Electroencephalogram (EEG)

An EEG is the definitive test used to diagnose neurological disorders of the brain, such as seizures and epilepsy. The test is safe and painless. It measures electrical activity in the brain by recording brain waves. The test is performed by placing electrodes on the scalp in very precise locations. These electrodes do not deliver any electrical current and only record the electrical activity from your brain. The test is performed in a dimly lit, quiet room and the recording is continuous for 20 to 40 minutes. It takes approximately the same amount of time to set up, making the entire appointment 1 to 1 1/2 hours. During the test the EEG technologist may ask you to breathe deeply or rapidly, ask you to open and close your eyes, and or shine a light into your eyes. If you have any sensation or symptom of a seizure you need to tell the technician.
Many patients fall asleep during this test. This may even be helpful and result in acquiring additional useful data. Sometimes the doctor may request that you stay up the entire night before the EEG test is performed. Sleep deprivation can increase the likelihood of recording brain waves that indicate the diagnosis of epilepsy.

How to Prepare for Your EEG Wash your hair the night before or the day of the test and do not use any conditioners, hair creams, sprays, or styling gels.

Do not have more than 5 hours of sleep before the test.

What does a Normal EEG Mean? A normal EEG does not mean you are not having seizures or epileptic episodes. Unfortunately, approximately 1/2 of all EEGs performed on patients experiencing seizures are interpreted as normal. This is because an EEG records electrical brain activity and if you do not have a seizure it may or may not record the activity as normal. If you have a seizure the recording will definitely be abnormal. In some cases the test is just not long enough to catch the abnormal recording. In that instance and at the discretion of the neurologist or treating physician an Ambulatory EEG may be ordered.

Please note the findings of a normal EEG does not rule out the diagnoses of epilepsy or seizures. The neurologist also considers the patient's past medical history, MRI scan, physical examination and the patient's or observer's description of the events. The following are examples of information that would be important in confidently diagnosing seizures or epilepsy without a positive finding during an EEG; A past medical history of meningitis, head trauma, or a serious illness may make you more at risk for seizures; An MRI is relevant to determine abnormalities; The patient's or observer's description of an episode may indicate an anxiety or fainting spell instead of a seizure.

Important! Your normal EEG does not mean that the neurologist was wrong in saying that you had a seizure. Keep taking the seizure medicine that was prescribed. If you have a normal EEG and stay free of seizures for two years or more, the neurologist may suggest that you can stop taking it!