Seizure? How can an electroencephalography test help

Seizures are episodes of convulsions or blankness that are often the sign of neurological dysfunction. In this article, a consultant clinical neurophysiologist explains how electroencephalography tests can uncover the cause of seizures.

 

 

What is a seizure?

A seizure is a spike of electrical activity in the brain that can disrupt function. An individual undergoing a seizure may exhibit signs such as:

• Involuntary trembling and jerking
• Heavy breathing
• Foaming at the mouth or grinding their teeth
• Falling to the floor and a loss of consciousness
• Not responding to their name or external stimuli
• Vomiting and a loss of the bowels

There are different kinds of seizures, so the signs of a seizure may be more subtle, such as repetitive movements like swallowing again and again, and experiencing unusual smells and tastes.

Sometimes seizures can come on suddenly, especially for those who are experiencing them for the first time, but sometimes there are warning signs that precede a seizure, like migraines, nausea, and dizziness. Some patients have seizures that are triggered by certain things, like a lack of sleep, flashing lights, and even menstruation.

Seizures can have many contributing factors. They can be a familial trait passed down through the generations, caused by brain tumours, strokes, head trauma, or cerebral infection.

 

How are the causes of seizures diagnosed?

An electroencephalogram (EEG) is one of the baseline tests to conduct on a patient experiencing seizures. An EEG records the electrical brain activity via 20 or so electrodes that are placed on the scalp, and the data is sent to a computer which records and displays the activity in the form of waves. A neurologist or neurophysiologist can then analyse and interpret the brain activity for anything unusual. An EEG can pinpoint where exactly abnormal activity is occurring in the brain, which can help differentiate between the kinds of seizures the patient is experiencing. The test involves the patient lying or sitting down, and it will take around 20-40 minutes. One kind of EEG, the sleep EEG, is conducted while the patient is resting or asleep, as brain activity in wakefulness is different as compared to when asleep. Results from an EEG can take a week or so to process and be shared with the patient.

EEG tests are recommended for patients who are suspected to have epilepsy, which is a disorder characterised by repeated seizures, or for patients already diagnosed with epilepsy but their doctors want to know more about their condition and their response to medications and therapy.

 

What are the limitations of an electroencephalogram?

However, the EEG can only show the current brain activity, so unless a seizure happens during observation or the brain activity of the patient is abnormal even outside of a seizure, a patient may need to come back for further testing, or their doctor may try to trigger a seizure by asking the patient to not sleep the night before (sleep deprived EEG) or synchronising the appointment with the patient’s menstrual cycle, or the patient may be given a smaller, portable version of an EEG machine and asked to wear the electrodes for a day or so to record the brain activity throughout the day and hopefully catch a seizure to record (ambulatory EEG). An EEG also cannot show structural issues, so if it is thought to be caused by a growth or physical damage to the brain tissue, the patient will be recommended to undergo an MRI or a CAT scan as well.

Depending on the recorded electrical activity, this can help doctors uncover the exact cause to the seizures and they will be able to progress to the next step: devising a treatment plan for the patient.