Ictal EEG Patterns Research Articles

Localization of Temporal Lobe Foci by Ictal EEG Patterns

Identifying patients whose complex partial seizures originate in temporal neocortex rather than in hippocampus is important because such patients have less favorable outcomes with standard anteromesial temporal resections. We reviewed scalp-recorded ictal EEGs of 93 epilepsy surgery candidates who either underwent intracranial EEG monitoring (n = 58) or who were referred directly for temporal lobectomy (n = 35). We definded seven patterns of early seizure discharges, grouped patients according to their seizure pattern, and correlated these with the site of seizure onset determined by intracranial EEG. Categorization by seizure pattern was also compared with brain magnetic resonance imaging (MRI) findings intracarotid amobarbital (Wada) testing. An initial, regular 5- to 9- Hz inferotemporal rhythm (type 1A) was most specific for hippocampal-onset seizures. Less commonly, a similar vertex/parasagittal positive rhythm (type 1B) or a combination of types 1B and 1A rhythms (type 1C) was recorded. Seizures originating in temporal neocortex were most often associated with irregular, polymorphic, 2- to 5-Hz lateralized activity (type 2A). This pattern was commonly followed by a type 1A theta rhythm (type 2B) or was preceded by repetitive, sometimes periodic, sharp waves (type 2C). Seizures without a clear lateralized EEG discharge (type 3) were most commonly of temporal neocortical origin. These associations between type of seizure pattern and probable site of cerebral origin were statistically significant. MRI and Wada testing did not have as much specificity as ictal patterns in differentiating among seizure origins. We conclude that the initial pattern of ictal discharge on scalp EEG can assist in distinguishing seizures of temporal neocortical onset from those of hippocampal onset. This information can be used to identify patients for invasive monitoring.

Preoperative EEG correlates of seizure outcome from epilepsy surgery in children

To identify criteria for selecting pediatric candidates for cortical resection, we compared preoperative standard EEGs, extracranial or intracranial (subdural strip or grid) electrode EEG-video monitoring and imaging studies, and surgical pathology findings with long-term (mean = 6.1 years) seizure outcome. Of 47 children, 83% were either seizure-free or substantially improved. Children with a predominant single interictal focus in standard EEGs over time or with seizures that were mostly well localized (even with equal numbers of bilaterally independent spikes) during monitoring had significantly better outcomes than those who had mostly diffuse or bilaterally independent interictal and ictal discharges. Factors not associated with poor outcomes were some seizures unaccompanied by ictal EEG patterns, spikes in postresection electrocorticograms, extratemporal resection, younger age at surgery, and older age of seizure onset. Significantly more patients with than without tumors were seizure-free. Significantly more preteenagers than teenagers had poorly localized interictal and ictal discharges.

The correlation of interictal spikes and ictal EEG patterns with postsurgical outcomes in temporal lobe epilepsy patients

The correlation of interictal spikes and ictal EEG patterns with postsurgical outcomes in temporal lobe epilepsy patients

So-called “Petit Mal Status”: Epileptic syndrome or seizure type?

In 1945, Lennox was the first to describe the epileptic states mainly expressed by various degrees of consciousness disturbance, which have their onset in children who present epileptic absences correlated with ictal EEG patterns of spike-wave complex discharges at about 3 Hz. As the clinical picture seemed to be similar to an uninterrupted series of absences, this led to the definition "Petit Mal Status" (PMS). Many authors have subsequently reported that PMS can occur in epileptic subjects who have never presented absences (and even in subjects without a previous history of epilepsy) and that the related EEG pictures were characterised by paroxysmal generalized activity of various morphology, but hardly ever consisted of the continuous rhythmic spike-wave or polyspike-wave complexes at 3 Hz found in petit mal absences. Finally, in reporting the onset and recurrence of this condition typically in adults and the elderly, some authors have proposed the existence of a particular form of PMS (dependent on different types of pathologic factors and characterising a specific syndrome of this age) that is different from that of the "real PMS" typical of childhood and related to petit mal absences. This paper describes fifteen patients in whom the onset of the condition occurred at different ages, and who seem to exemplify the various possible clinical expressions of PMS, with the aim of making a contribution towards the better nosographic definition of this epileptic condition. On the basis of our study, we sustain that the so-called PMS is a seizure type of Idiopathic Generalized Epilepsy which may appear at nearly all ages, and may occur in isolation or in association with other epileptic manifestations, but cannot itself be considered as characterising one or more age-dependent syndromes.

