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Frequently Asked Questions

By Elaine Dowell, and reviewed by Alina Ellerington, The Encephalitis Society

 What is Encephalitis?

Encephalitis is an inflammation of the brain. 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).

 Who can get Encephalitis?

Anyone at any age can get Encephalitis.  There are up to 6,000 cases of Encephalitis in the UK and potentially hundreds of thousands worldwide each year.

 What causes Infectious Encephalitis?

Viruses are the most commonly identified cause of Infectious Encephalitis. Within the British Isles herpes simplex virus (HSV or the cold sore virus) is the virus most frequently identified. Worldwide other viruses are responsible, many of which are transmitted by mosquito. In some patients, the identity of the infecting virus is not conclusively determined despite extensive laboratory testing. More rarely bacteria, fungus and parasites can cause Encephalitis.

What causes Post-infectious Encephalitis / Autoimmune Encephalitis?

Autoimmune Encephalitis may be triggered by infection in which case the term “Post-infectious Encephalitis” is used.  ADEM (Acute Disseminated Encephalomyelitis) is a Post-infectious Encephalitis.  The illness usually follows in the wake of a mild viral infection (such as those that cause rashes in childhood) or immunisations.  Typically there is a delay of days to two to three weeks between the triggering infection and development of the Encephalitis.

Not all forms of Autoimmune Encephalitis are triggered by infection. Other forms of Autoimmune Encephalitis are associated with finding specific antibodies in blood. This group of causes of Encephalitis is called Antibody-Associated or Antibody-Mediated Encephalitis such as Voltage-gated Potassium Channel Complex Antibody-associated Limbic Encephalitis and N-Methyl-D-Aspartate-Receptor- associated Encephalitis.

What are the main symptoms?

Infectious Encephalitis frequently 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 long onset. Symptoms will vary depending on the cause but may include: confusion, altered personality or behaviour, psychosis, movement disorders, seizures, hallucinations, memory loss, or sleep disturbances.

How is Encephalitis diagnosed?

Diagnosis of Encephalitis is made when evidence of inflammation or swelling of the brain is identified. The range of possible symptoms and their rate of development vary widely, and are not just found in Encephalitis. Therefore making the diagnosis can be difficult. 

What tests are undertaken?

  • Lumbar Puncture (LP) - to detect inflammation, as well as the possible presence of infection, in the spinal fluid.
  • Brain scans such as Computerised Tomography (CT) or Magnetic Resonance Imaging (MRI) - to exclude brain tumours, aneurysms (a bulge in a blood vessel) and strokes and show the extent of any inflammation.  
  • Blood tests - to exclude metabolic encephalopathy (neurological disorders caused by systemic illnesses such as diabetes, renal failure, heart failure).

It is not unusual for the results of tests to be “normal”, however they are also important in excluding some other diseases. 

What is the treatment for Encephalitis?

Treatment of patients with Encephalitis has two aims. The first aim is to ensure that the patient receives specific treatment for the cause of their Encephalitis. Where the Encephalitis is thought to be caused either by a virus or bacteria, patients are treated with anti-viral and/or antibiotic drugs. Patients are frequently given several different drugs at once. It is important that these drugs are started promptly, and hence they will often be started before a definite cause is found. Acyclovir is the most frequently used anti-viral drug. It is effective against the Herpes Simplex and Varicella Zoster viruses. Unfortunately for many viral infections there are no specific treatments at present.

The second aim is to treat the complications arising from the Encephalitis and to support the patient whilst they are not able to perform their usual bodily functions. Often treatment with anti-convulsants to control seizures, or sedatives to reduce agitation is required.  Sometimes patients require Intensive Care treatment including ventilation (mechanical help with breathing).

Because Autoimmune Encephalitis is due to the immune system acting inappropriately, treatments aim to modify immune system function. These include drugs such as steroids (drugs to relieve inflammation), intravenous immunoglobulin (IVIG) (a blood product given into a vein in a drip) or plasma exchange (when some of a person’s blood is taken out from a vein, washed and then put back into the vein in a drip).

Do people get better?

Nerve cells may be damaged or destroyed by the viral infection, the immune reaction and by pressure resulting from the inflammation.  This damage is termed “Acquired Brain Injury (ABI).  Some loss of brain function is therefore a probable outcome of Encephalitis.  In some cases, however, this loss occurs on a relatively small scale resulting in very minor impairment, such as some loss in speed of thinking.  In other cases damage can be extensive leading to significant impairments.

Coming to terms with these problems can be potentially distressing and challenging for everyone concerned. The child or adult you knew, or who was you, may have changed and the child or person they have become, or you have become, may present with a number of problems. It is important to consider that it may take time for the individual and the whole family to adjust, in both practical and emotional terms, to their new situation

What are the after-effects of Encephalitis?

There will be a wide variation in how Encephalitis affects the person in the long term.  Tiredness, recurring headaches, difficulties with memory, concentration and balance, mood swings, aggression and clumsiness are often reported.  Epilepsy, as well as being a feature of the acute illness, may develop weeks or months after the illness has subsided.  Physical problems may include weakness down one side of the body, loss of sensations and of control of bodily functions and movement.  Speech and language problems may also be common features.  Speed of thought and reaction may be reduced.

Significant changes may occur in personality and in the ability to function day-to-day even if there is a complete physical recovery. 


Infectious types of Encephalitis tend to occur only once. It is rare for infectious types of Encephalitis to recur later in life. However, in the cases where there is worsening despite on-going treatment (Aciclovir), it may be due to insufficient doses (often based on the patient’s body weight) or other complications of Encephalitis may have developed, such as seizures. In unusual patients in whom there is a recurrence of Infectious Encephalitis early after stopping treatment (Aciclovir), it may be because the treatment was not given for a sufficient length

of time. In these cases, it is often appropriate to restart treatment promptly. Nevertheless, rarely in some patients, there may be an early recurrence of Encephalitis after stopping treatment that is due to inflammation even after the virus has cleared.

In some types of Autoimmune Encephalitis there is a recognised risk of recurrence. For example recurrence risk is in the order of 15% in patients with NMDAR-Antibody-Associated Encephalitis. It is difficult to accurately predict who will relapse but if the risk of relapse is considered to be significant, treatment is often offered over a longer period of time. Despite treatment a number of patients will still relapse. Recognition of potential relapses requires ongoing vigilance from the patient and their relatives and should be quickly reported to the patient’s neurologist. Relapses are more rarely seen in patients with LGI1-antibody Encephalitis.


Unfortunately, despite improvements in specific and more supportive treatments (i.e. intensive care management), Encephalitis still has a high mortality rate. When death happens it is usually because of severe brain inflammation. The rapid course of Encephalitis can be overwhelming. The realisation that today’s drugs, medical management and sophisticated equipment are sometimes unable to treat the disease successfully is frightening. Families who suffer a bereavement are often left feeling shocked and traumatised.

FS001V3 Questions and Answers

Page Created: March 2000/ Last Updated: August 2015/ Review date: August 2018

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 and references for 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.

The Encephalitis Society is the operating name of the Encephalitis Support Group which is a registered Charity and Company Limited by Guarantee.

Registered in England and Wales No. 4189027. Registered Office as above. Registered Charity No. 1087843.