Interictal and Ictal EEG Patterns

Abstract

EEG is a very useful tool for detecting epileptiform abnormalities, cerebral disturbances, and clinical/subclinical seizures. Spikes and sharp waves are epileptiform discharges, standing out from the background and frequently associated with after coming slow waves. They have the same clinical significance but are different in duration. Spikes have duration of <70 msec and sharp waves between 70 and 200 msec. Epileptiform discharges can be focal or generalized. The type and frequency of discharges may help diagnose specific epileptic syndrome. For example generalized 3 Hz spike and waves are seen in absence epilepsy and 4–5 Hz atypical spike and waves/polyspikes are seen in juvenile myoclonic epilepsy. A seizure is defined as sustained repetitive epileptiform activity, or rhythmic theta and delta activity evolving in time and space. This chapter describes the most important ictal and interictal EEG patterns.