Unethical research relating to Helicobacter pylori?

<h3>Abstract</h3> Spike and wave discharges (SWDs) of absence epilepsy are considered as pathologic alterations of sleep spindles; however, their network-level relationship has never been convincingly revealed. In order to observe the development and generalization of the thalamocortical SWDs and the concomitant alterations of sleep related oscillations, we performed local field potential and single unit recordings in rats for 3 months during their maturation. We found that while SWDs and spindles look similar in young, they become different with maturation and shift to appear in different brain states. Thus, despite being generated by the same network, they are likely two distinct manifestations of the thalamocortical activity. We show that while spindles are already mainly global oscillations, SWDs appear mainly only focally in young. They become capable to generalize later with maturation, when the out-of-focus brain regions develop a decreased inhibitory/excitatory balance. These results suggest that a hyperexcitable focus is not sufficient alone to drive generalized absence seizures. Importantly, we also found the gradual age dependent disappearance of sleep spindles coinciding with the simultaneous gradual emergence of spike-and-waves, which both could be reversed by the proper dosing of ethosuximide. Based on these observations we conclude that the absence seizure development might be a multi-step process, which might involve the functional impairment of cortical interneurons and network-level changes that negatively affect sleep quality. <b>Significance statement</b> Absence seizure development parallels with the deterioration of slow wave sleep, which might be reversible with ethosuximide in a narrow therapeutic range, but not with early electrical seizure abruption. Thus, by proper dosing, spindles can be pharmaceutically recovered while epileptic activity is suppressed and absence related sleep and learning disturbances may be counterbalanced. We further found that despite the characteristic high voltage rhythmic global ictal EEG patterns the absence seizures are not accompanied with widespread phase-locking of neuronal activities.

Effect of anterior callosotomy on bilaterally synchronous spike and wave and other EEG discharges.

We analyzed pre- and postoperative interictal and ictal EEG patterns in relation to seizure outcome in 29 patients with intractable epilepsy who had undergone anterior callosotomy. Twenty-two patients had generalized bilaterally synchronous sharp or spike and slow wave discharges (GSW) and 7 did not: Postoperatively, patients with preoperative GSW showed disruption of synchrony, increased amplitude asymmetry, and a decreased amount of GSW. No significant decrease was noted in the amount of total epileptic discharge after operation. There was a significant relation between seizure outcome and decrease in amount of GSW. The degree of disruption of synchrony, total amount of epileptic discharge, and pre- and postoperative EEG patterns were not good indicators of seizure outcome. Postoperative changes in lateralization of epileptic foci consisted either of increased lateralization, less lateralization but increased independent discharges in the previously nonpredominant hemisphere, or appearance of some lateralization. There appears to be a spectrum of GSW: Both secondary bilateral synchrony and secondarily generalized corticoreticular epileptic discharges are distributed along this spectrum.

Use of Scalp-Sphenoidal EEG for Seizure Localization in Temporal Lobe Epilepsy

We determined the accuracy and sensitivity of scalp-sphenoidal EEG for seizure focus localization in 50 patients who became seizure-free or had rare seizures following temporal lobectomy. EEG localization was based on concordant interpretations of scalp-sphenoidal ictal EEG by three independent interpreters. All patients became seizure-free or had rare seizures following temporal lobectomy. Localization from EEG disagreed with the side of surgery in only 1 (2%) of 50 patients. We identified 3 distinct patient groups with a low, moderate, and high likelihood of having a focal ictal EEG pattern during a seizure. These groups comprised 31% (low likelihood), 44% (moderate likelihood), and 25% (high likelihood) of patients. A model based on these results suggests that with multiple ictal EEG recordings, accurate localization from scalp-sphenoidal EEG is possible in approximately up to 65-70% of patients with temporal lobe epilepsy.

