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Definition
Encephalitis is an inflammation (irritation and swelling) of the brain, usually caused by infections. See also meningitis.Causes, incidence, and risk factors
Encephalitis is most often caused by a viral infection, and many types of viruses may cause it. Exposure to viruses can occur through insect bites, food or drink contamination, inhalation of respiratory droplets from an infected person, or skin contact. In rural areas, arboviruses -- carried by mosquitoes or ticks, or accidentally ingested -- are the most common cause.
In urban areas, enteroviruses are most common, including coxsackievirus, poliovirus, and echovirus. Other causes include herpes simplex infection, varicella (chickenpox or shingles), measles, mumps, rubella, adenovirus, rabies, West Nile virus, and extremely rarely, vaccinations.
Once the virus has entered the bloodstream, it may localize in the brain, causing inflammation of brain tissue and surrounding membranes. White blood cells invade the brain tissue as they try to fight off the infection.
The brain tissue swells (cerebral edema), which may cause destruction of nerve cells, bleeding within the brain (intracerebral hemorrhage), and brain damage.
Encephalitis is uncommon. It affects approximately 1,500 people per year in the U.S. The elderly and infants are more vulnerable and may have a more severe course of the disease.
Symptoms
Signs and tests
Various symptoms resembling meningitis may be present. An examination may show signs of meningeal irritation (especially neck stiffness), increased intracranial pressure, or other neurologic symptoms such as muscle weakness, mental confusion, speech problems, and abnormal reflexes. The patient may have a skin rash, mouth ulcers, and signs of involvement of other organs such as the liver and lungs.Treatment
The goals of treatment are to provide supportive care and relieve symptoms. Antiviral medications may be prescribed for herpes encephalitis or other severe viral infections. Most of the time, however, no specific antiviral drugs are available to combat the infection.
Antibiotics may be prescribed when the infection is caused by some organisms, such as certain bacteria. Anti-seizure medications (such a phenytoin) are used to suppress seizures. On rare occasions, potent anti-inflamatory drugs called steroids (such as dexamethasone) are used to reduce brain swelling.
Sedatives may be needed to treat irritability or restlessness. Other medications, like acetaminophen, may be used for fever and headache.
Supportive care (rest, nutrition, fluids) allows the body to fight the infection. Reorientation and emotional support of confused or delirious persons may be helpful.
If brain function is severely affected, interventions like physical therapy and speech therapy may be necessary after the acute illness is controlled.
Expectations (prognosis)
The outcome varies. Some cases are mild, short, and relatively benign followed by full recovery. Other cases are severe, and permanent impairment or death is possible.Complications
Permanent neurologic impairments to memory, speech, vision, hearing, muscle control, or sensation may occur in people who survive severe cases of encephalitis.Calling your health care provider
Go to the emergency room or call the local emergency number (such as 911) if sudden fever, neurologic changes, and other symptoms suggestive of encephalitis occur.Prevention
Controlling mosquitoes (a mosquito bite can transmit some viruses) may reduce the chance of some infections that can lead to encephalitis.
Animal vaccination is important to prevent encephalitis caused by rabies virus. Vaccination is available to prevent a form of viral encephalitis that often affects people living in dorms or in the military.
Update Date: 8/10/2004 Updated by: Joseph V. Campellone, M.D., Division of Neurology, Cooper University Hospital, Camden, NJ. Review provided by VeriMed Healthcare Network.
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Page last updated: 28 October 2004 |