Richard C. Burgess

Semiological seizure classification

Summary: We propose an epileptic seizure classification based exclusively on ictal semiology. In this semiological seizure classification (SSC), seizures are classified as follows:

Complications of invasive video-EEG monitoring with subdural grid electrodes

Objective: To evaluate the risk factors, type, and frequency of complications during video-EEG monitoring with subdural grid electrodes. Methods: The authors retrospectively reviewed the records of all patients who underwent invasive monitoring with subdural grid electrodes (n = 198 monitoring sessions on 187 patients; median age: 24 years; range: 1 to 50 years) at the Cleveland Clinic Foundation from 1980 to 1997. Results: From 1980 to 1997, the complication rate decreased (p = 0.003). In the last 5 years, 19/99 patients (19%) had complications, including two patients (2%) with permanent sequelae. In the last 3 years, the complication rate was 13.5% (n = 5/37) without permanent deficits. Overall, complications occurred during 52 monitoring sessions (26.3%): infection (n = 24; 12.1%), transient neurologic deficit (n = 22; 11.1%), epidural hematoma (n = 5; 2.5%), increased intracranial pressure (n = 5; 2.5%), and infarction (n = 3; 1.5%). One patient (0.5%) died during grid insertion. Complication occurrence was associated with greater number of grids/electrodes (p = 0.021/p = 0.052; especially >60 electrodes), longer duration of monitoring (p = 0.004; especially >10 days), older age of the patient (p = 0.005), left-sided grid insertion (p = 0.01), and burr holes in addition to the craniotomy (p = 0.022). No association with complications was found for number of seizures, IQ, anticonvulsants, or grid localization. Conclusions: Invasive monitoring with grid electrodes was associated with significant complications. Most of them were transient. Increased complication rates were related to left-sided grid insertion and longer monitoring with a greater number of electrodes (especially more than 60 electrodes). Improvements in grid technology, surgical technique, and postoperative care resulted in significant reductions in the complication rate.

Video-electrographic and clinical features in patients with ictal asystole.

Objective: Ictal asystole (IA) is a rare event mostly seen in patients with temporal lobe epilepsy (TLE) and a potential contributor to sudden unexplained death in epilepsy (SUDEP). Clinical and video-electroencephalographic findings associated with IA have not been described, and may be helpful in screening for high risk patients. Methods: A database search was performed of 6,825 patients undergoing long-term video-EEG monitoring for episodes of IA. Results: IA was recorded in 0.27% of all patients with epilepsy, eight with temporal (TLE), two with extratemporal (XTLE), and none with generalized epilepsy. In 8 out of 16 recorded events, all occurring in patients with TLE, seizures were associated with a sudden atonia on average 42 seconds into the typical semiology of a complex partial seizure. The loss of tone followed after a period of asystole usually lasting longer than 8 seconds and was associated with typical EEG changes seen otherwise with cerebral hypoperfusion. Clinical predisposing factors for IA including cardiovascular risk factors or baseline ECG abnormalities were not identified. Conclusion: Ictal asystole is a rare feature of patients with focal epilepsy. Delayed loss of tone is distinctly uncommon in patients with temporal lobe seizures, but may inevitably occur in patients with ictal asystole after a critical duration of cardiac arrest and cerebral hypoperfusion. Further cardiac monitoring in patients with temporal lobe epilepsy and a history of unexpected collapse and falls late in the course of a typical seizure may be warranted and can potentially help to prevent sudden unexplained death in epilepsy.

Subthalamic nucleus deep brain stimulus evoked potentials: Physiological and therapeutic implications

The effect of subthalamic nucleus (STN) stimulation on cortical electroencephalographic activity was examined in 10 patients with Parkinsons disease and 4 patients with epilepsy. Evoked potentials were created by time‐locking electroencephalography to the onset of electrical stimulation delivered through the lead implanted in the STN of patients who had previously undergone deep brain stimulation (DBS) surgery. The effect of different patterns of stimulation on the evoked response, including single‐ and paired‐pulse as well as burst stimulation, was explored. Cortical evoked potentials to single pulses were observed with latencies as short as 1 to 2 msec after a single pulse of stimulation, with activity continuing, in some cases, for up to 400 msec. Paired‐pulse experiments revealed refractory periods on the order of 0.5 msec, suggesting that stimulation of axons contributed to the generation of at least some portion of the evoked potential waveform. Evoked potentials were also present in response to 100‐msec bursts of stimulation, with some evidence that the potential was initiated within the burst artifact. The potential implications of the types of responses observed as well as potential applications are discussed.

Detection of epileptiform activity by human interpreters: blinded comparison between electroencephalography and magnetoencephalography.

Summary:  Purpose: Objectively to evaluate whether independent spike detection by human interpreters is clinically valid in magnetoencephalography (MEG) and to characterize detection differences between MEG and scalp electroencephalography (EEG).

Subdural potentials at orbitofrontal and mesial prefrontal areas accompanying anticipation and decision making in humans: a comparison with Bereitschaftspotential ☆

Field potentials associated with the execution of a warned choice Go/No-Go reaction task were recorded from prefrontal supplementary (SMA) and primary motor cortex (MI) by using subdural electrodes in 5 epileptic patients during presurgical evaluation. The choice was between a Go and a No-Go imperative stimulus (S2) in the S1-S2 paradigm. Orbitofrontal and mesial prefrontal areas generated a slow preceding potential before S2 (most likely late CNV), and bilateral mesial prefrontal areas generated a transient potential, most likely related to decision making, upon S2 in both Go and No-Go conditions. In self-paced, repetitive movement, the Bereitschaftspotential was seen only at SMA and MI, but not in the prefrontal area. The present result, therefore, suggests that in humans orbitofrontal and mesial frontal areas play an important role in preparation for cognition and in decision making, whereas SMA and MI do so in motor preparation.

