EEG morphology of partial epileptic seizures.

We studied the EEG features of partial seizures in 66 patients. An EEG evolution (morphology and/or frequency change) characterised 79% of attacks: 92% of 48 events with clinical features, but only 44% of 18 subclinical seizures. Aside from attenuation which initiated 7 seizures (11%), 31 (47%) began with sinusoidal waves, 25 (39%) with repetitive epileptiform potentials, and 10 (15%) with both phenomena. Metamorphosis between these forms occurred in about 1/3 of seizures beginning with either form alone. A wave form change occurred in 44% of clinical attacks but only 7% of subclinical seizures. Spikes and sharp waves were the most common repetitive epileptiform potentials encountered. Repetition rate of phenomena at onset usually lay in the theta or delta range except for a few with high frequency sinusoidal waves. Further ictal EEG progression was more likely to occur if a mixed frequency change or frequency increase characterised early evolution.