This page covers the different types of EEG, referral and what happens during the different types of EEG testing.
Although electroencephalogram (EEG) testing can’t conclusively confirm or rule out a diagnosis of epilepsy, it can help doctors to identify patterns in brain activity.
You’ll also find information on the wearable brain-imaging system OPM-MEG, and video telemetry.
What is an electroencephalogram (EEG)?
An electroencephalogram (EEG) records electrical activity in the brain.
An EEG is a painless procedure that usually takes place in a hospital or clinic.
It can take as little time as an hour or may last several days.
Electrodes, about the size of shirt buttons, placed on the head send signals to a computer, which records them.
The EEG only gives information about electrical activity in the brain during the recording.
An EEG does not necessarily confirm a diagnosis of epilepsy because many people with epilepsy will have a normal result.
Nor can an EEG rule out a diagnosis of epilepsy.
But if the results do show where abnormal electrical activity is starting in the brain, this can help doctors to identify particular patterns.
This can then help them to identify a specific epilepsy syndrome and decide on the right treatment.
EEGs are most useful when used alongside video recordings so the doctor can see what’s going on in your child’s brain while observing how they’re behaving.
There are different types of EEG testing:
- Routine EEG
- Sleep EEG
- Ambulatory EEG
A routine EEG can be useful for anyone with a diagnosis, or suspected diagnosis, of epilepsy – child, young person or adult.
The procedure is carried out while the person is awake and lasts for 30–45 minutes.
During a routine EEG, other procedures are often performed to find out more about how the brain responds. These include:
- Hyperventilation – rapid, deep breathing
- Photic stimulation – watching a strobing light at different rates
- Exercise
- Sleep deprivation
- Reducing medication
The risks and benefits of hyperventilation, photic stimulation and sleep deprivation should be discussed first and only used if the child, young person, parents or carers, or adult agrees to their use.
If a routine EEG doesn’t provide enough information, it will normally be followed by a sleep EEG.
A sleep EEG is carried out while you're asleep during the day, using melatonin.
Sleep EEGs are very helpful for detecting seizures that happen when you’re sleeping.
Sometimes, you might be asked to stay awake the night before the test to help you sleep while the EEG is carried out. This is called a sleep-deprived EEG.
‘Ambulatory’ means being able to walk around.
In an ambulatory EEG, electrodes placed on the head are connected to a small recording unit carried in a bag around the waist.
During an ambulatory EEG, your child might go home for several hours or even days and carry on as normal.
Sometimes, the procedure can last for up to a week, but 24–48 hours is more usual.
At the end of the procedure, back at the hospital, the information is transferred onto a computer.
Sometimes, a portable video camera is also used during an ambulatory EEG.
Referral for an EEG
If a child, young person or adult has had a first seizure, and their medical history and assessment suggests it could have been an epileptic seizure, they may be referred for a routine EEG while awake.
Ideally, the routine EEG will take place within 72 hours after the first seizure. However, most of the time consultants won’t ask for an EEG until after a second seizure, and there’ll normally be a six-week wait.
If the results of the routine EEG are normal, then the next option is a sleep-deprived EEG.
If the results of the sleep-deprived EEG are also normal, the next option is referral for an ambulatory EEG for up to 48 hours.
Find out more about Young Epilepsy’s EEG diagnostic services.
Video telemetry
With video telemetry, your child stays in a special room where video monitoring takes place at the same time as the EEG recording.
This test usually involves at least an overnight stay in a hospital or specialist centre. It can take as much as a week but one to three days is more usual.
A parent or guardian must accompany the child having telemetry.
Video telemetry has two advantages over an ambulatory EEG:
- The child’s activities and movements are recorded at the same time as their brainwaves
- Other electrodes can be positioned elsewhere for a more detailed recording
The disadvantage of video telemetry is that having to spend most of the time in the same room can be quite tedious, especially for young children.
However, there is now a move towards doing video telemetry at home, if the NHS trust has the necessary equipment.
Find out more about Young Epilepsy’s video telemetry diagnostic services.
