Lesion localization in periodic lateralized epileptiform discharges: gray or white matter.

We analyzed the results of neuroimaging studies in patients with periodic lateralized epileptiform discharges (PLEDs) or bilateral independent periodic lateralized epileptiform discharges (BIPLEDs) for localization of lesions in gray or white matter to determine if "cortical isolation" is a critical mechanism in the pathogenesis of this phenomena. We assessed 32 patients who had undergone computed tomography (CT) exclusively and 8 patients who had undergone magnetic resonance imaging (MRI) with or without CT. The superior resolution necessary for adequate lesion localization allowed use of only the MRI scans from the 8 patients. Six patients had scans with cortical and subcortical gray and white matter lesions, and 1 patient had a cortical gray matter lesion only. One patient had an indeterminate scan. No patient had white matter lesions only. Our findings in patients with PLEDs and BIPLEDs correlate with postmortem data in patients with generalized periodic EEG patterns that show consistent localization of lesions in the gray matter. These findings do not support cortical isolation as the critical or sole mechanism in PLEDs or BIPLEDs.