Diagnosing Epilepsy: Understanding the EEG
Video duration 9:04 | Read the transcript
When Maya was five years old, her parents, Jay and Clemencia, noticed that she was experiencing quick jerks in her upper body. Because Jay and Clemencia weren't always present when the movements happened, it had taken them about three or four months to actually recognize that something might be abnormal. They described the behavior to Maya's pediatrician, who recommended that Maya have an electroencephalogram, or EEG.
The EEG is a test that has been used since the 1930s to measure the brain's electrical activity. One of the ways the brain works is by generating electrical currents, which are similar to the electrical currents that produce light but in much smaller amounts. If a child exhibits any unusual and repetitive behaviors that could be consistent with seizures, such as staring in school, jerking of the limbs, walking unsteadily, or slurring their speech, doctors recommend that the child undergo an EEG to look for abnormal electrical activity in the brain.
Because doctors hope that children will sleep for a portion of the test, parents are often asked to bring their child in for the EEG in a sleep-deprived state. The night before her EEG, Maya stayed up until after midnight watching a movie with her parents, and was also awakened early the next morning so that she would still be sleepy. Before leaving for the hospital, Maya selected a special outfit and chose a favorite doll to bring along for comfort.
Once at the hospital, 20 electrodes were affixed to Maya's scalp using a removable adhesive gel. Her head was measured and the electrodes were placed at regular intervals so that the electrical activity in her brain could be measured in all four lobes of the cerebrum. Placement of the electrodes can be the most time-consuming part of the test, taking up to about an hour.
Even though the EEG is noninvasive and completely harmless, the experience of being in a hospital and having electrode wires attached to the head may be frightening for some children. For others, especially very young children or those with attention issues or cognitive impairment, it may be difficult to sit still through the preparation time and the test. Some parents may feel frightened themselves, but typically after families go through the experience once, the procedure becomes less intimidating.
Clemencia comments, "The EEG to me was something that I never heard about, and it felt to me like a very invasive procedure, so I had many doubts. I even called some friends of ours who are doctors, and I asked them if we should go through this thing, as I thought Maya could be traumatized by this test. So the first experience was a little scary—I was very nervous seeing Maya going through this procedure—but the second EEG went through easier and we took it much better."
During the EEG, brain activity is sampled while the child is awake, drowsy, and asleep. The EEG technologist also performs activating procedures like deep breathing, or hyperventilation, and photic stimulation during which a strobe light is flashed at various frequencies while the child opens and closes his or her eyes. These procedures are done to provoke abnormal brain wave activity and may help doctors determine if a child is at risk for having seizures. Because the standard EEG test takes only about 20 minutes, it is quite unusual for a child to have an actual seizure during the procedure, and doctors don't expect to record one. But even without capturing a seizure, doctors may still be able to analyze the EEG and detect abnormal interictal signals, allowing them to make a diagnosis.
In analyzing an EEG, doctors are looking for any abnormal brain wave activity that may be suggestive of seizures. Doctors pay close attention to amplitude, or voltage of brain waves, as well as the current, or duration of the waves. They look for deviations from normal brain waves called sharp waves, spike waves, and slow waves. What distinguishes sharp and spike waves from normal brain wave activity is that they are more sharply contoured waveforms that vary in amplitude. Each sharp wave has a duration of 70 to 200 milliseconds. Spike waves are shorter current lasting less than 70 milliseconds. Slow waves are much slower frequency than normal brain waves and can also vary in amplitude. Spike waves, sharp waves, or distinct patterns of spike and sharp waves or spike and slow waves may be indicative of seizure activity. Additionally, slowing of brain waves may suggest a structural or functional abnormality, such as a tumor or an area of the brain that developed abnormally, that could be associated with seizures.
Epileptologist Elizabeth Thiele, MD, PhD, continues, "What we're looking for are patterns of abnormal electrical activity that might help us say, Yes, this is a seizure the child is having, might help us to say where in the brain the seizures are coming from, and might help us decide what would be the best medication to start the child on to treat the seizures."
After the test was completed, Maya's EEG results were sent to her neurologist for analysis and she was diagnosed with generalized epilepsy. The abnormal brain wave patterns indicated myoclonic seizures, which are consistent with the quick jerks Maya had been experiencing. (To learn more about seizure types, see the Seizure Types and Syndromes section.)
Maya was started on a series of medications known to be effective with generalized epilepsy, but unfortunately the first few medications failed to control her seizures. After a few trials of different medications and combinations of medications, as well as adjustments to the dosages, her seizures have been brought under complete control.
After Maya is seizure free for a period of time, typically one year, she will undergo another EEG. If the EEG shows any abnormality, or irritability in her brain, the medications will be continued. If the EEG is normal, showing that the abnormality has quieted down, her doctor will begin to taper off her medications one at a time. The chances are good that Maya will eventually be able to come off all of her medications and remain seizure free. With generalized epilepsies, doctors expect most children to outgrow their seizures at some point during childhood.
Clemencia comments, "Of course we hope that she can one day be seizure free and have a life without medication. But now we are very happy knowing that the medicines are working out because it took us two years to find the right balance of medications."
To learn more about diagnosing epilepsy, see the Diagnosis section.
This content was last reviewed on November 20, 2006.