Encephalitis (inflammation of the brain)

Encephalitis is an inflammation of the brain that is most commonly caused by viruses. It may be mild or severe with long-term effects. A precise diagnosis is important for treatment.

At a glance

  • Encephalitis is the medical term for inflammation of the brain.
  • It is usually caused by viruses or by an auto-immune response in which the immune system attacks the body's own tissues.
  • Encephalitis impairs one or more functions of the brain.
  • Typical symptoms are impaired consciousness, confusion, epileptic seizures, fever, and headache. Changes in behavior and cognitive impairment are also common.
  • The condition may be mild or severe depending on the cause.
  • Targeted treatment is possible if the cause of the brain inflammation is identified.

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

A doctor examines a brain scan on a monitor.

What is encephalitis?

Encephalitis is an inflammation of the brain. If the brain inflammation occurs in conjunction with meningitis (infection of the meninges, i.e., the protective lining of the brain and spinal cord), this is known as meningoencephalitis.

Encephalitis is most commonly caused by a viral infection. Herpes simplex viruses are frequently responsible.

Auto-immune responses also play a role in the development of this condition. These are inappropriate responses of the immune system that cause damage to the body's own tissues.

Encephalitis may cause impaired consciousness, as well as changes to behavior and personality. Individual brain function may also fail and epileptic seizures may occur.

The condition can be mild but also may be life-threatening and cause severe, long‑term effects.

Important: If the encephalitis is caused by herpes simplex viruses, starting treatment is of critical importance. Early treatment reduces the risk of the condition being fatal.

What are the symptoms of encephalitis?

The most common symptoms of encephalitis are:

  • confusion
  • headache
  • seizures
  • impaired consciousness
  • fever

Changes in behavior, hallucinations and cognitive impairment are also common.

Different symptoms may occur depending on which virus is causing the inflammation:

  • Infection with herpes simplex viruses often causes speech disorders, such as aphasia.
  • Arboviruses, which are transmitted by insects, more commonly cause movement disorders.
  • An infection with enteroviruses typically causes shaking, muscle twitches, movement disorders, facial paralysis, and water in the lungs.

Other neurological symptoms may also occur, such as paralysis of one side of the body, flaccid paralysis of individual nerves, or numbness.

Sometimes, the disturbance of brain functions is so mild that it is barely noticeable.

Newborn babies and infants show symptoms of encephalitis that are of a more general nature – they don't drink well and are listless and lethargic. They may also experience fever and cramps.

What causes encephalitis?

Encephalitis can be caused by viruses, bacteria, fungi or parasites, such as single-cell organisms and worms. Such cases of encephalitis are known as infectious encephalitis.

Alternatively, encephalitis may be auto-immune encephalitis, in which the immune system develops antibodies that attack and damage the body's own cells in the brain. These antibodies are known as autoantibodies.

Causes of encephalitis: viruses, bacteria, fungi, parasites, autoantibodies.

Approximately 70 percent of cases of encephalitis are caused by viruses. The most commonly identified are as follows:

Encephalitis is sometimes caused by infections with measles, mumps and rubella viruses or, more rarely, by a SARS-CoV-2 infection.

Auto-immune encephalitis may occur as a result of cancer.

How common is encephalitis?

Every year, around 4 to 8 people in every 100,000 develop viral encephalitis. The condition affects young adults and older people in particular. Childhood encephalitis affects about 4 to 10 children in every 100,000 and occurs most commonly during the first year of life.

Every year, around 4 to 8 people in every 100,000 develop viral encephalitis.

There is also a seasonal variation in some types of viral encephalitis. Tick-borne encephalitis (TBE), which is widespread in Europe, occurs in early summer when ticks, which carry the disease, are especially active. The same applies to brain inflammations caused by pathogens that are spread by mosquitoes – such as West Nile virus.

What are the potential effects of encephalitis?

Many people with brain inflammation recover without any after-effects.

Long-term effects occur in around one third of cases. The most common of these are persistent seizures, impaired concentration, behavioral issues, and difficulties with memory or language. Often, these seizures cannot be treated effectively with medication.

Around one percent of people continue to suffer massive functional impairment of the brain after the inflammation has healed. These individuals never fully regain consciousness.

Around half of all children who develop encephalitis experience long-term limitations, such as developmental disorders, learning difficulties, or behavioral problems. Muscle movement, vision, hearing, or urination is sometimes impaired.

In viral encephalitis, progression of the condition depends to a large degree on the type of virus responsible. For example, there is a high risk of death from encephalitis caused by a herpes-simplex virus if it is not treated at an early stage.

How is encephalitis diagnosed?

Some brain inflammations are caused by pathogens that can be targeted directly with specific drugs.

For this reason, it’s important to pinpoint the precise cause. To narrow down the possibilities, doctors will ask the patient for information, for example, about:

  • their general health
  • any medication they require
  • prior vaccinations
  • recent travel

Symptoms such as skin rashes, swollen lymph nodes, memory and language impairments or certain movement disorders may point to a specific pathogen.

CT (computed tomography) or MRI scan (magnetic resonance imaging) can be used to scan sections of the brain to detect inflammation. The exact site of the inflammation in the brain may indicate its cause.

Doctors can also take a sample of liquor, i.e., cerebrospinal fluid, from the spinal canal in the spine if encephalitis is suspected. This is the fluid surrounding the brain and spinal cord. In the liquor, pathogens can be detected directly by means of genetic analysis or indirectly via the antibodies that target specific pathogens. Certain autoantibodies will be found in the liquor if the person has auto-immune encephalitis.

A blood sample may also help doctors to pinpoint certain antibodies produced in response to specific pathogens. 

An electroencephalogram (EEG) will be performed if the patient is having seizures.

How is encephalitis treated?

For many types of viral encephalitis, there is no specific treatment to target the precise cause. In these cases, treatment is limited to measures to relieve symptoms.

One exception is encephalitis caused by herpes simplex viruses. This type of brain inflammation can have severe consequences if left untreated. Long-term effects can be avoided if the medication aciclovir is administered at an early stage. For this reason, patients are usually given aciclovir even before the cause of their encephalitis has been identified.

Aciclovir and similar active agents are also used to treat brain inflammations caused by the varicella-zoster virus or cytomegalovirus.

Seizures are treated with antiseizure medication. Doctors may administer medication with an antipsychotic effect on a temporary basis if the person is having behavioral disturbances.

Non-viral encephalitis must be treated in accordance with its cause. If it is suspected that the encephalitis is bacterial, antibiotics are used at an early stage.

People with auto-immune encephalitis are given high-dose corticosteroids, which have an anti-inflammatory effect. Doctors also have the options of using blood plasma exchange (plasmapheresis) and drugs to weaken the immune system (immunosuppressives). These are aimed at preventing further damage by antibodies.

German Neurological Society (Deutsche Gesellschaft für Neurologie e.V. – DGN).

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