Focal abnormalities in idiopathic generalized epilepsy: A critical review of the literature

Abstract

SUMMARYConventionally, epilepsy is dichotomized into distinct "focal" and "generalized" categories. However, many studies have reported so-called focal features among patients with idiopathic generalized epilepsy (IGE) in the domains of semiology, electroencephalography, neuropsychology, neuropathology, and neuroimaging. We sought to review such features and clinical implications. A Web of Science database search was conducted to identify relevant publications. Our search yielded 145 papers describing focal features involving different domains in IGE, with 117 papers analyzed after excluding abstracts and case reports. Focal semiologic features are commonly seen in IGE. There are conflicting data from studies in the domains of electroencephalography, neuroimaging, and neuropathology. Studies on neuropsychology are suggestive of frontal lobe functional deficits in juvenile myoclonic epilepsy. Most advanced neuroimaging studies demonstrate the involvement of both the thalamus and the cortex during generalized spike-wave discharges (GSWDs). A few electroencephalographic and neuroimaging studies indicate that the cortex precedes the thalamus at the onset of GSWD. Focal features may contribute to misdiagnosis of IGE as focal epilepsy. However there are methodologic limitations in the studies that affect the results. KEY WORDS: Electroencephalographic, Epilepsy semiology, Generalized seizures, Partial seizures, Neuroimaging, Neuropsychology.Idiopathic generalized epilepsy (IGE; genetic generalized epilepsy) constitutes a rubric of several electroclinical syndromes based on specific clinical features and electroencephalography (EEG) abnormalities.1,2 The traditional approach of classifying epilepsies into "focal" and "generalized" implies there can be no "focal" features in "generalized" epilepsies. However, there has been a gradual paradigm shift in the conceptualization of seizure generation and spread based on epileptic networks. This change is reflected in a recent publication by the International League Against Epilepsy (ILAE) on revised terminology of seizures and epilepsies.2 This paper conceptualizes focal seizures as those arising from networks confined to a single cerebral hemisphere, whereas generalized seizures "originate at some point within, and rapidly engage bilaterally distributed networks" including cortical and subcortical structures, leaving open the possibility of a focal origin within the network.Amid the ongoing debate and discussion about the pathogenesis and classification of IGE, a body of literature highlighting various focal features of IGE has gradually accumulated over the years. In this paper, we review the literature on focal characteristics of IGE in the domains of semiology, EEG, neuropsychology, neuropathology, and neuroimaging.

Thalamic volume reduction in drug‐naive patients with new‐onset genetic generalized epilepsy

“…Gray matter atrophy in the putamen,3, 4 caudate,4 globus pallidus3 and hippocampus5 has been identified inconsistently across studies in patients with GGE compared to healthy controls. The thalamus has shown the most consistent differences, typically volume loss3, 4, 6, 7 in patients with GGE. Morphologic abnormalities of cortex, in particular prefrontal, precentral, and posterior cingulate, have also been reported, although inconsistently 6, 8, 9, 10, 11…”

“…The thalamus has shown the most consistent differences, typically volume loss3, 4, 6, 7 in patients with GGE. Morphologic abnormalities of cortex, in particular prefrontal, precentral, and posterior cingulate, have also been reported, although inconsistently 6, 8, 9, 10, 11…”

Generalized epilepsy: Don’t look too close

“…Several papers by Seneviratne et al have already appeared on how generalized seizures and generalized EEG findings are often confounded by focal signatures (Seneviratne et al, 2014;Seneviratne et al, 2015a,b) to which one is now added (Seneviratne et al, 2015c). Many things were already known.…”

The topographical distribution of epileptic spikes in juvenile myoclonic epilepsy with and without photosensitivity

“…Over a third of people with JME also have absence seizures. (Beghi et al, 2006) Focal abnormalities such as single spikes, spike-wave complexes and slow waves are seen in 30-45% of cases (Aliberti et al, 1994;Lancman et al, 1994;Seneviratne et al, 2014). At least thirty percent of people with JME also have a photoparoxysmal response (PPR) and myoclonic jerks or generalised tonic clonic seizures triggered by flashing lights (Appleton et al, 2000;Wolf and Goosses, 1986).…”