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EEG - Results

Alternative Names

Electroencephalogram; Brain wave test

Normal Values:

Brain electrical activity has a certain number of waves per second (frequencies) that are normal for different levels of consciousness. For example, brain waves are faster when you are awake, and slower when you are sleeping.

There are also normal patterns to these waves. The EEG looks for these frequencies and patterns.

What abnormal results mean:

Abnormal results on an EEG test may be due to:

  • Abnormal bleeding (hemorrhage)
  • An abnormal structure in the brain (such as a brain tumor)
  • Attention problems
  • Tissue death due to a blockage in blood flow (cerebral infarction)
  • Drug or alcohol abuse
  • Head injury
  • Migraines (in some cases)
  • Seizure disorder (such as epilepsy or convulsions)
  • Sleep disorder (such as narcolepsy)
  • Swelling of the brain (encephalitis)

Note: A normal EEG does not mean that a seizure did not occur.

  • Reviewed last on: 1/4/2011
  • Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine. Also reviewed by Joseph V. Campellone, MD, Division of Neurology, Cooper University Hospital, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

References

Trescher WH, Lesser RP. The Epilepsies. In: Bradley WG, Daroff RB, Fenichel GM, Jankovic J, eds. Neurology in Clinical Practice. 5th ed. Philadelphia, Pa: Butterworth-Heinemann; 2008:chap 71.

Krumholz A, Wiebe S, Gronseth G, et al. Practice parameter: evaluating an apparent unprovoked first seizure in adults (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology and the American Epilepsy Society. Neurology. 2007;69(21):1991-2007.

Woo Lee J, Khoshbin S. Clinical neurophysiology and electroencephalography. In: Stern TA, Rosenbaum JF, Fava M, et al, eds. Massachusetts General Hospital Comprehensive Clinical Psychiatry. 1st ed. Philadelphia, Pa: Mosby Elsevier; 2008:chap 75.

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