Expanding the international classification of seizures to provide localization information.

In 1981, the International League Against Epilepsy took a bold step by introducing a greatly simplified seizure classification, which subsequently became the universally accepted International Classification of Epileptic Seizures (ICES). This classification employs a double dichotomy that divides the seizures into generalized and partial seizures on one side, and fur ther subdivides the par t ia l seizures into “complex” and “simple” par t ia l seizures depending on whether consciousness is lost (or altered) or preserved during the ictal event. For practical reasons, patients who were amnestic for the events occurring during the seizure are also considered to have suffered an ictal loss (or at least a significant alteration) of consciousness, and are therefore classified as having had a “complex” partial seizure.’ Compared with the older classification, which focused on the highly variable seizure symptomatology, the ICES represented a major simplification that permitted correct classification of seizures even by nonexperts. For pharmacologic treatment decisions, the dichotomies “generalized-versus-partial” and “simple-versus-complex” actually provide the most essential information regarding the drugs to select. Since partial seizures tend to respond more or less equally well to the same group of anticonvulsants independent of the site of origin of the seizure,2 no detailed subdivision of partial seizures is necessary. On the other hand, generalized seizures tend to require different pharmacologic treatments depending on the type of generalized seizure.2 Note that the ICES clearly differentiates between different types of generalized seizures that respond preferentially to one or another type of treatment2 (for example, generalized tonic-clonic seizures versus absence seizures), but does not distinguish complex partial seizures arising from different locations (for example, psychomotor seizures arising from the temporal lobe and tonic seizures with loss of consciousness arising from the supplementary motor area). The subdivision of partial seizures into “simple” and “complex” additionally emphasizes an essential characteristic that in many cases has significant repercussions on the quality of life of the epileptic patient. Specifically, most partial seizures without loss of consciousness have only a minor impact on the patient’s quali ty of life, whereas par t ia l seizures with loss of consciousness markedly disturb the patient’s life. Therefore, when evaluating the success of a treatment, it is extremely importan t to carefully analyze the impact from the standpoint of seizure type-ie, a decrease of complex partial seizures (whose abundance tends to directly affect the quality of life) is far more meaningful than a change in the frequency of simple partial seizures (which will have little effect on the quality of life). These considerations explain why the ICES has been almost universally accepted by epileptologists around the world: (1) simplicity irrespective of exact symptomatology, (2) correlation to optimal drug therapy, and (3) relationship to quality of life. However, the ICES has been less popular with neurologists evaluating epileptic patients for surgery. For characterizing focal seizures, many actually continue using one of the classic seizure classification systems, which stress seizure symptomatology as opposed to focusing on preservation or alteration of consciousness. Seizure symptomatology gives us important clues to the localization of the ictal onset zone and indirectly to the epileptogenic zone.3 Important information that can be used to localize the seizure onset zone is neglected by classifying partial seizures into merely simple and complex. Because of these shortcomings, it is logical to propose a special seizure classification for those interested in using seizure symptomatology as an important index of localization of the epileptogenic zone. Such a classification would differ fundamentally from the current ICES. In the following paragraphs, we will outline the limitations of the cur-

Subdural Recording of Ictal DC Shifts in Neocortical Seizures in Humans

Summary: Purpose: Invasive ictal EEG recording is often necessary to delineate epileptogenic areas in patients with intractable partial epilepsy, but even intracranial ictal recordings often reveal ill‐defined onset zones in neocortical epilepsy. We studied the physiologic significance of ictal direct current (DC) potentials recorded intracranially in human epilepsy.

Propagation of interictal epileptic activity in temporal lobe epilepsy

Article abstract-We recorded interictal spikes with closely spaced scalp electrodes and sphenoidal electrodes in four patients with temporal lobe epilepsy. We used multiple dipole modeling to study the number, three-dimensional intracerebral location, time activity, and functional relationship of the neuronal sources underlying the epileptic spike complexes. In all patients, we found two significant sources generating the interictal spikes which showed considerable overlap in both space and time. Source 1 was located in the mesiobasal temporal lobe and generated a restricted negativity at the ipsilateral sphenoidal electrode and a widespread positivity over the vertex. Source 2 could be attributed to the lateral temporal neocortex and was associated with a relatively restricted negativity at the ipsilateral temporal electrodes and a more widespread positivity over the contralateral hemisphere. The sources were well separated in space, with an average distance of 45 mm between them. The time activities of both sources showed similar biphasic patterns, with the mesial source leading the lateral source by approximately 40 msec, suggesting propagation of interictal epileptic activity from the mesiobasal to the lateral temporal lobe. NEUROLOGY 1995;45: 118-122

Movement-related potentials associated with single and repetitive movements recorded from human supplementary motor area.

To clarify the differences of movement-related potentials (MRPs) between single and repetitive movements, MRPs with finger movements were recorded from subdural electrodes chronically implanted on the supplementary motor area (SMA) in 2 patients, and MRPs with foot movements were recorded simultaneously from the SMA and the primary motor foot area in 1 patient. Repetitive movements did not elicit larger pre-movement potentials in the SMA as compared with single movements in all 3 patients. In the negative motor area, where electrical stimulation elicited inhibitory responses of voluntary movements and which is located at the rostral part of the SMA, pre-movement potentials to either single or repetitive movements were of approximately equal amplitude in 1 out of 3 patients. It is, therefore, most likely that the SMA plays an equally significant role in preparation for single and repetive voluntary movements.