There is no single test that can diagnose epilepsy, making it difficult to get a diagnosis. Yet early and accurate diagnosis is essential to ensure patients are put on appropriate treatment pathways.
Epilepsy is usually diagnosed following at least two seizures occurring more than 24 hours apart. A GP makes a referral to a specialist neurologist who will take the patient’s medical history, and conduct a range of investigations before making a formal diagnosis. Tests on their own are not usually enough to make a diagnosis of epilepsy.
An EGG measures the brain’s electrical activity via electrodes placed on the scalp. The recording shows how the brain is working and provides insights into the brain’s functioning, allowing clinicians and researchers to study different brain states, such as wakefulness, sleep and various stages of sleep.
‘Brain trace showing epileptic activity’
An EEG is non-invasive, takes place in hospital and is pain free. However, an EGG is often normal in people diagnosed later with epilepsy, so methods such as flashing lights, or sleep deprivation are sometimes used to try to deliberately provoke abnormal electrical activity in the EEG. This is because an EEG can show if you’re having a seizure at the time of the test, but it can’t show what happens to your brain at other times.
An MRI uses magnetic fields and radio waves to penetrate the brain to give detailed scans which will show small lesions and scars on the brain. MRI’s are useful in identifying the location of the seizure activity, so are typically used when surgery is being considered.
Occasionally it may be necessary to inject a dye into the veins to enhance the images. This investigation is non-invasive, painless and should take about an hour.
In 2019, we awarded a grant to Dr Umesh Vivekananda from the Institute of Neurology, UCL to develop a state of the art form of electrical brain recording called portable Magnetoencephalography [link to study].
These use X-rays of the brain to provide cross-section images of the brain that are stored on a computer. Like with MRI scans, sometimes a dye is injected into a vein to improve the images. While the scan itself will only take around 10 minutes, it takes up to 60 minutes preparation time. Images from a CT scan are less detailed than those from MRI scans.
This procedure requires a person suspected of having epilepsy to wear a tape cassette recorder to monitor and record electrical activity in the brain over an extended period of time. This type of EGG shows brain activity while the person is awake and asleep.
This combines EEG monitoring with simultaneous video recording of the seizures. It’s usually carried out over a few days and is mainly used when the diagnosis is unclear or for assessment for surgery.
A PET scan is usually performed between seizures. The scan produces a 3D image of the brain and uses a tracer to observe and analyse brain function.
Single photon emission computerised tomography (SPECT) scan
This technique is similar to the PET scan where the most common tracer used measures the blood flow in the brain. The injection of the dye will typically be done during seizure activity, when video-EEG telemetry is taking place. The scan, which takes about 20 minutes, highlights ‘hot spots’ of seizure activity. It’s typically used when people are being assessed for epilepsy surgery.
Find out more about the diagnosis of epilepsy in this Research Roundtable webinar