The Role and Controversies of Electroencephalogram in Focal versus Generalized Epilepsy

Abstract

As early in 1935, Gibbs et al described electroencephalogram (EEG) features of large slow waves seen in “petit mal” seizures and change in background rhythm to a higher frequency, greater amplitude pattern in “grand mal” seizures. Studies have shown many typical EEG features in focal onset as well as generalized epilepsies2 3. It is usually easy to delineate focal epilepsy cases when EEG onset of seizures is clear as seen in Benign focal epileptiform discharges of childhood4. However, it is not uncommon to see cases where epileptiform discharges are not very clear. For example, there can be secondary bilateral synchrony or generalized onset of epileptiform discharges in some cases of focal epilepsy5 and nongeneralized EEG features is cases of generalized epilepsy like absence seizures.6 The awareness of occurrence of focal clinical and EEG features in generalized epilepsy is particularly important to help to select appropriate AEDs and also to avoid inappropriate consideration for epilepsy surgery7. Lüders et al8 have shown that multiple factors like electroclinical seizure evolution, neuroimaging (both functional and anatomical) have to be analyzed in depth before defining an epileptic syndrome. Here, we are providing few examples of different situations where it is still mysterious to figure out focal onset seizures with secondary generalization versus primary generalized epilepsy.