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

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 2 main types of scan used are:

• a CT scan 
• an MRI scan

A 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 may include:

• an electroencephalogram (EEG) – where 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