Skip to content

Epilepsy Health Center

Font Size

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 Epilepsy -- Diagnosis and Treatment

To diagnose epilepsy, your doctor will take a detailed medical history (including a family history of seizures), gather information about your behavior before, during, and after the episode, and do a physical exam. Make sure someone who witnessed the seizure goes to the doctor with you.   An electroencephalogram (EEG) -- a brain wave study -- can reveal abnormal brain waves characteristic of epilepsy and sleep deprivation. Keeping someone awake for 24 hours increases the chances of finding abnormalities...

Read the Understanding Epilepsy -- Diagnosis and Treatment 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.

    This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http:// cancer .gov or call 1-800-4-CANCER.

    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.
    1
    Next Article:

    Diagnosing Epilepsy: EEG's Limits Topics

    Today on WebMD

    human head and brain waves
    Causes, symptoms, and treatments.
    Grand mal seizure
    How is each one different?
     
    marijuana plant
    CBD, a plant chemical, may cut down seizures.
    prescription bottle
    Which medication is right for you?
     
    Seizures Driving
    Article
    Questions for Doctor Epilepsy
    Article
     
    Graces Magic Diet
    Article
    Pills spilling from bottle in front of clock
    Article
     
    first aid kit
    Article
    Caring Child Epilepsy
    Article
     
    Making Home Safe
    Article
    epilepsy monitoring
    Article
     

    WebMD Special Sections