I believe that many epilepsy patients have had an EEG test, which records bioelectric changes in the brain and can accurately record the changes in the brain electricity during a seizure in epilepsy patients, and is an important basis for diagnosing and categorizing epilepsy.

In actual clinical practice, only 4/5 epilepsy patients will have abnormal EEG, while the remaining 1/5 epilepsy patients may have normal EEG during the onset of epilepsy; and there are still some people with abnormal EEG who never have any seizure symptoms. Therefore, doctors need the auxiliary test of EEG to diagnose the presence or absence of epilepsy, but they should not completely rely on the EEG test. People who do not show EEG abnormalities may also show symptoms of epilepsy, so epilepsy cannot be ruled out just because the EEG is normal. It is necessary for the doctor to make a correct judgment based on the EEG results, combined with clinical manifestations, patient history and other comprehensive factors.

Some patients who have had one EEG monitoring will refuse to have a second EEG monitoring because the results are normal and they think that there is no need to do it again. In fact, a repeat EEG is very necessary. The "abnormal waves" that epilepsy exhibits can occur both during a seizure and during a non-seizure. For patients with typical seizures, it is easy to judge by EEG, but for patients with atypical seizures, it is difficult to find the existence of "abnormal waves" in one EEG examination, which requires repeated EEG monitoring to get a positive result.

Therefore, the presence or absence of epilepsy cannot be determined solely on the basis of "normal" EEG monitoring, but requires a combination of history and clinical presentation, and sometimes multiple EEGs are needed as an adjunctive test.

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Epilepsy cannot be ruled out if the EEG is normal but seizure symptoms persist. If an EEG is done between seizures, the EEG may not capture every abnormal discharge. Not all seizures result in an abnormal EEG, depending on the size and direction of the area of the brain that is discharging, the depth of the lesion, and the timing of the test.

If the EEG is normal on the first examination, a 24-hour EEG or sleep EEG, or repeated EEGs several times, preferably as soon as possible after a short period of time after the seizure, are recommended to have a better chance of detecting abnormal discharges.