Seizure characteristics in chromosome 20 benign familial neonatal convulsions

We studied a kindred of 69 affected individuals with the autosomal dominant epileptic syndrome of benign familial neonatal convulsions, linked to chromosome 20. Forty-two percent had their seizure onset on day 3, while remission took place in 68% during the first 6 weeks. Seizures were brief and the phenotype was of a mixed seizure type, starting with tonic posture, ocular symptoms, apnea, and other autonomic features. The seizure often progressed to clonic movements and motor automatisms. The postictal state was brief, and interictally the neonates looked well. The ictal EEG pattern with generalized suppression of amplitude on onset may be relatively unique. Neurocognitive outcome was usually normal, but the risk for subsequent epilepsy was 16%. Most of the later epilepsy was generalized tonic or tonic-clonic, and some seizures were provoked, raising the possibility of an unusual form of reflex epilepsy.

Ictal clinical electroencephalographic findings of spasms in West syndrome.

The electroencephalographic/video recordings of 955 spasms in children with cryptogenic and symptomatic West syndrome (WS) were reviewed to define the relation between a clinical manifestation of a spasm and its EEG pattern, and to examine whether these features reflect the etiology and prognosis of WS. The review confirmed the spasm to be a distinct type of seizure, with a unique clinical and EEG pattern unlike that of all other recognized seizures. Symmetric spasms were present in cryptogenic and symptomatic patients. In contrast, asymmetric spasms, or focal signs recognizable during a spasm, strongly indicated the existence of a cerebral lesion. In both etiological groups, the characteristic ictal EEG pattern of the spasms consisted of a positive-vertex slow wave. The other two patterns apparently correlated to a spasm, were fast activity, here called spindle-like, and decremental activity. The fast activity corresponded to a clinical stare, and the decremental activity, when present, represented a postictal event. Although it was independent from the etiology of the spasms, persisting hypsarrhythmia during a cluster of spasms appeared to be an EEG pattern that correlated with a favorable outcome.

Scalp-recorded ictal patterns in focal epilepsy.

Scalp-recorded focal EEG seizure patterns are usually expressed as rhythmic metamorphic evolving patterns (with or without epileptiform morphology) that progress through two or more ictal phases into a postictal change. Such patterns are almost invariably seen in temporal complex partial seizures but less often detected in frontal complex partial seizures and least of all in simple partial seizures. The failure of scalp recordings to detect activity from a focal seizure can usually be explained by the seizure's distant location, limited extent, or disadvantageous orientation with respect to scalp electrodes. The elimination of these disadvantages with properly implanted electrodes explains why these recordings are able to detect seizure discharges missed by scalp electrodes. Although the lateralization of a scalp-recorded seizure can be misleading, it usually accurately identifies the focus when it remains well-lateralized throughout its various ictal phases and into the postictal state.

Non-convulsive status epilepticus in the adult mentally retarded: Classification and role of benzodiazepines

Non-convulsive status epilepticus (NCS) is rarely encountered and may appear with a psychiatric mask. As clouding of consciousness is the major ictal manifestation, the condition may easily be overlooked in the mentally retarded. We have studied 11 mentally retarded patients with NCS. Since NCS with a focal onset may have a generalized ictal EEG pattern, a classification of NCS solely based on the seizure classification may be misleading. In some patients, it is impossible, both clinically and on the basis of EEG recordings, to distinguish between continuous complex partial seizures and atypical absences. We therefore propose a revised classification of NCS based on the ictal EEG pattern and the epilepsy syndrome diagnosis (I) NCS in generalized epilepsy syndromes, (II) NCS in localization-related epilepsy, (a) with localized EEG features, (b) with generalized EEG features, and (c) with transitional EEG features, and (III) undetermined NCS. Four of our patients were classified as Group I, two as Group IIa, one as Group IIb, one as Group IIc, and three as Group III. Benzodiazepines at small or standard doses may be ineffective in terminating NCS, particularly in the Lennox-Gastaut Syndrome. The identification of trigger factors is essential. Drugs seemed to be the most important precipitants in our patients; in three, NCS was induced by recurrent rectal diazepam over-administration. This complication of rectal diazepam treatment in epilepsy has not been addressed previously.

