Temporal lobe dysembryoplastic neuroepithelial tumour: significance of discordant interictal spikes.

PURPOSE: Dysembryoplastic neuroepithelial tumours (DNET) are an important cause of refractory partial epilepsies. They usually occur within dysplastic cortex and tend to affect the temporal lobes. The EEG of these patients is characterised by slowing and/or epileptiform abnormalities with a multifocal distribution. We studied the EEG features of epilepsy patients with a temporal lobe DNET to assess the relationship of EEG abnormalities with the localisation of the tumour and the clinical features. METHODS: We retrospectively reviewed 16 patients with unilateral, temporal lobe DNET on MRI. The EEG abnormalities were classified as concordant to the lesion when the EEG discharges were confined to the ipsilateral temporal lobe or discordant when EEG discharges were found in other areas. Clinical and epilepsy characteristics were compared between patients with concordant and discordant EEG. RESULTS: Focal EEG abnormalities were found in 81% of the patients; 6/16 patients had concordant EEG abnormalities, and 7/16 patients had discordant EEG abnormalities. Epilepsy severity prior to the operation, antecedents and post-operative outcome were not different between patients with concordant or discordant EEG abnormalities. CONCLUSION: Patients with temporal lobe DNET often show EEG discharges discordant to the tumour. However, they do not appear to predict the clinical and epilepsy characteristics of these patients.     

Temporal receptive fields, spikes, and Hebbian delay selection.

The intriguing concept of a receptive field evolving through Hebbian learning, mostly during ontogeny, has been discussed extensively in the context of the visual cortex receiving spatial input from the retina. Here, we analyze an extension of this idea to the temporal domain. In doing so, we indicate how a particular spike-based learning rule can be described by means of a mean-field learning equation and present a solution for a couple of illustrative examples. We argue that the success of the learning procedure strongly depends on an interplay of, in particular, the temporal parameters of neuron (model) and learning window, and show under what conditions the noisy synaptic dynamics can be regarded as a diffusion process.     

The prognostic value of residual spikes in the postexcision electrocorticogram after temporal lobectomy

We correlated the postresection electrocorticograms (ECoGs) of 80 patients who underwent temporal lobectomy under general anesthesia for treatment of intractable complex partial seizures with surgical results in three groups: seizure/aura free (32 patients), auras only (16 patients), and one or more postoperative seizures (32 patients) at mean follow-up times of 34, 31, and 38 months, respectively. Spontaneous "residual spikes," ie, present after all resections, were present in 47% of patients who had no postoperative seizures or auras. However, they occurred in 72% of patients with any postoperative seizures (p less than 0.05). The location (convexity, mesial, or edge of resections) or the distribution (unifocal versus multifocal) of the residual spikes was not of prognostic value. Quantitative studies in 5-minute epochs of the postexcision ECoGs did not reveal a significant difference in the morphology of the residual spikes, ie, the amplitude or firing pattern (single versus polyspike), in the three groups. The group with postoperative seizures showed a higher number of spikes per epoch (greater than or equal to 50), but it was not significant. Although the study shows that patients with residual spikes may have good prognosis, they are at significantly higher risk for postoperative seizures as compared with those without residual spikes. The possibility that intensity of firing of residual spikes may be an additional predictor of outcome warrants further study.     

Temporal and extratemporal BOLD responses to temporal lobe interictal spikes

PURPOSE: Simultaneous EEG and functional MRI (fMRI) allows measuring metabolic changes related to interictal spikes. Our objective was to investigate blood oxygenation level-dependent (BOLD) responses to temporal lobe (TL) spikes by using EEG-fMRI recording. METHODS: We studied 35 patients who had a diagnosis of temporal lobe epilepsy (TLE) and active TL spiking on routine scalp EEG recording. Two-hour sessions of continuous EEG-fMRI were recorded, and spikes were identified after offline artifact removal and used as events in the fMRI analysis. Each type of spike was analyzed separately, as one EEG-fMRI study. We determined significant (p < 0.05) positive (activation) and negative (deactivation) BOLD responses for each study. RESULTS: Twenty-seven patients had spikes during scanning (19 unilateral and eight bilateral). From a total of 35 fMRI studies, 29 (83%) showed BOLD responses: 14 had both activations and deactivations; 12, activations only; and three, deactivations only. Six (17%) showed no responses. Nineteen studies had mainly neocortical TL activation: Sixteen (84%) of 19 concordant with spikes, 12 of 16 with concomitant activation of the contralateral TL, and 16 of 19 with additional extratemporal activation; few showed exclusively mesial TL activation. Seventeen studies showed deactivation, either extratemporal plus temporal (n = 8) or exclusively extratemporal (n = 9). CONCLUSIONS: BOLD responses to TL spikes occurred in 83% of studies, predominated in the spiking temporal lobe, and manifested as activation or deactivation. Responses often involved the contralateral homologous cortex at the time of unilateral spikes and were frequently observed in extratemporal regions, suggesting that TL epileptic spikes can affect neuronal activity at a distance through synaptic connections.     

