Encephalitis : Diagnosis

The symptoms of encephalitis can have a number of possible causes, so several tests may be needed to diagnose it.

The main tests used are outlined below.

Brain scans

A scan of the brain can help show whether you have encephalitis or another problem such as a stroke, brain tumour or brain aneurysm (a swelling in an artery).

The two main types of scan used are:

  • a CT scan – several X-rays are taken from different angles and are put together by a computer to create a detailed image of the brain
  • an MRI scan – strong magnetic fields and radio waves are used to produce a detailed image of the brain

Lumbar puncture

lumbar puncture is a procedure to remove some fluid from around the spinal cord (the nerves running up the spine) so it can be checked for signs of encephalitis.

For the procedure:

  • you lie on one side and bring your knees up towards your chin
  • local anaesthetic is used to numb your lower back
  • a needle is inserted into the lower part of your spine and a sample of fluid is removed

The sample will be checked for signs of infection or a problem with your immune system, which are the main causes of encephalitis.

Other tests

Several other tests may also be needed to help diagnose encephalitis and check for an underlying cause.

These may include:

  • an electroencephalogram (EEG) – small electrodes are placed on your scalp, which pick up the electrical signals from your brain and show abnormal brain activity
  • tests of your blood, urine or other bodily fluids to check for an infection
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