Factors in the Interictal Record Predicting an Ictal Episode: A Case Study

This report deals with a patient with intractable seizures, who had 64 subdural electrodes implanted onto the left frontal and temporal cerebral cortex in anticipation of probable seizure surgery. One specific region on the left frontal lobe proved to be the focus for both the interictal spikes and also for the ictal activity. Our goal was to determine what electrical characteristics in the interictal record predicted the ictal episodes. The number of interictal spikes and also the amount of fast activity (15–128/sec) progressively increased before each of the 5 ictal episodes; an analysis showed that the number of spikes and their frequency proved the more significant variable. One other characteristic that changed before the ictal episodes was a great decrease in the interval between spikes as an example of a diminishing variability or increasing periodicity. Thus, the important factors in the interictal record that lead to an ictal event are the number of spikes, the amount of fast activity and the decreasing variability between the spikes.