The tests
Your neurologist may ask you to have some tests to get extra information about the seizures. The tests are usually done by a technician (a person who is trained to do them). The results from the tests are then passed back to the neurologist to see what they show. The results may indicate that you have epilepsy and may also say why you have epilepsy.
You may not need to have all of the tests mentioned in this leaflet, but the following information explains what the tests are, why they are done and what they might say about the seizures you are having.
Tests to rule out other causes
There are many different causes of seizures and some causes can easily be mistaken for epilepsy. Although seizures with different causes may look similar to epileptic seizures there are often subtle differences which help your doctor to make the correct diagnosis.There are a number of tests that can help
rule out other causes. These include the following tests:
Blood tests
To do a blood test, a sample of blood is taken, usually from your arm, with a syringe. The sample is used to check your general health. The test is also used to rule out other possible causes of the seizures, such as low blood sugar levels or diabetes.
Electrocardiogram (ECG)
An ECG is used to record the electrical activity of the heart. This is done by sticking electrodes (a bit like plasters) to the arms, legs and chest. These electrodes pick up the electrical signals from the heart.
Because an ECG does not give out electrical signals, having one doesn’t hurt. An ECG can help to rule out the seizure being caused by the way the heart is working.
Tests to diagnose epilepsy
No test can say for certain whether you do or do not have epilepsy. But when the information from the tests is added to the other information about what happens during the seizures, this builds up a clearer picture of what happened. This may help with the diagnosis and when choosing treatment.
Electroencephalograms (EEG)
An EEG is used to record the electrical activity of the brain by picking up the electrical signals from the brain cells. These signals are picked up by electrodes on the head and are recorded on paper or on a computer.
The recording shows how the brain is working. Like the ECG, the electrodes only record electrical activity - they do not give out electrical signals and they do not hurt.
Before the test, the technician places the small electrodes on your head – the electrodes are held in place with a sticky paste. The electrodes are connected to the recording machine. The test lasts about 30 minutes and you will probably be sitting or lying down.
What does an EEG show?
An EEG gives information about the electrical activity of the brain during the time the test is happening. When someone has an epileptic seizure their brain activity changes. This change can sometimes be seen on an EEG recording - it is often called epileptiform activity. Some people can have epileptiform activity even when they are not having a seizure, so an EEG can be particularly useful for them.
Epileptiform activity can sometimes be provoked by deep breathing. The test may include deep breathing to see if epileptiform activity can be provoked and recorded.
Your results
An EEG test can usually show if someone is having a seizure at the time of the test, but it can’t show what happens in the person’s brain at any other time. So even though your test results might not show any unusual activity it does not completely rule out having epilepsy. Some types of epilepsy are very difficult to identify with an EEG test.
Some people who do not have epilepsy can sometimes have irregular activity on their EEG. But a result where there is irregular activity does not necessarily mean that the person has epilepsy.
Flashing lights during the EEG
Some people with epilepsy have seizures that are started, or ‘triggered’, by flashing lights. This is called photosensitive epilepsy.
An EEG test will usually include testing for photosensitive epilepsy. You will be asked to look at a light which will flash at different speeds. If this causes any changes in your brain activity the technician can stop the flashing light before a seizure develops.
Sleep-deprived EEG
For some people there is more chance of irregular brain activity happening when they are tired or when they are going to sleep. If this is the case for you, having a sleepdeprived EEG might help get a more useful reading. This test is done in the same way as a normal EEG but you sleep during the test. To help you sleep, you may be asked to stay awake some, or all, of the night before. In some cases you may be given a mild sedative to help you get to sleep.
Ambulatory EEG
An ambulatory EEG works in the same way as a normal EEG but is portable. It is a small machine that is worn on a belt around your waist. Because it is portable you can move around and carry on with your normal day-to-day routine while the recording happens.
This type of EEG allows brain activity to be recorded for several hours, days or weeks. Because the brain activity is recorded for longer, there is more chance of a seizure being recorded on the EEG than during the normal 30 minute test.
Video telemetry
Video telemetry testing happens in hospital, usually over a couple of days. During your stay you have your own room. In the room, often mounted on the wall, there is a video camera that records what you are doing. At the same time you will wear a portable EEG so that you are able to move around your room. Being videoed whilst wearing an EEG means that if you have a seizure your doctor can compare the electrical activity of your brain with what is happening to your body.
The results can help identify what types of seizure you are having, and the most appropriate way of treating them.
Brain scans
Brain scans can be used to help find the cause of someone’s seizures. The scans produce pictures of the brain which might show a physical cause for epilepsy, such as scarring on the brain. But for many people a brain scan does not show up a cause for their seizures, and even if nothing unusual is seen, the person may still have epilepsy.
The two common types of brain scan are Magnetic Resonance Imaging and Computerised Axial Tomography.
Magnetic resonance imaging (MRI scan)
An MRI scan uses magnetic fields to take images of the brain. It can find scars, tumours or areas of damage to the brain, which may cause a person’s epilepsy.
Because an MRI scan uses strong magnetic fields, metal objects in or near the machine can affect, or be affected by, the machine. Before having an MRI scan you will need to remove any metal objects such as jewellery, hearing aids, coins or keys.
The magnetic fields mean that if you have a heart pacemaker or any surgical implant that contains metal you may not be able to have an MRI scan.
What happens during an MRI scan?
The scanner makes a loud noise so before it starts you will be given earplugs to wear. You will also be given a buzzer to hold - you can use the buzzer to let the technician know if you are feeling uncomfortable or unwell during the scan. The technician is usually on the other side of a window in another room during the scan, but an intercom means you can talk to them. There is also usually a mirror inside the scanner so you can see the technician during the scan. You may be able to have someone in the room with you during the scan.
During the scan you will lie on a platform which slides backwards into the scanner. When having an MRI scan to help diagnose epilepsy the scan usually takes about 30 minutes. Lying still during the scan is important so that the machine can take a clear image.
An MRI scan is usually a series of short scans with breaks in between rather than one long scan. Between each short scan the technician might use the intercom to check that you are comfortable.
Computerised axial tomography (CT or CAT scan)
CT scans use X-rays to take images of the brain. CT scans are not suitable if you are pregnant because of the X-rays. During a CT scan you lie on a couch which slides into the scanner.
Unlike MRI scanners, CT scanners do not make a loud noise. The pictures from a CT scan are often less detailed than from MRI scans.
© The National Society for Epilepsy
Information produced in July 2007
