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Limitations of EEG in Diagnosing Epilepsy

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

Epilepsy Treatments: Find the Right Medication

Epilepsy is a brain disorder that causes repeated episodes of unprovoked seizures. There is no cure for epilepsy, but medications may help keep symptoms under control. Epilepsy is almost always treated first with medication. Choosing the right one, however, can be challenging. There are at least 20 different drugs available to prevent seizures. Some have been around for decades. Many others have only been developed recently, and each drug comes with its own benefits and risks. Also, side effects...

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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.

Citations

  1. Bazil CW, Pedley TA (2010). Epilepsy. In LP Rowland, TA Pedley, eds., Merritt?s Neurology, 12th ed., pp. 927-948. Philadelphia: Lippincott Williams and Wilkins.

By Healthwise Staff
Primary Medical Reviewer Susan C. Kim, MD - Pediatrics
Specialist Medical Reviewer Steven C. Schachter, MD - Neurology
Last Revised August 26, 2011

WebMD Medical Reference from Healthwise

Last Updated: August 26, 2011
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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