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    Diagnosing Epilepsy: EEG's Limits - Topic Overview

    Electroencephalography (EEG) is thought to be the most useful test in confirming a diagnosis of epilepsy, but it is not foolproof.

    • Some people with abnormal EEG results do not have epilepsy. This is not common.
    • About 50% of people with epilepsy will have normal results on their first EEG.1 If epilepsy is still suspected, a follow-up EEG may be done. This second test may be a sleep-deprived EEG, in which the test is done after you have been forced to stay awake for a longer period of time than usual. A sleep-deprived EEG can sometimes reveal abnormalities that did not show up on the regular EEG.
    • From 10% to 40% of people with epilepsy will have normal EEG results even after having several EEG tests done.1

    Video and EEG monitoring records seizures on videotape and computer so that the doctor can see what happens just before, during, and right after a seizure occurs. The video records what you are doing while the EEG records the electrical activity occurring in your brain. This type of monitoring may be used:

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    Understanding Epilepsy -- Prevention

    In someone with epilepsy, certain triggers can lead to a seizure. Identify and watch for particular behaviors, environments, or physical and emotional signs that precede attacks. It's not uncommon, for example, to feel annoyed or elated several hours prior to a grand mal seizure, and immediately before the attack. In addition, the person may become aware of a warning "aura" -- perhaps a taste or smell: This warning may allow you to lie down in time to avoid falling. In cases where the aura is a...

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    • When your medical history and repeated EEGs are not enough to figure out what kinds of seizures you are having. Simultaneous video and EEG recording can provide important clues about what type of seizure you have had.
    • To evaluate your condition before you have epilepsy surgery.
    • To diagnose seizures that are not from epilepsy, such as psychogenic seizures.

    WebMD Medical Reference from Healthwise

    Last Updated: March 12, 2014
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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