The prognostic significance of interictal epileptiform activity in postoperative EEGs of patients with mesial temporal lobe epilepsy.

It has not been established whether electroencephalography (EEG) is a contributing factor in predicting the outcome of surgery for epilepsy. We conducted a prospective study on 26 patients (M/F 14/12, age: 33 +/- 7.5 years, range 19-48) with mesial temporal lobe epilepsy (MTLE) who were followed for 2 years after surgery and who underwent routine EEG recordings 5.6 +/- 3 months (range 3-12) postoperatively. Interictal epileptiform activity (IEA) on the EEG was compared in 17 seizure-free patients to 9 patients with recurrent seizures. The two groups were similar in gender, age, febrile convulsions, trauma, family history, seizure frequency prior to surgery, epilepsy duration and number of antiepileptic drugs. Following surgery, 17 study patients (65%) became seizure free; 9 (35%) had seizure recurrence. Post-operative EEG recordings showed IEA in 8/26 study patients (31%), 3 of whom were from the seizure-free group (3/17, 18%); 5 had seizure recurrence (5/9, 56%) (p=0.078). IEAs in postoperative EEGs were less frequently demonstrated in patients who were seizure free, but the presence of postoperative IEAs does not preclude successful surgical outcome.     

Clinical staging and electroencephalographic evolution of continuous spikes and waves during sleep

Purpose: Currently, in continuous spikes and waves during sleep (CSWS) there is a lack of systematic assessments of the clinically relevant stages and the evolution of the electroencephalographic features. The aim of this study is to describe the evolution over time of clinical and electroencephalographic features in CSWS. Methods: We enrolled patients from our video‐electroencephalography (EEG) monitoring unit with CSWS and with overnight EEG studies with at least one overnight assessment per year over a minimum period of 3 years. We studied clinical presentation and electroencephalographic features. We calculated the (1) spike‐wave percentage (SWP) as the percentage of 1‐s bins containing at least one spike‐wave complex and (2) spike frequency (SF) as the number of spikes per 100 s. Key Findings: Nine children (six boys) met the inclusion criteria during a 15‐year period. Seven (78%) had an abnormal development prior to the epilepsy onset, and in two (22%) seizures were the only presenting symptom. Median age at epilepsy onset was 2 years (range 2 days to 4 years), at neuropsychological regression 5.1 years (4–7.7 years), and at seizure freedom 8.6 years (6.5–11.4 years). Median duration and range of clinically relevant stages were as follows: dormant stage (birth‐epilepsy onset median 2 years, range 2 days–4 years), prodromal stage (epilepsy onset‐neuropsychological regression 3.9 years, range 0.9–7.7 years), acute stage (neuropsychological regression‐seizure freedom 2.9 years, range 2.1–6.6 years), and residual stage (after seizure freedom). Seven patients (78%) had a structural lesion on neuroimaging. At last follow‐up (median 11.4 years, range 7.2–20.3 years), eight patients (89%) were receiving antiepileptic treatment, and all patients had residual neurocognitive deficits. During the acute stage, SWP was <85% in 13 (42%) of 31 assessments, and after seizure freedom, 3 of 5 patients (60%) had SWP >85%. Evolution of electroencephalographic patterns included increasing‐decreasing, continuously elevated, and fluctuating patterns (33.3% each). There was good correlation between SWP and SF (Spearman correlation‐coefficient = 0.942; p < 0.0001). SF, which can exceed 100%, reflected changes in electroencephalography pattern in more detail than SWP, which cannot exceed 100% and therefore has a ceiling effect. Significance: Our series systematically studied the age of occurrence of the significant clinical events. These may assist in defining clinical stages, which can provide a useful framework for future clinical trials in patients with CSWS. The severity of the epileptiform discharges on EEG did not always correlate with seizure frequency and severity; epileptiform discharges could be prominent after seizure freedom and fluctuated along the course of the disease. The values of SWP and SF correlated well, but SWP based on 1‐s bins has the potential disadvantage of a ceiling effect.     

