Evidence that juvenile myoclonic epilepsy is a disorder of frontotemporal corticothalamic networks

The purpose of this study is to determine regions of cerebral cortex activated during the onset and propagation of dense array electroencephalographic (dEEG) epileptiform discharges in patients with juvenile myoclonic epilepsy (JME), through the use of 256 channel, dense array scalp EEG recordings. Ten patients (16-58 years old) with the clinical diagnosis of JME comprised the study group. In all cases the MRI and neurological exams were normal, while standard EEG recordings documented typical “generalized” 4-6 Hz epileptiform patterns. Outpatient dEEG recordings captured epileptiform discharges in each patient. Localization of onset and spread of discharges in relation to a standard MRI model was accomplished by applying dipole fits and a distributed linear inverse method of cortically constrained source analysis. All patients showed epileptiform discharges that localized to sources that included orbitofrontal/medial frontopolar cortex, while basal-medial temporal lobe sources were observed in 5/10 subjects. In many ways similar to discharges of typical absence, epileptiform patterns in JME are usually irregular and frequently include temporal lobe structures as the dominant contributors to the discharges. We find that epileptiform discharges in patients with JME are not “generalized” in the sense of bilaterally synchronous diffuse onset. Rather, discharges have both localized onsets and a restricted cortical network during propagation that includes regions of frontal and temporal cortex.