Origin and Propagation of Epileptic Spasms Delineated on Electrocorticography

Abstract

Summary:Purpose: Ictal electrographic changes were analyzed on intracranial electrocorticography (ECoG) in children with medically refractory epileptic spasms to assess the dynamic changes of ictal discharges associated with spasms and their relation to interictal epileptiform activity and neuroimaging findings.Methods: We studied a consecutive series of 15 children (age 0.4 to 13 years; nine girls) with clusters of epileptic spasms recorded on prolonged intracranial subdural ECoG recordings, which were being performed for subsequent cortical resection, and in total, 62 spasms were analyzed by using quantitative methods.Results: Spasms were associated with either a "leading" spike followed by fast-wave bursts (type I: 42 events analyzed quantitatively) or fast-wave bursts without a "leading" spike (type II: 20 events analyzed quantitatively). Twenty-three of the 42 type I spasms but none of the 20 type II spasms were preceded by a focal seizure. A "leading" spike had a focal origin in all 42 type I spasms and involved the pre-or postcentral gyrus within 0.1 s in 37 of these spasms. A leading spike was associated with interictal spike activity >1/min in 40 of 42 type I spasms and originated within 2 cm from a positron emission tomography glucose hypometabolic region in all but two type I spasms. Failure to resect the cortex showing a leading spike was associated with poor surgical outcome (p = 0.01; Fisher's exact probability test). Fast-wave bursts associated with spasms involved neocortical regions extensively at least in two lobes within 1.28 s in all 62 spasms and involved the pre-or postcentral gyrus in 53 of 62 spasms.Conclusions: Epileptic spasms may be triggered by a focal neocortical impulse in a subset of patients, and a leading spike, if present, might be used as a marker of the trigger zone for epileptic spasms. Rapidly emerging widespread fast-wave bursts might explain the clinical semiology of epileptic spasms.

Young patients with focal seizures may have the primary motor area for the hand in the postcentral gyrus

“…For chronic subdural EEG recording and subsequent functional cortical mapping, platinum grid electrodes (10 mm intercontact distance, 4 mm diameter; Ad-tech, Racine, WI) were surgically implanted as previously described (Asano et al, 2005). The total number of electrode contacts in each subject ranged from 64 to 128.…”

“…All electrode plates were stitched to adjacent plates and/or the edge of dura mater, to avoid movement of subdural electrodes after placement. In addition, intraoperative pictures were taken with a digital camera before dural closure, to confirm the spatial accuracy of electrode display on three-dimensional brain surface reconstructed from MRI (Asano et al, 2005).…”

“…Chronic subdural EEG recordings were performed for 2−7 days as previously described (Asano et al, 2005). Anti-epileptic medications were discontinued or reduced during subdural EEG monitoring until a sufficient number of habitual seizures were captured.…”

Effect of sleep on interictal spikes and distribution of sleep spindles on electrocorticography in children with focal epilepsy

“…All signals were re-montaged to an average reference (Hart et al, 1998;Asano et al, 2005). In short, three distinct 10-minute ECoG segments during quiet wakefulness as well as sleep with central spindles were selected from the video-ECoG data, based on the following criteria: at least a 3-hour interval between each segment; at least 8 hours after a secondarily generalized tonic clonic seizure and at least 2 hours after other types of clinical seizures (Asano et al, 2003).…”

“…(D) The topography of central spindles was delineated on his own three-dimensional reconstructed surface MR image, using a method similar to that previously described (Asano et al, 2004b). To obtain referencefree topographic maps of spectral measures, all signals were re-montaged to an average reference (Hart et al, 1998;Asano et al, 2005). A total of 40 1.28-second epochs of interest were placed on sleep ECoG segments exactly showing central spindles, and an averaged amplitude spectral curve was created for each epoch.…”