Any disease that causes organic damage to the brain can cause abnormalities in the EEG. There are also some functional diseases where the EEG can be abnormal, and the common ones are as follows: 1. Epilepsy. The EEG of epilepsy will show epileptic waves, which appear as sharp waves, spikes, spikes and slow waves, etc. Epilepsy is the most common functional disease that leads to abnormal EEG. In addition, if it is symptomatic epilepsy, there will also be organic structural damage to the brain. 2. Encephalitis. Encephalitis often presents with cortical involvement and diffuse abnormal EEG changes, commonly seen in viral meningitis, viral encephalitis, prion disease, etc. 3. Migraine. Migraine patients sometimes have abnormal EEG, but migraine is also a functional disease.4. Other organic diseases, such as cerebral infarction, cerebral hemorrhage, brain tumor, EEG, may have abnormalities in different cases.