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Two other common uses for EEG testing are for assessment of confusional states and sleeping disorders.
In people with confusion or memory loss, an EEG can show different patterns depending on
cause. When confusion is caused by a depressed mood, EEG remains normal. When confusion is caused by a degenerative dementia like Alzheimer's disease or by a metabolic condition like a drug-overdose, brain's rhythms become slower.
For evaluation of sleeping problems, an EEG is just one component of a battery of recording systems. Through concurrent monitoring of other biological processes—like breathing, blood-oxygenation, heartbeat, muscle activity and eye movements—conditions such as narcolepsy and obstructive sleep apnea can be diagnosed.
So what can you expect if your doctor refers you for an EEG study? In many cases, you won't need to make any special preparations for test, but in cases where epilepsy is under consideration, you might be asked to stay awake for much of preceding night. Sleep-deprivation increases likelihood of recording a seizure-related abnormality in patients who have them. You are usually allowed to eat before test.
The testing-session lasts about two hours, though can be longer, especially if a sleeping problem is being evaluated. The EEG technologist uses much of testing-session to attach about two dozen metal-disk electrodes to scalp in standardized locations, and then to test electrical characteristics of each electrode to ensure that good connections have been made.
Once electrodes are in place recording session can begin. For most of recording you lie quietly with your eyes closed. The technologist measures brain-waves during quiet wakefulness, and then if you fall asleep, that is recorded, too. In additional parts of test, you might be asked to breathe rapidly and deeply for about three minutes (useful in detecting "absence" or "petit mal" epilepsy) or to watch flashing lights (useful in detecting certain other kinds of epilepsy). Then electrodes are disconnected and you go home.
A physician subsequently reads recording and makes a report. The report includes a description of observed rhythms of brain-waves, details of any detected abnormalities and comments about their possible significance. Your own doctor uses this report along with what else is known about your condition to make a diagnosis.
If you need an EEG, good news is that test is not painful. No needles are involved. There is no need to shave or otherwise remove hair. The bad news is that adhesive used to attach electrodes to your scalp can take a day or two to scrub out, and might require mineral oil to remove. Beauty-shop treatments should be postponed until after EEG appointment; hair-dresser's efforts will be ruined if EEG comes second. (C) 2005 by Gary Cordingley
Gary Cordingley, MD, PhD, is a clinical neurologist, teacher and researcher who works in Athens, Ohio. For more health-related articles see his website at: http://www.cordingleyneurology.com
