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What is encephalitis?

Encephalitis is an inflammation of the brain. It is caused either by an infection invading the brain (infectious encephalitis) or through the immune system attacking the brain in error (post-infectious or autoimmune encephalitis).

Anyone at any age can get encephalitis. There are up to 6,000 cases in the UK each year and potentially hundreds of thousands worldwide. In the USA there were approximately 250,000 patients admitted to hospital with a diagnosis of encephalitis in the last decade.

Causes of encephalitis?

The inflammation is caused either by an infection invading the brain (infectious encephalitis) or through the immune system attacking the brain in error (post-infectious or autoimmune encephalitis). Viruses are the most frequently identified cause of infectious encephalitis (e.g. herpes viruses, enteroviruses, West Nile, Japanese encephalitis, La Crosse, St. Louis, Western equine, Eastern equine viruses and tick-borne viruses). Any virus has the potential to produce encephalitis, but not everybody who is infected with these viruses will develop encephalitis. Very rarely, bacteria, fungus or parasites can also cause encephalitis.

Some types of autoimmune encephalitis such as acute disseminated encephalomyelitis (ADEM) are caused by infection in which case the term ‘post-infectious encephalitis’ is used. Other forms of autoimmune encephalitis are associated with finding specific antibodies in blood such as VGKC complex (anti-LGI1 and Caspr2), NMDA receptor, GAD, AMPAR and GABA antibodies. Antibodies, also called immunoglobulins, are large Y-shaped proteins which identify and help remove foreign antigens such as viruses and bacteria. The reason why these antibodies are produced by the immune system in people with autoimmune encephalitis is not known in most cases. Sometimes a tumour (benign or cancerous) may generate the antibody.

Symptoms of encephalitis

Infectious encephalitis usually begins with a ‘flu-like illness’ or headache. Typically more serious symptoms follow hours to days, or sometimes weeks later. The most serious finding is an alteration in the level of consciousness. This can range from mild confusion or drowsiness, to loss of consciousness and coma. Other symptoms include a high temperature, seizures (fits), aversion to bright lights, inability to speak or control movement, sensory changes, neck stiffness or uncharacteristic behaviour.

Autoimmune encephalitis often has a longer onset. Symptoms will vary depending on the type of encephalitis related antibody but may include: confusion, altered personality or behaviour, psychosis, movement disorders, seizures, hallucinations, memory loss, or sleep disturbances.

Diagnosis of encephalitis

Symptoms alone often do not allow sufficient ability to distinguish between the many diseases that can mimic encephalitis. Therefore, doctors perform a variety of hospital tests such as spinal tap (lumbar puncture), brain scans (computerised tomography -CT or magnetic resonance imaging - MRI), electroencephalogram (EEG) and various blood tests. Sometimes, some of the tests cannot be taken immediately because of the patient’s medical state (e.g. patient is agitated). Nevertheless, it is important that investigations are carried out as soon as possible as prompt diagnosis reduces mortality and improves the outcomes.

For more information about the brain scan please read our factsheet on Neuroimaging

Treatment for encephalitis

Treatment of patients with encephalitis has two aims. Firstly, the patient will receive specific treatment for the cause of their encephalitis: antivirals for viral types of encephalitis (aciclovir for herpes simplex encephalitis); antibiotics for bacterial types and immunomodulatory drugs for autoimmune encephalitis (e.g. steroids, intravenous immunoglobulin, plasma exchange). For more information about the treatment in autoimmune encephalitis please download Immunotherapies in autoimmune encephalitis factsheet For some types of encephalitis there is no specific treatment aimed at the cause (e.g. West Nile encephalitis). Secondly, treatment is aimed at the symptoms and complications arising from encephalitis (e.g. seizures, agitation) and to support the patient whilst they are not able to perform their usual bodily functions (e.g. ventilation, insertion of a urinary or a feeding tube).

Some of the drugs (e.g. steroids) have potential side effects but also important benefits. In each patient the risk-benefit balance may vary, so the choice of treatment depends on each individual case. It is important that the treatment is started promptly, sometimes before a definite cause is found, as delay in treatment can be associated with unfavourable outcomes.

Sometimes a patient may be placed in an induced coma which is a temporary coma brought on by a controlled dose of drugs to shut down the brain and allow time to recover from the swelling caused by encephalitis. The doctors decide the length of the coma depending on the extent of injury and the way the patient reacts.

During and after the acute phase of encephalitis the patient may be uncharacteristically uncooperative, aggressive and even violent (acute confusional state). During this time, the patient is not aware of their behaviour or the impact it has on those around them or able to control it. When in this state, patients benefit from a ‘low stimulation’ environment. This means a quiet environment in which noise (e.g. from the television or telephone), and visits from others are minimised.

The after-effects of encephalitis

Nerve cells (neurons) may be damaged or destroyed and this damage is termed acquired brain injury (ABI). No two people affected will have the same outcome. Effects of encephalitis can be long-term. In children, injury to the parts of the brain that are not developed at the time of the illness can manifest later in life, well after the illness with encephalitis. Tiredness, recurring headaches, difficulties with memory, concentration, balance, mood swings, aggression, clumsiness, epilepsy, physical problems (weakness down one side of the body, loss of sensations and of control of bodily functions and movement), speech and language problems, reduced speed of thought and reaction, changes in personality and in the ability to function day-to-day, problems with senses and hormones are reported. The potential impact on social relationships should not be underestimated. Returning to work and school can be difficult.

Recovery and rehabilitation after encephalitis

The brain takes much longer to recover from an injury than other parts of the body such as muscles, bones and skin. Recovery can be a long and slow process and should not be rushed. The main aim of rehabilitation is to help the person affected by encephalitis develop new skills, habits and strategies for coping with their remaining difficulties. Depending on the nature of the person’s problems, rehabilitation may range from residential programs to home-based client services. The needs of each patient are unique and multiple. No two patients have the same outcomes. Input from various professionals, tailored to the individual needs is necessary (neuropsychologist, educational psychologist, occupational-therapist, speech and language therapist, physiotherapist, psychiatrist, dietician and/or nurses specialist).

Coming to terms with the problems left by encephalitis can be potentially distressing and challenging for everyone concerned. Unlike other parts of the brain, you cannot see the brain injury or repairing. People assume all is back to normal when in fact some areas are still in recovery. Encephalitis can be described as an invisible disability which affects not only one person, but the whole family. Emotional support for the whole family may be needed. 


What is encephalitis/ Version1, July 2017

Review date: July 2020

Disclaimer: We try to ensure that the information is easy to understand, accurate and up-to-date as possible. If you would like more information on the source material the author used to write this document please contact the Encephalitis Society. None of the authors of the above document has declared any conflict of interest which may arise from being named as an author of this document.