Lateralization of interictal spikes after corpus callosotomy

Objective

Corpus callosotomy may limit secondary bilateral synchrony into the primary epileptogenic hemisphere. This study investigated whether pre-operative EEG can predict post-operative spike lateralization.

Methods

The subjects included 14 patients with medically intractable drop attacks who underwent total corpus callosotomy. Pre-operative patterns of inter-hemispheric propagation were quantified by peak-latency analysis with the template-based spike averaging technique.

Results

Postoperative lateralization of interictal spikes was observed in 5 of the 14 patients. Inter-hemispheric latency was significantly longer in these 5 patients (mean 14.0 ms, range from 0 to 78 ms, versus mean 5.2 ms, range from 0 to 29 ms, p < 0.01). The lateralization occurred in association with the presence of structural lesions (p < 0.05). The post-operative spikes were lateralized to the lesion side in 3 of 4 patients with unilateral epileptogenic lesion. Three patients presented one-way inter-hemispheric propagation pattern pre-operatively. The post-operative spikes were lateralized to the hemisphere of the leading spikes in two.

Conclusions

Interictal spikes are lateralized to the epileptogenic hemisphere in some patients after callosotomy. Lateralization can be expected in the presence of structural lesions and/or longer inter-hemispheric latency.

Significance

Analysis of pre-operative EEG spikes may predict the primary epileptogenic hemisphere before corpus callosotomy.     

The clinical significance of occipital spikes as a sole response to intermittent photic stimulation.

Forty-five patients who showed occipital spikes as a sole response to IPS have been studied over a 9 year period. Occipital spikes induced by IPS are non-specific, not constantly present and in themselves are not indicative of epilepsy. Occipital spikes alone are seen in a very small percentage of clinical photosensitive patients.     

Mild cognitive impairment in old age. Diagnostics and prognostic significance

Advances in clinical dementia research have made it possible to diagnose prodromal stages of various dementia syndromes. We present here the concept of mild cognitive impairment (MCI) as the most widely used concept for this stage of dementia processes. Necessary diagnostic procedures for MCI are presented, including clinical, neuropsychological and laboratory methods. Particularly in Alzheimer's disease it seems possible to diagnose a prodromal stage by using biomarkers and brain imaging, i.e. before the clinical dementia syndrome of the Alzheimer's type is present. When diagnosing dementia diseases in the stage of a clinical dementia syndrome, irreversible neuropathological processes are advanced. For this reason we should aim for the clinical detection of dementia disorders in the stage of mild cognitive impairment. This will lead to research on how to slow or even halt the progression of prodromal dementia.     

Automatic detection of seizures and spikes.

The recording of seizures and spikes is of primary importance in the evaluation of epileptic patients. This is not always an easy process because these events can be rare and are usually unpredictable. Since the earliest days of computer analysis of the EEG, researchers have developed methods for the automatic detection of spikes and, more recently, of seizures. The problems are complex because spikes and seizures are not clearly defined and have extremely varied morphologies. Nevertheless, it has been possible to develop automatic detection methods that can be of great assistance during long-term monitoring of epileptic patients. No method is absolutely fail-safe and all require human validation, but they save a considerable amount of time in the interpretation of long recordings. Recent developments include detection of the patterns specific to newborns, and the possibility of warning a patient or observer that a seizure is starting.     

Diagnostic and prognostic significance of electroencephalography with intravenous diazepam in epilepsy.

Thirty cases of intractable epilepsy in children were investigated to observe the correlation between the suppression of seizure discharges to intravenous diazepam and the type of seizure or effects of subsequent therapy. Suppression of seizure discharges were bilaterally poor in 75% of the cases with infantile spasms and 89% of cases with Lennox syndrome and other generalized seizures while it was unilaterally poor in 80% of the cases with focal or unilateral seizures. ACTH or steroid therapy was clinically and electroencephalographically effective in 80% of the cases with good suppression responses and in none of cases with good suppression that was resistant to the therapy. On the other hand, clinical seizures were not controlled in 73% of the cases showing poor suppression and EEG did not reveal improvement in 82% of the cases with poor suppression. EEG with intravenous diazepam is valuable for understanding the pharmacophysiological mechanism of epilepsy and it may be possible to select cases as candidates for ACTH or steroid therapy using this technique.     

