What Is Encephalitis? What Causes Encephalitis?

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Main Category: Neurology / Neuroscience
Also Included In: Infectious Diseases / Bacteria / Viruses
Article Date: 28 Oct 2009 - 4:00 PDT

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Encephalitis is acute inflammation (swelling up) of the brain resulting either from a viral infection or when the body's own immune system mistakenly attacks brain tissue. The most common cause is a viral infection. In medicine acute means it comes on abruptly; of abrupt onset, develops rapidly, and usually requires urgent care. Encephalitis occurs in 1 in every 1,000 cases of measles.

According to the CDC (Centers for Disease Control and Prevention), USA, encephalitis occurs in approximately 0.5 in every 1000,000 individuals, most of them children, elderly people and individuals with weakened immune systems. The NHS (National Health Service)NHS, UK places the figure at 1.5 cases per 100,000 people. Health authorities suspect incidence is higher than official figures because many cases go unreported when symptoms are mild.

Encephalitis generally begins with fever and headache. The symptoms rapidly worsen, and there may be seizures (fits), confusion, drowsiness and loss of consciousness, and even coma.

Encephalitis can be life-threatening, but this is very rare.

According to Medilexicon's medical dictionary:

Ancephalitis means inflammation of the brain.

When there is direct viral infection of the brain or spinal cord it is called primary encephalitis. Secondary encephalitis refers to an infection which started off elsewhere in the body and then spread to the brain.

What are the signs and symptoms of encephalitis?

A symptom is something the patient reports and feels, while a sign is something other people, including a doctor may detect. For example, a headache may be a symptom, while a rash may be a sign.

The affected patient typically has a fever, headache and photophobia (excessive sensitivity to light). There may also be general weakness and seizures.

Less common - the individual may also experience nuchal rigidity (neck stiffness), which can lead to a misdiagnosis of meningitis. There may be stiffness of the limbs, slow movements, and clumsiness. The patient may also be drowsy and have a cough.

The brain swells (becomes inflamed) as a result of the body's attempt to fight off the infections.

In more severe cases the person may experience very severe headaches, nausea, vomiting, confusion, disorientation, memory loss, speech problems, hearing problems, hallucinations, as well as seizures and possibly coma. In some cases the patient can become aggressive.

Signs and symptoms in infants (small babies) - encephalitis is harder to initially detect in infants. Parents or guardians should look out for vomiting, a bulging fontanel (soft area on the top center of the head), incessant crying that does not get better when the baby is picked up and comforted, and body stiffness.

What are the causes of encephalitis?

Encephalitis can develop as a result of a direct infection to the brain by a virus, bacterium or fungus (infectious encephalitis, or primary encephalitis), or when the immune system responds to a previous infection; the immune system mistakenly attacks brain tissue (secondary encephalitis, or post-infectious encephalitis).

Primary (infectious) encephalitis: according to the NHS (UK), there are three main categories of viruses: 1. Common viruses, such as HSV (herpes simplex virus) or EBV (Epstein Barr virus). 2. Childhood viruses, such as measles and mumps. 3. Arboviruses, which are spread by mosquitoes, ticks and other insects, and include Japanese encephalitis, West Nile encephalitis and tick borne encephalitis.

Secondary (post-infectious) encephalitis: could be caused by a complication of a viral infection. Symptoms start to appear days and even weeks after the initial infection. The patient's immune system treats healthy brain cells as foreign organisms that need to be destroyed, and attacks them. We don't know why the immune system goes wrong and does this.

Encephalitis is more likely to affect children, elderly people, individuals with weakened immune systems, and people who live in areas where mosquitoes and ticks that spread specific viruses are common.

How is encephalitis diagnosed?

Doctors who identify classic symptoms in adults of fever, headache, confusion and occasionally seizures, and irritability, poor appetite and fever in young children may order further diagnostic tests.

A neurological examination generally finds that the patient is confused and drowsy.

If the neck is stiff, caused by irritation of the meninges, the doctor may consider meningitis or meningoncephalitis.

A lumbar puncture, which takes a sample of cerebrospinal fluid, may reveal higher-than-normal levels of protein and white blood cells (normal glucose). However, in some cases results may come back normal for patients with encephalitis.

A CT scan may be useful in detecting changes in brain structure. It can also rule out other symptoms causes, such as stroke, an aneurysm or a tumor.

An electroencephalograph may show sharp waves in one or both of the temporal lobes.

A blood test may be ordered if the doctor suspects the cause is a West Nile virus infection.

What is the treatment of encephalitis?

Treatment focuses on alleviating symptoms. There are only a limited number of reliably tested specific antiviral agents, such as acyclovir; success is limited for most infections except herpes simplex encephalitis.

Corticosteroids may be administered to bring down the brain inflammation, especially in cases of post-infectious (secondary) encephalitis.

If the patient has severe symptoms, he/she may need mechanical ventilation and other supportive treatment.

If patients have seizures they may be given anticonvulsants.

Sedatives may be effective for seizures, restlessness and irritability.

For patients with mild symptoms, the best treatment is rest, plenty of fluids, and Tylenol (paracetamol) for fever and/or headaches.

What are the complications of encephalitis?

The majority of patients who have encephalitis go on to have at least one complication, especially elderly patients, those who had symptoms of coma, and individuals who did not receive prompt treatment. Complications may include:

• loss of memory - especially among those who had herpes simplex virus encephalitis.
• behavioral and/or personality changes - such as mood swings, bouts of frustration and anger, and anxiety
• epilepsy
• aphasia - language and speech problems

How can encephalitis be prevented?

Vaccines - keeping up-to-date with vaccines is the most effective way of reducing the risk of developing encephalitis. These include vaccines for measles, mumps, rubella, and if the virus exists in those areas, Japanese encephalitis and tick-borne encephalitis.

In areas known to have mosquitoes that carry encephalitis causing viruses, take measures to reduce the risk of being bitten. This may include wearing appropriate clothing, avoiding mosquito-infested areas, avoiding going outside at specific times during the day when there are lots of mosquitoes about, keeping your home mosquito-free, using mosquito repellant, and making sure there is no stagnant water about your house.

Written by Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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