Nerve cells communicate through tiny electrical signals. Electroencephalography, EEG for short, measures their sum via electrodes on the scalp and records it as traces. The device only records; it sends neither electricity nor radiation into the body.
During an epileptic seizure, nerve cells discharge excessively and simultaneously for a short time. This can show as jerking, stiffening and loss of consciousness, but also as a brief absence, a strange feeling or tingling. Not every seizure means epilepsy: lack of sleep, alcohol withdrawal, low blood sugar or an acute brain disorder can trigger a single seizure. Specialists speak of epilepsy when at least two seizures without such a trigger occur more than 24 hours apart, or when there is already a high risk of further seizures after a first one.
The EEG looks for patterns typical of epilepsy, which can also occur between seizures. They show whether seizures start in one area of the brain or involve the whole brain, and help to assess the risk of further seizures and the right treatment. However, a normal EEG does not rule out epilepsy. Repeated recordings, an EEG after sleep deprivation or a long-term recording make the findings more meaningful.
The EEG is one building block of the assessment, but not the only one. Just as important is an exact description of the seizure by people who witnessed it; a video on a mobile phone can be very helpful. In addition, there is magnetic resonance imaging (MRI) of the head, which according to the guideline should take place within a few days, as well as blood tests. This also makes it possible to distinguish epileptic seizures from fainting and other seizure-like events.