The EEG is the principal test for confirming a diagnosis of seizures and gathering information about their type and location. It can be performed in a neurologist’s office but sometimes patients are sent to a hospital to have the EEG performed in the neurology or epilepsy department sometimes called an Epilepsy Monitoring Unit (EMU). Whichever situation you are in, you may wonder whether your EEG will be of the same quality as an EEG performed in a different setting.
All else being equal, the location of the EEG equipment should not make any difference in itself. There are standard procedures for the placement of the EEG electrodes and for the way the test is performed and interpreted. Differences may arise, however, if one site has newer equipment or more experienced professionals to perform and interpret the test.
What are the advantages of the newest equipment?
You have probably seen pictures of basic EEG machines that draw the brain waves on long paper strips. New computerized (digital) EEG machines do not produce paper strips. Instead, they offer more options for viewing brain waves than the basic paper EEG machine.
One of the most important differences is that they allow the neurologist to look at more channels in searching for abnormal brain waves. The basic paper EEG machine provides from 8 to 21 channels, but many digital EEG machines offer 32 channels or even more. (Some have fewer than 32.) Viewing more channels increases the possibility of finding the "epilepsy waves" and helps confirm the diagnosis of either partial or generalized epilepsy.
Another advantage of the newer equipment is that with computerized recording, the neurologist can reformat the brain waves and view the same period of recording from a different perspective. With paper recording, such reformatting is not possible.
How important is the skill of the person interpreting my EEG?
EEG interpretation is an acquired skill. Neurologists with extensive experience in reading EEGs can provide more accurate interpretations than those with limited experience. Neurologists who specialize in reading EEGs (neurophysiologists) read hundreds of them during their training so they can become skilled at interpreting them.
They learn, for instance, to recognize the many things besides seizure activity that can alter an EEG recording. Opening the eyes, mental concentration, breathing fast, or looking at flickering lights all alter brain-wave patterns. If you move (by closing your mouth, for example), that creates changes in the EEG called artifact.
Experienced neurologists also learn to recognize the slight differences between what is normal for one patient versus what is normal for someone else. Subtle changes in brain waves may be interpreted as abnormal when the actual change is this kind of normal variant.
Interpreting EEGs also involves some subjectivity and judgment. (This is why the machine doesn't just spit out the interpretation along with the strip!) What one interpreter reads as sharp waves may be read as spikes by another. Both may be considered correct, depending on the criteria they apply. Experienced neurologists also learn to interpret the EEG in light of the patient's medical history, physical examination, and other laboratory studies.
What are other advantages of having my EEG performed in a hospital?
Epilepsy centers in hospitals generally use state-of-the-art equipment. The neurologists who work there have gone through special training in diagnosing and treating epilepsy. They may also have special qualifications in interpreting EEGs.
If your EEG is performed in a hospital or a large office practice, more than one neurologist may be able to review it. Such second opinions can decrease subjectivity and bias. Additional interpreters also can apply a wider range of experience to questions that may arise.
Even with the best technology and the most highly trained neurologists, however, your first EEG may turn out to be normal or inconclusive. You may need to have another EEG performed after sleep deprivation, or have ambulatory or video-EEG monitoring to record the epilepsy waves that are associated with your seizure activity.