Seizures: How does an electroencephalography (EEG) test help?
Understanding what is happening in the brain during a seizure can help diagnosis and correct management. One of the most important tools doctors use to investigate seizures is the Electroencephalography (EEG) test.
In this article, consultant clinical neurophysiologist and epileptologist Dr Elisaveta Sokolov explains what an EEG is, how it works, and how it helps doctors manage seizures.
What is an EEG?
An electroencephalography is a test that records the electrical activity of the brain. The brain communicates using tiny electrical signals, and an EEG detects these signals using small sensors, called electrodes, placed on the scalp. These electrodes pick up patterns of brain activity, which are then displayed as waves on a computer screen.
The test usually takes between 20 and 60 minutes, although in some cases longer monitoring may be required. Patients can usually go about their normal day after an EEG, as it does not involve radiation or invasive procedures.
Why is an EEG important for seizures?
EEGs are particularly valuable when doctors are investigating epilepsy. Here’s why:
Identifying abnormal brain activity
In epilepsy, the brain’s electrical activity becomes disrupted. An EEG can capture these disruptions, even if the person isn’t having a seizure at the time of the test. Certain patterns on an EEG may suggest a tendency to have seizures, helping doctors confirm a diagnosis of epilepsy.
Classifying the type of seizure
There are different types of epilepsy. Some start in one area of the brain (focal epilepsy), while others affect the whole brain (generalised epilepsy). EEGs help doctors understand these differences, which is essential for choosing the most effective treatment.
Guiding treatment decisions
EEGs also help in planning treatment. If abnormal activity is detected, doctors may adjust medications or recommend further investigations. In some cases, EEG results can help determine whether surgery or other therapies might be appropriate.
How to prepare for an EEG
Preparing for an EEG is straightforward:
- Wash your hair the night before, avoiding hair products.
- Get a good night’s sleep, unless your doctor instructs sleep deprivation to provoke brain activity, in which case follow their clear guidance.
- Continue medications unless advised otherwise by your doctor.
It is important to remain relaxed during the test, as movement can affect the results.
Understanding EEG results
EEG results are interpreted by specialist doctors such as clinical neurophysiologists or epileptologists. Abnormal patterns may suggest epilepsy or other neurological conditions. However, a normal EEG doesn’t always rule out epilepsy. Sometimes, repeated or longer-term EEG monitoring may be needed to capture infrequent epileptiform activity.
An EEG is a safe, non-invasive, and informative test that plays a key role in aiding the diagnosis and subsequent management of patients with epilepsy as well as excluding some non-epileptic pathologies in other patients.