What is Encephalitis?

Encephalitis is a rare inflammation of the white and gray matter of the brain. Although it technically refers to any brain inflammation, the term encephalitis is most commonly used to describe inflammation caused by a viral infection.

Arthropod-borne viruses (arboviruses) play a significant role in the spread of encephalitis worldwide. Arthropods are insects and insect-like animals with a hard outer skeleton and jointed limbs, such as mosquitoes and ticks. Birds and mammals serve as hosts of the virus. A mosquito feeding on an infected animal becomes an encephalitis carrier for the remainder of its short life. The virus is then passed by the mosquito to other animals it feeds on, which, in turn, infects other mosquitoes feeding on that animal. Reptiles, amphibians and (in rare cases) humans also can serve as hosts of viruses that cause encephalitis. In most cases, the virus requires a vector and is not transmitted directly from one infected animal to another.

Viral infection can occur either directly in the brain and spinal cord (primary encephalitis) or spread to these areas from elsewhere in the body (secondary or postinfectious encephalitis). It is also possible, though uncommon, to contract encephalitis through other organisms, such as bacteria, fungi or parasites.

A swollen or irritated brain will not maintain normal blood flow, usually causing ailments such as fever, headache or confusion. Frequently, the root cause of encephalitis can also agitate or inflame frail tissue structures lining the brain and spinal cord (meninges). When the meninges become inflamed, this condition is known as meningitis. Encephalitis and meningitis often occur simultaneously, a condition called meningoencephalitis. In addition, encephalitis may be a complication of meningitis that is untreated, spreading infection from the meninges to brain. When the spinal cord is also affected, the term encephalomyelitis may be used.

Most cases of encephalitis are mild and may not even produce noticeable symptoms. Encephalitis is most hazardous to infants, elderly people, individuals with weakened immune systems (e.g., cancer or HIV/AIDS patients) or people who live in areas with high mosquito populations. However, the disease can be potentially severe or even fatal to people of all ages.

How is it diagnosed?

Having a physician compile a patient's medical history and perform a physical examination are the first steps toward diagnosing encephalitis. Secondary (postinfectious) encephalitis may be suspected if symptoms appear after contraction of another viral infection (e.g., after contracting a herpes infection).

Tests used to diagnose encephalitis may include:

• Spinal tap (also known as a lumbar puncture). Involves inserting a needle directly into the lower spine area to extract fluid for laboratory testing. A spinal tap is the most common method used to diagnose encephalitis. Advances in the testing of DNA (the material that carries an organism's genetic information) have made it possible to diagnose encephalitis through more detailed examination of spinal fluids. This may reveal the presence of the responsible organism or signs of general infection (e.g., a heightened white blood cell count that indicates the body is fighting infection).
• Blood testing. Removal of a sample of blood (usually from a vein) for laboratory analysis. Certain causes of encephalitis, such as the West Nile virus, are detectable through blood testing. Analysis of blood may show a rise in antibodies to a particular virus or other indicators necessary to make a diagnosis. In some cases, other blood tests may be performed such as a polymerase chain reaction (PCR) to identify the virus' DNA or by culturing a specific virus found in the blood.
• Brain imaging. A CAT (computed axial tomography) scan or MRI (magnetic resonance imaging) that produces images of the brain may reveal swelling consistent with encephalitis. Pressure within the brain can often be observed through brain imaging, providing valuable insight about the likelihood of encephalitis infection prior to performing a spinal tap. Some imaging tests may be more appropriate than others. For example, MRI is typically preferred over CAT scans as a method of diagnosing herpes simplex virus type 1 (HSV-1) encephalitis. This is because CAT scans may appear normal during the initial days of illness, when the effectiveness of therapy is likely to be greatest.
• Electroencephalography (EEG). A measure of the brain's electrical activity. Electrodes that monitor electrical impulses of the brain are pasted or otherwise attached to the scalp. The electrodes send brain activity information to a special machine where it is recorded on paper. Abnormal readings may indicate the presence of encephalitis. However, normal results do not necessarily rule out the presence of encephalitis infection.
• Brain biopsy. Removal of a sample of brain tissue for laboratory analysis. The patient is anesthetized and a small hole is drilled into the skull, followed by the insertion of a needle into the brain tissue. Computer–imaging techniques such as x-rays or MRI aid in this technique. A brain biopsy may be necessary in rare instances when diagnosis of encephalitis through other methods is not possible. This test has significant risks and is not commonly performed.

How is Encephalitis treated?

Treatment for a mild case of encephalitis consists primarily of supportive care, such as rest, maintaining a nutritious diet and drinking plenty of liquids. Over-the-counter pain relieving medications can reduce symptoms such as headaches and fever. The use of anti-inflammatory drugs may reduce puffiness or pressure in the head. Children and teens with encephalitis should not be given aspirin. Aspirin used after a viral infection can cause Reye syndrome, a rare but sometimes fatal condition.

More serious cases of encephalitis may require different types of treatment. Early therapy that is targeted at the specific nature of the illness can substantially reduce the likelihood of bodily damage and death. Delayed treatment is usually associated with a poorer prognosis. Patients with severe encephalitis may require hospitalization.

Treatment of serious cases of encephalitis may include:

• Antibiotics are recommended. Although the infection may be viral, antibiotics can prevent an additional bacterial infection.
• Antiviral therapy can be used for certain viruses (e.g., herpes simplex virus) susceptible to antiviral drugs. However, antiviral compounds have yet to be developed for all viruses (e.g., arboviruses).
• Anticonvulsant medications can help with seizures.
• Corticosteroids may be used to help reduce brain swelling and inflammation.
• Nutritional supplements or feeding tubes may be needed.
• Lights may be dimmed to help alleviate headaches, but not enough to create shadows, which may cause hallucinations.
• Rehabilitative treatment (e.g., speech therapy, physical therapy, occupational therapy) can address lasting damage, such as behavioral changes or problems with physical mobility or function. Such treatment may be needed for some pediatric cases of encephalitis. Children under one year of age are more likely to experience neurological complications such as seizures, paralysis and developmental delays.

The prognosis for patients following treatment varies. Patients who experience mild cases of encephalitis typically experience an acute phase that lasts for up to two weeks before they slowly make a full recovery, without treatment. On the other hand, permanent impairment or death are sometimes associated with more severe cases.

Medications

What might complicate it?

Possible complications include seizures, demyelinating conditions (causing loss of sensation, coordination, and power in specific areas of the body), and death. The meninges (membranes that cover and enclose the brain) may also be involved, causing meningoencephalitis.

Alternatives

Conditions with similar symptoms include meningitis, cerebral abscess, septic emboli, cortical septic thrombophlebitis, toxic encephalopathies, subdural and subarachnoid hemorrhage, porphyria, and multiple sclerosis.

Rehabilitation

Physical therapy and/or occupational therapy, three to five times a week, for a period of six to twelve weeks.

Appropriate specialists

Neurologist, infectious disease specialist, physical therapist, and speech therapist.

Last updated 1 July 2015