Diagnosis of Encephalitis

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Encephalitis is diagnosed once other conditions, such as brain tumour, stroke or rapid onset Multiple Sclerosis (MS) have been ruled out, using the results of a lumbar puncture and any scans that are performed.

The spinal fluid is examined for evidence of infection. An analysis of the fluid in the spine (cerebrospinal fluid) is also known as a spinal tap or lumbar puncture.

A needle is inserted in your lower back between the bones of the spine. The doctor can tell if there is a bacterial infection because there will be an increase in the number of white blood cells in the fluid. If the fluid is â€˜clearâ€™ this will exclude bacterial meningitis. The fluid will also be tested for viral particles, in particular the herpes simplex virus.

You may also have a CT and/or MRI scan, which may show up areas of brain swelling and fluid content (oedema). These scans may show whether you have encephalitis or if the cause is something else. For example, a tumour or a stroke.

An electroencephalogram (EEG) can also help confirm a diagnosis of encephalitis by recording any unusual patterns of electrical activity in the brain. If this is the case, then the EEG may show an abnormal increase or decrease in electrical activity.

Blood tests are taken to exclude non-viral causes of encephalitis such as metabolic encephalopathy.

Encephalitis is a statutory notifiable disease so the doctor who makes the diagnosis is responsible for reporting it to the local Public Health department.