An electroencephalogram (EEG) records brain waves detected by electrodes placed on the scalp. This is the most common diagnostic test for epilepsy, and can detect abnormalities in the brain's electrical activity. People with epilepsy frequently have changes in their normal pattern of brain waves, even when they are not experiencing a seizure. While this type of test can be very useful in diagnosing epilepsy, it is not foolproof. Some people continue to show normal brain wave patterns even after they have experienced a seizure. In other cases, the unusual brain waves are generated deep in the brain where the EEG is unable to detect them. Many people who do not have epilepsy also show some unusual brain activity on an EEG. Whenever possible, an EEG should be performed within twenty-four hours of a patient's first seizure. Ideally, EEGs should be performed while the patient is sleeping as well as when he or she is awake, because brain activity during sleep is often quite different than at other times.
Video monitoring is often used in conjunction with EEG to determine the nature of a person's seizures. It also can be used in some cases to rule out other disorders such as cardiac arrhythmia or narcolepsy that may look like epilepsy.
EEG's at Penn State Hershey
Please arrive fifteen minutes early for your appointment. Please come with clean hair - no hairspray, gel, or mousse. Please be sure to have eaten within two hours prior to your study.
Your procedure should last approximately 1 hour. During your study, you will be asked to perform some deep breathing exercises, look at some flashing lights, and answer some questions.
All appointments are located in the Neurophysiology Lab: 30 Hope Drive, entrance B, Suite 1400 but accessed through Suite 1300 - Neurology. The Neurophysiology Lab telephone number is 717-531-8697.
When the initial EEG does not show abnormalities, a repeat EEG performed after sleep deprivation may be abnormal. Patients are asked to restrict the amount they sleep the night before they have their EEG and come to the lab in the morning. They do not have to stay up all night, as partial sleep deprivation (restricting sleep to approximately half the usual hours) is also effective. It is important for patients to avoid driving themselves, but rather to have somebody else drive when they come for the EEG after sleep deprivation.
Routine EEGs, which are usually thirty minutes in length, identify abnormalities in only 70-85% of patients, even with sleep deprivation and repeated studies, so that some patients with spells will not have EEG abnormalities to support a clinical diagnosis of epilepsy. This has resulted in the need for EEG studies that allow brain activity to be studied for longer periods.
Ambulatory EEG monitoring involves prolonged (usually 24, 48, or rarely 72 hours) outpatient recording of EEG in the patient’s home or work environment. The extended time frame increases the likelihood of recording abnormalities, and may also allow recording of the events themselves, so that EEG changes during the events can be studied. Patients cannot wash their hair as long as the electrodes are attached, but can perform all other activities.
Procedure at Penn State Hershey:
All patients report to the Outpatient EEG Lab at the East Campus facility on the scheduled day for attachment of EEG electrodes. They go home with the electrodes and a portable recording unit. Patients are provided a diary where they are asked to record all their activities, including their events, during the recording so that any changes noted on the EEG can be correlated to these activities. They return to the EEG Lab after 24 or 48 hours to have the electrodes removed. A physician later reviews the entire record and provides a written report.