Focal versus Generalized Epilepsy—An Enigma

Abstract

The diagnosis of focal versus generalized epilepsy can be precise in classic cases, and in other instances, we see many variabilities with overlapping features or atypical features in these epilepsies. This imperfect distinction between generalized and focal epilepsiesmakes it challenging in our clinical practice. The clinical information obtained through semiology, electroencephalography, and neuroimaging is essential for diagnostic and therapeutic purposes. There are different scenarios and practical challenges we face in evaluating distinctly diverse focal versus generalized epilepsy. The presence of various overlapping features of focal andgeneralizedepilepsies, differentmanifestationsofepilepsy syndrome, and other epileptiform discharges’ characteristics may represent a continuum between focal and generalized epilepsies. There is a spectrum with generalized appearing epileptiform discharges emanating from focal epileptic activity concordant with magnetic resonance imaging (MRI) lesion for consideration of epilepsy surgery on one side and the awareness of focal clinical and electroencephalographic (EEG) features in generalized epilepsy to help select appropriate antiepileptic drugs (AEDs) and avoid inappropriate consideration for epilepsy surgery on the other side. There are other challenging scenarios where imaging modalities such as magnetoencephalography may be useful in differentiating secondarygeneralizedepileptiformdischarges versusprimary generalized discharges and the use of positron emission tomography in case of nonconcordant electroclinical data or finding a focus in difficult-to-treat generalized epilepsy. This enigma of focal and generalized epilepsies is further compounded by challenging situations with unclear semiological features, nonlocalizing or inconclusive EEG and negative MRI. The challenge of choosing appropriate antiseizure medications and finding a good epilepsy surgery candidate may help decide the prognosis. Knowing these variabilities will not only prepare us for the challenge but also highlights the importance of analyzing the electroclinical-imaging data in depth to be in concordance. This special issue of the Journal of Pediatric Epilepsy covers this enigma of focal versus generalized epilepsy. We bring together an expert panel of basic science neuroscientists, epileptologists, neuroradiologists, andneurosurgeonsto review and discuss some carefully selected topics. In this special edition, Onat and Eskazan tested the hypothesis whether the mechanisms underlying focal limbic epilepsy are distinctively diverse than those responsible for genetic generalized epilepsies (previously known as idiopathic generalized) by using a combination of electrophysiological, genetic, and pharmacological models in rats. Ahmad Marashly provided a detailed review on the use of the semiological classification coined by Lüders et al, which allows for accurate categorization, lateralization, and localization of epilepsy based solely on the semiological features. Jayaram et al provided several examples of different situations where it is still mysterious to figure out focal-onset seizures with secondary generalization versus primary generalized epilepsy. Assadsangabi et al discussed the neuroimaging modalities used in evaluating epilepsy and characteristic imaging findings by delving into structural abnormalities responsible for focal epilepsy and those that may present with generalized seizures. Sannagowdara and Khan attempted to give a general overview of available AEDs under a broad umbrella of effectiveness against focal and generalized seizures and discussed the appropriate choice of AED and their implications such as medications to avoid and best combinations to consider. The authors ended the discussion on precision medicine, where the future lies. Finally,