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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:

    Recommended Related to Epilepsy

    Understanding Seizures -- the Basics

    A seizure occurs when there’s abnormal electrical activity in the brain. Seizures may go virtually unnoticed. Or, in severe cases, they may produce a change or loss of consciousness and involuntary muscle spasms called convulsions. Seizures usually come on suddenly and vary in duration and severity. A seizure may be a one-time event, or you may have seizures repeatedly. Recurrent seizures are called epilepsy, or a seizure disorder. Less than one in 10 people who has a seizure develops epilepsy. Experts...

    Read the Understanding Seizures -- the Basics article > >

    • 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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