Ictal EEG changes with corpus callosum section.

Corpus callosum section diminishes but does not completely abolish secondary bilaterally synchronous interictal EEG discharges, yet often causes cessation of generalized seizures. The effects of corpus callosum section on ictal EEG patterns have not been described. We contrasted ictal EEG patterns before and after anterior callosotomy in 18 patients and before and after total callosotomy in 10 patients. Bilaterally synchronous seizure onset was disrupted in 5 of 11 anterior section patients and 5 of 5 total section patients. Seven of 18 anterior section patients and 5 of 10 total section patients had more localized seizure onset after the procedure; localization to the frontal lobe was observed after anterior or total section, but only total section patients had newly demonstrated posterior locations of seizure onset. These data suggest that the mechanisms by which bilaterally synchronous interictal and ictal discharges are generated differ. Although brainstem or diencephalic structures may contribute to formation of interictal bilateral synchrony, the corpus callosum may be the only pathway used in producing apparent bilateral synchronous seizure onset in patients with secondarily generalized seizures.

Anterior, total, and two-stage corpus callosum section: differential and incremental seizure responses.

Published reports suggest that control of generalized seizures is improved by callosotomy but do not necessarily indicate that completion of failed anterior callosotomy is beneficial. We studied 42 patients after anterior callosotomy and 22 after total callosotomy, of whom 14 underwent a two-stage procedure. Cure or marked diminution of seizures was most dramatic for atonic and tonic-clonic seizures after anterior callosotomy (100 and 83%), and for tonic-clonic and tonic seizures after total callosotomy (68 and 57%). For the 14 patients who failed to improve after anterior section and then underwent total section, incremental responses were noted for all seizure types, with cure or marked diminution of partial seizures in 2 of 14 patients, of tonic-clonic seizures in 6 of 10, of tonic seizures in 2 of 4, of atonic seizures in 2 of 5, and of myoclonic seizures in 1 of 1. More than two seizure types, verbal IQ < 80, and diffuse ictal EEG patterns were significantly more common in the anterior callosotomy failures. Total callosotomy can be of benefit when anterior callosotomy fails, especially for persistent tonic-clonic and tonic seizures, and will most often be necessary in patients with diffuse cerebral abnormalities.

Single photon emission computed tomography study of subclinical rhythmic electrographic discharge in adults

Subclinical rhythmic electrographic discharge in adults (SREDA) is considered a benign EEG pattern of uncertain significance, although it may closely resemble an EEG seizure pattern. We investigated a 57-year-old man with a very lateralized epileptiform activity localized to the occipito-temporal areas of the right hemisphere. Neuropsychological tests, clonazepam injection and 99m Tc-HMPAO-SPECT were performed during the SREDA and compared to the interparoxysmal data, providing further evidence that SREDA cannot be considered as an epileptic pattern and that, in some instances, it may be related to chronic hypoxic/ischemic mechanisms.

Long-term EEG-video-audio monitoring: computer detection of focal EEG seizure patterns

Twelve individuals with medically refractory partial seizures had undergone EEG-video-audio (EVA) monitoring over 1–15 (mean 10.5) days. We selectively reexamined available 15-channel EEGs (video-cassettes) totaling 461 h and containing 253 EEG focal seizures. Computer analysis (CA) of these bipolar records was performed using a mimetic method of seizure detection at 6 successive computer settings. We determined the computer parameters at which this method correctly detected a reasonably large percentage of seizures (81.42%) while generating an acceptable rate of false positive results (5.38/h). These parameters were adopted as the default setting for identifying focal EEG seizure patterns in all subsequent long-term bipolar scalp and sphenoidal recordings. Factors hindering or facilitating automatic seizure identification are discussed. It is concluded that on-line computer detection of focal EEG seizure patterns by this method offers a satisfactory alternative to and represents a distinct improvement over the extremely time consuming and fatiguing off-line fast visual review (FVR). Combining CA with seizure signaling (SS) by the patients and other observers increased the correct detections to 85.38%. CA is best used in conjuncton with SS.

