Tests and procedures

Electroencephalogram (EEG)

Used to help diagnose epilepsy by recording the electrical activity in the brain. The EEG is a non-invasive procedure that means it does not cut the skin or enter any internal space of the body. It is a very safe and pain-free test.

There are several different types of EEG tests that may be required to detect seizures and diagnose the specific type of epilepsy a person may have. The different types of EEG are described below.

Routine EEG

A routine EEG uses small recording contacts (i.e., ‘electrodes’) that are placed onto the scalp with paste. It is these contacts that detect and record the electrical activity in the brain. This information is then transferred to a computer and later interpreted by a scientist and a neurologist. During the test, the patient will be asked to lie still for 20 minutes while the brain activity is recorded. The patient may also be asked to breathe deeply for 3 minutes and/or may be shown a flashing light. The whole procedure takes about 60 minutes after including placement of the recording contacts, recording and removal of the contacts.

Sleep deprived EEG

A sleep deprived EEG is very similar to a routine EEG except that patient is asked to stay awake for the previous night before the test. The reason for this is that some of the changes associated with epilepsy are more easily observed when sleep deprived. The patient will attend for the EEG that will be carried out in the same way as the routine EEG described above. A period of sleep is usually achieved during which time the brain activity is recorded.

Ambulatory EEG

An ambulatory EEG is considered a longer-term recording. The small EEG recording contacts are attached to the scalp using a medical adhesive and the patient is sent home with a small recording device. Brain activity is continually monitored until the next day. During this time the patient is asked to record any typical events on a diary sheet at home and in some cases to press a button when they experience their typical symptoms. The next day the patient returns to RBWH to have the recording contacts and device removed.

Video EEG Monitoring Admission

Video EEG monitoring is another type of long-term recording however it requires patients to be admitted to hospital for up to two weeks in a private room with bathroom facilities. The aim is to record a number of typical seizures on EEG and at the same time video record what happens during a seizure. This helps the treating neurologists to better understand the type/s of seizures that may be occurring and in some cases to locate where in the brain the seizures begin. Sometimes during this admission other tests are also performed (e.g., SPECT).

As with other types of EEG, the video-EEG monitoring requires that recording contacts be attached to the scalp using a medical adhesive. The video-EEG monitoring admission is a big commitment as patients are unable to leave the bed (except for bathroom visits) for the period of monitoring. Before the video EEG admission is booked all patients will receive some additional information from the Epilepsy Nursing team regarding this investigation.

Invasive EEG Monitoring

These advanced tests may be considered in the context of an ongoing evaluation for epilepsy surgery. They aim clarify the exact location where the seizures begin in the brain. This is a major surgical procedure where electrodes are placed on or within the brain. After placement of the electrodes a further period of video-EEG monitoring will then be required. If this investigation is required, the patients treating doctors will discuss the procedure at length. The patient will be able to ask any questions and take time to decide if they wish to proceed.

Imaging Used to Diagnose Epilepsy

MRI (Magnetic Resonance Imaging)

An MRI scan uses a magnetic field and radio waves to provide detailed images of the brain. It allows identification of changes in the structure of the brain that are known to cause epilepsy. No radiation is used. The patient lies in a tunnel while the scan takes place. The machine can make loud tapping noises. There will be mirrors to see outside of the MRI and music to help the patient relax. The patient can communicate with the technicians through an intercom. The scan takes 30 to 60 minutes.

fMRI (Functional Magnetic Resonance Imaging)

An fMRI scan helps to identify the areas of the brain that are responsible for certain functions. This scan is like a standard MRI except that the patient will be asked to perform some tasks to activate specific brain functions during the scan. For example, to locate language areas you may be asked to think of words or finish incomplete sentences while the scan is happening. The scan takes approximately 30 to 60 minutes.

PET (Positron Emission Tomography)

This scan looks at how glucose is used in the brain and can help to locate which parts of the brain seizures begin from. The patient is asked to fast beforehand.  A small dose of a radioactive substance is injected for the test.  An EEG is performed on the patient for about 30 minutes before and some time after the injection to make sure no seizure activity is occurring as the time of the test, as this can affect the results. . The isotope is taken up by the brain over 60 minutes and then the scan is performed, taking about 30 minutes.

SPECT (Single Photon Emission Computerized Tomography)

This test usually occurs in an inpatient video EEG monitoring admission for surgical evaluation. A SPECT scan looks at blood flow in the brain and used the fact that during a seizure the blood flow to the seizure origin is increased. A radioactive substance is injected into the blood stream at the time of a seizure and carried to the brain allowing a scan to be done in the next few hours to help locate where the seizure began from. Usually a follow up scan, when the patient has not had a recent seizure, is also required. Each scan takes 30 minutes.

Neuropsychological Testing

A neuropsychological assessment involves doing tests that are sensitive to changes in brain functioning. Unlike the MRI scan which looks at the structure of the brain (i.e., how the brain looks), the neuropsychological assessment looks at how well the brain is performing on different types of thinking tasks (i.e., how the brain is functioning).

The neuropsychologist will take each patient referred for this test through a detailed interview and then a series of assessment tasks that look at a range of thinking skills; for example, memory, attention, planning, organisation and language, as examples. This assessment helps to identify any areas of strength or weakness and may even be helpful in locating which regions of the brain have been affected by seizures. Testing may take between 4-6 hours to complete though breaks can be taken as often as required. There is no pass or fail on this test; instead it provides a snapshot of current strengths and weaknesses.

Visual Field Testing

This is a type of eye test that maps the patient’s normal field of vision. It specifically measures how much vision the patient has in the peripheral field of their vision.  This can be affected by brain lesion pre and post surgery. It is done by asking the patient to respond to visual stimuli brought into their visual field and mapping the result. It is used to predict and evaluate the effects of brain surgery.