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Encephalitis

Definition

Encephalitis is swelling of the brain. The swelling may involve the whole brain, or just parts of the brain. Encephalitis may just occur in individuals (sporadic) or may affect many people in a particular area (epidemic).
Encephalitis
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Causes

Encephalitis is most often caused by a viral infection. In the United States, the most common cause of sporadic encephalitis is the herpes simplex virus (HSV). Epidemic causes of encephalitis are usually mosquito or tick-borne viruses.
The most common viruses that cause encephalitis include:
Not all encephalitis is caused by a virus. Some may be due to an overreaction of the immune system.

Risk Factors

Factors that may increase your chance of encephalitis include:
  • Living, working, or playing in an area where mosquito-borne viruses are common
  • Not being immunized against diseases such as:
    • Measles
    • Mumps
    • Chickenpox
    • Polio
  • Having cancer
  • Taking immunosuppressive medicines after organ transplant
  • Having AIDS
Newborns of mothers who have genital herpes simplex are at risk for herpes simplex encephalitis.

Symptoms

The symptoms may range from mild to severe. Severe symptoms can include permanent neurological damage. Encephalitis can also lead to death.
Milder symptoms include:
  • Fever
  • Weakness, severe fatigue
  • Headache
  • Sensitivity to light
  • Stiff neck and back
  • Vomiting
  • Muscle aches
  • Rash
  • Yawning
More severe symptoms may include:
  • Changes in consciousness
  • Personality changes
  • Confusion
  • Irritability
  • Seizures
  • Partial or complete paralysis
  • Progressive drowsiness
  • Trouble walking
  • Trouble speaking
  • Trouble swallowing

Diagnosis

The doctor will ask about your symptoms and medical history. A physical exam will be done.
Tests may include:
  • Blood tests—to look for signs of infection
  • Spinal tap (lumbar puncture)—to test cerebrospinal fluid (CSF) for signs of infection
  • CT and/or MRI scans of the head—to look for abnormal areas of enhancement, hemorrhage, or edema in the brain
  • Electroencephalogram (EEG)— to look for abnormal electrical activity in the brain
  • Brain biopsy—removal of a small sample of brain tissue to test for signs of infection

Treatment

Treatment is mostly supportive. It may include:
  • Antiviral drugs (such as intravenous acyclovir for herpes simplex encephalitis)—to potentially help shorten the duration of the illness
  • Steroid medicines—to decrease brain swelling
  • Diuretics such as mannitol—to decrease elevated intracranial pressure
  • Intubation with hyperventilation—to decrease elevated intracranial pressure and to maintain respiration and ventilation
  • Anticonvulsant medicines—to prevent and/or treat seizures

Prevention

Make sure that you and your children are vaccinated against preventable viral illnesses.

RESOURCES

Encephalitis Information Resource http://www.encephalitis.info

National Institute of Neurological Disorders and Stroke http://www.ninds.nih.gov

CANADIAN RESOURCES

Canadian Neurological Sciences Federation http://www.ccns.org

Health Canada http://www.hc-sc.gc.ca

References

Cecil RL, Goldman L, Bennett JC. Cecil Textbook of Medicine. 21st ed. Philadelphia, PA: WB Saunders Company; 2000.

Conn HF, Rakel RE. Conn's Current Therapy 2001. 53rd ed. Philadelphia, PA: WB Saunders Company; 2001.

Herpes simplex encephalitis. EBSCO Publishing DynaMed website. Available at: http://www.ebscohost.com/dynamed/. Updated June 12, 2012. Accessed September 20, 2012.

California encephalitis. EBSCO Publishing DynaMed website. Available at: http://www.ebscohost.com/dynamed/. Updated July 16, 2012. Accessed September 20, 2012.

Eastern equine encephalitis. EBSCO Publishing DynaMed website. Available at: http://www.ebscohost.com/dynamed/. Updated July 13, 2012. Accessed September 20, 2012.

West Nile Infection. EBSCO Publishing DynaMed website. Available at: http://www.ebscohost.com/dynamed/. Updated September 12, 2012. Accessed September 20, 2012.

Mandell GL, Bennett JE, Dolin R. Principles and Practice of Infectious Diseases. 6th ed. New York, NY: Churchill Livingstone; 2004.

Rosen P, Barkin RM, Danzl DF, et al. Emergency Medicine: Concepts and Clinical Practice. 4th ed. St. Louis, MO: Mosby-Year Book; 1999.

Samuels MA, Feske SK. Office Practice of Neurology. Philadelphia, PA: Churchill Livingstone; 2003.

Revision Information

  • Reviewer: Rimas Lukas, MD
  • Review Date: 09/2012 -
  • Update Date: 00/93/2012 -

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

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