Secondary bilateral synchrony associated to a parasagittal tumor case report

A 32 years old woman who had postural limbic and primarily generalized tonic-clonic seizures since the age of 11 presented to us with a CT image strongly suggestive of a mesial meningioma near the right cingulum. Her ictal EEG pattern was characterized by regular 1.5-2.0 Hz sharp and slow wave complexes. A right craniotomy was performed under general anesthesia and intraoperative electroencephalographic and electrocorticographic recordings were obtained by means of scalp steel electrodes and modified cerebellar stimulation electrodes, respectively. These recordings demonstrated that surface spikes were often independent from the electrocorticographically recorded ones. Before tumor excision, electrical stimulation of the peritumoral mesial cortex resulted in an increase in the epileptic activity. The stimulation of the cavity left after tumor excision led to a prolonged electrographic seizure and neurophysiological procedures were stopped. Post-operatively, the patient has remained seizure free for 6 months and her EEG was normal. The pre-, intra- and postoperative findings in this case suggest that the gliotic peritumoral mesial cortex was at least involved in the epileptogenic process.

Unilateral Photoconvulsive Response in Agenesis of the Corpus Callosum

An 11-year-old female presented with the unusual coexistence of self-induced photogenic epilepsy and an atypical epileptiform ictal EEG pattern evoked by intermittent photic stimulation. The EEG showed irregular 2.5-4 Hz spike-wave and polyspike-wave complexes, strictly localized on the left hemisphere, and associated with impairment of consciousness and myoclonic jerking of the contralateral side of the body. A computer tomographic scan showed agenesis of the corpus callosum. According to the literature on corpus callosum section in uncontrolled epilepsies, we hypothesize that in our patient the agenesis of the corpus callosum probably prevented the generalization of the ictal EEG pattern evoked by intermittent photic stimulation.

Analysis of the Multi-Channel Epileptiform EEG Using the Markov Chains Formalism

A multi-level scheme of syntactic reduction of the epileptiform EEG data is briefly discussed and the possibilities it opens up in describing the dynamic behaviour of a multi-channel system are indicated. A new algorithm for the inference of a Markov network from finite sets of sample symbol strings is introduced. Formulae for the time-dependent state occupation probabilities, as well as joint probability functions for pairs of channels, are given. An exemplary case of analysis in these terms, taken from an investigation of anticonvulsant drug effects on EEG seizure patterns, is presented.

Prognostic significance of independent auras in temporal lobe seizures.

We performed a retrospective study of auras that occurred independently of complex partial seizures in patients undergoing continuous EEG monitoring with stereotactically implanted depth electrodes placed in mesiotemporal structures. Forty of 54 patients had a history of independent auras, and 32 of these individuals had independent auras while being monitored. Two hundred ninety-two independent auras were recorded, and EEG characteristics and subjective symptoms were analyzed with regard to surgical outcome. Most patients had ictal EEG changes with all or some of their auras. Four patients had nonlocalized or multifocal complex partial seizures despite the presence of well-localized auras, indicating that if intracranial ictal recording is used as a gold standard for localization, complex partial seizures must be recorded. Presence or absence of EEG change with auras did not affect prognosis nor did variability of ictal EEG pattern, spatial extent of initial field potential, aura duration, or character of symptoms correlate with prognosis or postoperative persistence of auras.

Apport de la stereo-EEG dans la definition du foyer epileptogene

For epilepsy, surgical success rates rely on the validity of the spatial definition of the epileptogenic focus. Clinical seizure characteristics and interictal and ictal EEG patterns have been the traditional means of localization. Electrocorticography and stereo-electroencephalography are sometimes used. With stereo-EEG, the topographic determination of an epileptogenic zone depends above all on the study of the anatomo-electro-clinical correlations evidenced during the seizures themselves. Interictal abnormalities, infra-clinical discharges, stimulations also help to evaluate the topography of the focus. Because surgical success is increased neither with stereo-EEG nor with EEG, the procedure remains controversial. But stereo-EEG allows the selection of 36% more patients for surgery by defining otherwise unidentifiable single epileptogenic foci (Spencer). Furthermore, the use of stereo-EEG in seizure disorders of extra-temporal origin is a real diagnostic benefit.