Diagnosing encephalitis 

Diagnosing encephalitis can be difficult because the symptoms are similar to those of other conditions, such as meningitis.

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

In the UK, encephalitis is a notifiable disease, which means that if a doctor diagnoses the condition they must notify their local authority.

Brain scans

CT scans or MRI scans can be used to identify 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, supporting and protecting 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. Local anaesthetic will be used so that you don't feel any pain.

Electroencephalogram (EEG)

An electroencephalogram (EEG) is used to monitor your brain activity. Small electrodes are placed on your scalp, which 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 bodily fluids may also help to confirm or rule out encephalitis.

Screening can detect and identify brain or spinal cord infections. Results from these tests can also be used to help exclude conditions that are similar to encephalitis. 

Page last reviewed: 16/12/2014

Next review due: 16/12/2016