It can be difficult to diagnose encephalitis. This is because the symptoms are similar to other conditions, such as meningitis.

Tests are needed to differentiate encephalitis from other brain conditions so treatment can be started as soon as possible.

Brain scans

CT scans or MRI scans can be used to highlight the extent of brain inflammation and help to distinguish encephalitis from other conditions, such as stroke, brain tumours and aneurysms (a swelling in the wall of an artery).

Lumbar puncture

A lumbar puncture, also known as a spinal tap, is used to test a sample of spinal cord fluid. The fluid, called cerebrospinal fluid (CSF), surrounds your brain and spinal cord and supports and protects them.

A hollow needle is inserted into the lower part of your spinal canal so that a sample of CSF can be drawn out for testing. During a lumbar puncture, local anaesthetic will be used so that you don't feel pain.

Electroencephalogram (EEG)

An electroencephalogram (EEG) is used to monitor your brain activity. During an EEG, small electrodes are placed on your scalp. These pick up the electrical signals from your brain and display them on a screen or piece of paper.

If you have encephalitis, an EEG may show abnormal brain activity.

Other tests

Screening blood, urine and other body fluids may also help confirm or rule out a diagnosis of encephalitis.

Screening can detect and identify infections of the brain or spinal cord. Results from these tests can also help to exclude conditions similar to encephalitis.