Routine EEG

EEG is an abbreviation used for electroencephalogram (a test that measures the electrical activity in the brain)

Technical aspects: During an EEG many electrodes are placed on the scalp to detect the electrical activity going on in the brain; this is then transmitted to a machine. This EEG machine produces graphs with waves representing the electrical activity of the brain. Different parts of the brain are being assessed since these electrodes are positioned across the scalp. A routine EEG could be done during an awake, drowsy and/or sleep state. It usually lasts between 20 to 60 minutes. On some occasions, provocative measures such as hyperventilation, photic stimulation (i.e. exposure to flashing lights) and sleep deprivation are used to bring on epilepsy activity.

Interpretation of results: In a patient without epilepsy, all the electrodes show balanced activity. In patients with epilepsy, some electrodes (partial epilepsy) or all (generalized) epilepsy show an excess of electrical activity which is called a “spike”.  The spike is a “marker” of epilepsy most of the time, but does not necessarily indicate that the patient is having a seizure at that particular time.

Important: not all patients with spikes on the EEG have epilepsy (about 2% of the population without epilepsy could show spikes, and will never develop seizures or epilepsy). Therefore, an “abnormal EEG” itself does not confirm the diagnosis of epilepsy. On the other hand, a patient with known epilepsy could have an EEG without spikes. Therefore, a “normal” EEG does not rule out epilepsy