Harvard Health Publicaitons "Medical Dictionary of Health Terms." Accessed August 2013.

University of Maryland Medical Center. "Encephalitis." Updated May 2013. Accessed August 2013.

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