Types of Traumatic Brain Injuries: Encephalitis

Encephalitis

What is encephalitis?

Although the term "encephalitis" literally means "inflammation of the brain," it usually refers to brain inflammation resulting from a viral infection. The severe and potentially life-threatening form of this disease is rare. Experts suspect that the actual incidence of encephalitis is probably much higher — but because most people have such mild signs or symptoms, many cases go unrecognized.

Encephalitis occurs in two forms — a primary form and a secondary form. Primary encephalitis involves direct viral infection of your brain and spinal cord. In secondary encephalitis, a viral infection first occurs elsewhere in your body and then travels to your brain.

What causes encephalitis?

The most common cause in the United States is the herpes simplex virus, the same virus that causes cold sores and genital herpes. Other common viruses that may cause encephalitis include those that cause mumps, measles, chickenpox, mononucleosis (Epstein-Barr virus), influenza, and German measles (rubella). These viruses usually lead to less serious illnesses, but on rare occasions, they infect the brain and cause encephalitis.

Another group of viruses, called arboviruses, can spread encephalitis mainly through bites from mosquitoes and ticks. Most people who are bitten by infected mosquitoes or ticks do not develop any symptoms, and only a very small number of people who develop symptoms of infection from arboviruses actually develop encephalitis. In the U.S., encephalitis caused by arboviruses tends to occur in the summer and early fall when mosquitoes and ticks are biting and people are spending more time outdoors.

Although very rare, infection with the rabies virus can also lead to encephalitis that is almost always fatal if not treated before symptoms develop.

What are the symptoms?

It is important to seek immediate medical attention if you suspect that you have encephalitis. The key symptoms are fever, severe headache, and confusion. Other symptoms that may occur include:

• Abnormal sensitivity to light (photosensitivity).
• Nausea and vomiting.
• Stiff neck and back.
• Lack of energy, sluggishness (lethargy).
• Drowsiness.

More serious symptoms can also develop, including;

• Seizures or tremors.
• Personality changes.
• Memory loss.
• Trouble learning and understanding.
• Restlessness.
• Confused speech.
• Hallucinations, which is seeing or hearing things that aren't there.
• Delirium, which is a sudden change in your mental status, leading to confusion and unusual behavior.
• The most severe form of encephalitis can lead to coma and even death, especially if left untreated. In general, symptoms that develop suddenly and are severe from the start are more likely to progress to a life-threatening case of encephalitis.

While complications such as speech or memory problems can occur, most people fully recover from encephalitis when treated promptly. However, your chances for a full recovery decrease if you have severe symptoms such as seizures or coma or if you delay treatment.

The early stage of encephalitis may cause symptoms similar to meningitis, a serious viral or bacterial illness that causes inflammation of the tissues that surround the brain and spinal cord.

How is encephalitis diagnosed?

Lab tests that may be used to diagnose encephalitis include the following:

• Spinal fluid analysis
  • An analysis of the fluid in the spine (cerebrospinal fluid) is one of the most important tests in diagnosing encephalitis. Samples are taken during a lumbar puncture (spinal tap), in which a needle is inserted in the lower back between the bones of the spine. The spinal fluid is examined for evidence of infection, such as increases in white blood cells and protein. In the case of herpes simplex encephalitis, health professionals can test for traces of the virus's genetic material. Also, your health professional may do a viral culture to identify the virus causing encephalitis. For a viral culture, a small amount of the fluid is placed in a container with other cells that grow a virus. It may take several weeks before the results of a viral culture are known.
• Imaging tests
  • Magnetic resonance image (MRI) of the head may be used to detect specific areas of inflammation or bleeding in the brain caused by encephalitis. However, most people with encephalitis have normal MRIs.
  • Another imaging test, computed tomography (CT) of the head and face, also may be used to see these changes in the brain. A CT scan uses X-rays to take pictures of the brain. See an illustration of a CT of encephalitis.
• Blood tests
  • Testing for antibodies in the blood can identify some causes of encephalitis, including mosquito-borne viruses and the viruses that cause mononucleosis (Epstein-Barr virus), cytomegalovirus, and toxoplasmosis.
• Electroencephalogram (EEG)
  • An electroencephalogram (EEG) can help confirm a diagnosis of encephalitis. An EEG records electrical activity in the brain through wires (electrodes) taped to your head and hooked up to a computer. If you have encephalitis, the EEG may show an abnormal increase or decrease in electrical activity; however, an EEG does not indicate whether the abnormal electrical activity is caused by encephalitis.
• Brain biopsy
  • Brain biopsy sometimes may be used to find the cause of encephalitis, especially if herpes simplex encephalitis is suspected and you do not appear to be improving after treatment with acyclovir (an antiviral medication used to treat the herpes simplex virus). An MRI may also help guide the health professional in determining which tissue to biopsy should a biopsy be needed. Using MRI to guide the biopsy needle, the doctor removes a small sample of brain tissue and examines it for viral infection. Brain biopsy is seldom used because tests of blood and spinal fluid usually can accurately diagnose encephalitis caused by the herpes simplex virus.

How is it treated?

You will probably be treated for encephalitis in a hospital's intensive care unit. During your stay, your vital signs (blood pressure, heart rate, breathing, and level of body fluids) will be closely monitored. Treatment will depend upon your symptoms and the particular cause of encephalitis, if the cause can be determined.

Encephalitis caused by the herpes simplex virus or the chickenpox (varicella-zoster) virus is treated with the antiviral medication acyclovir, which is given in a vein (intravenous, or IV). Because early treatment can increase your chances of recovery, it is important to start acyclovir treatment as soon as encephalitis is suspected, even if the exact cause of the illness is unknown. With early treatment, 70% of those with herpes simplex encephalitis recover. Treatment works best when given within 4 days of the start of the illness. Call your doctor immediately if you think you have symptoms of encephalitis such as a sudden and severe headache, fever, and confusion, especially if accompanied by a stiff neck, nausea, vomiting, and drowsiness.

Some health professionals also are using the herpes zoster (shingles) medication valacyclovir for herpes simplex encephalitis, even though this medication has not officially been approved for the treatment of encephalitis (unlabeled use).

Encephalitis caused by arboviruses, which are carried by mosquitoes and ticks, will not respond to acyclovir or other medications. Instead of trying to kill the virus, doctors treat the symptoms so you are comfortable and the body can heal itself.

High fever may be reduced with acetaminophen (Tylenol) or nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, aspirin, or naproxen. However, a mild fever may actually promote healing and is usually not treated. Aspirin should not be given to anyone younger than 20 because of the risk of Reye's syndrome.

Seizures may be controlled with anticonvulsant medications such as phenytoin (Dilantin) or phenobarbital. A machine to help you breathe (ventilator) and other supportive measures may be needed if you go into a coma.

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