Temporal lobe epilepsy: origin and significance of simple and complex auras.

The aura experience of 88 patients with temporal lobe epilepsy was recorded, classified and analysed. Despite the great richness of the 215 experiences described, correlations with left or right brain, nature of lesion, age of onset, etc. were only apparent when a classification into three aura groups was used. "Simple primitive" auras as sole auras were more likely with early onset epilepsy, in lower IQ patients, in males, from the right temporal lobe, and with mesial temporal sclerosis. Exclusively "intellectual" auras were confined to a group of high IQ males. The number of aura experiences described per person correlated with Verbal IQ for males but not females, but also varied with side, sex, and nature of lesion. The results are discussed in terms of the necessary conditions for aura and their relevance and in relationship to the results of brain stimulation studies by Penfield and others.     

Detection of epileptic spikes by magnetoencephalography and electroencephalography after sleep deprivation

IntroductionIn diagnosis of epilepsies electrophysiological findings play a key role. While spontaneous electroencephalography (EEG) and EEG with sleep deprivation (EEGsd) are widely evaluated and used, application of magnetoencephalography (MEG) in this field is primarily limited to presurgical assessment of focal epilepsies.MethodsIn this study we retrospectively compared MEG (M/EEG) and EEGsd in 63 (55) patients with focal and generalized epilepsy with regard to occurrence of epileptic spikes.ResultsMEG could record epileptic spikes in 38 patients (60%), while EEGsd recorded spikes in only 32 patients (51%). In a group of 55 patients simultaneous MEG/EEG (M/EEG) was able to record spikes in 38 patients (71%) compared to epileptic spikes in 28 patients (51%) recorded by EEGsd. In a subgroup of 17 MR-negative patients simultaneous M/EEG could record epileptic spikes in all patients, while EEGsd was successful in only 11 (64%) of them.ConclusionIn this study, MEG showed a tendency to record epileptic spikes in more patients than EEGsd. Furthermore, simultaneous M/EEG has been shown to be especially successful in detection of epileptic spikes in patients with MR-negative epilepsy. This might at least in parts be explained by neocortical predominance of MR-negative epilepsy. Thus, this study motivates prospective studies to evaluate the substitutability of EEGsd by MEG more extensively.     

Childhood absence epilepsy: evolution and prognostic factors

PURPOSE: To evaluate how diagnostic criteria influence remission rates for patients with childhood absence epilepsy (CAE) and to assess clinical and EEG parameters as predictors of outcome. METHODS: One hundred nineteen patients were diagnosed with CAE, according to International League Against Epilepsy (ILAE) classification criteria. They were subsequently evaluated according to stricter diagnostic criteria. Sixty-two subjects fulfilled these criteria as group 2; 57 did not and constituted group 1. Diagnostic parameters that prevented patients of group 1 from entering group 2, and variables such as sex, familial history of generalized epilepsy, and personal history of febrile convulsions also were tested as prognostic factors for terminal remission. RESULTS: Compared with those in group 1, patients of group 2 had significantly higher rates of seizure control (95% vs. 77%), higher rates of terminal remission (82% vs. 51%), fewer generalized tonic-clonic seizures (8% vs. 30%), and shorter mean periods of treatment (2.2 vs. 3.8 years). Significantly fewer patients were receiving polytherapy in group 2 than in group 1 (11% vs. 47%), and fewer patients had seizure relapses at antiepileptic drug discontinuation (0 vs. 22%). CONCLUSIONS: Remission rates of patients with CAE are greatly influenced by the classification criteria used for selection. Stricter diagnostic criteria allow the definition of a homogeneous group of patients with excellent prognosis. Factors predicting unfavorable prognosis were generalized tonic-clonic seizures in the active stage of absences, myoclonic jerks, eyelid myoclonia or perioral myoclonia, and EEG features atypical for CAE.     

Temporal profile of T2-weighted MRI distinguishes between pannecrosis and selective neuronal death after transient focal cerebral ischemia in the rat.

Transient middle cerebral artery occlusion (MCAO) by an intraluminal thread leads to primarily subcortical infarctions with little sensorimotor impairment in the Wistar rat strain. We investigated the course of infarct development in this lesion type for 10 weeks using magnetic resonance imaging (MRI) along with histological characterization. MCAO was induced in male Wistar rats (260 to 300 g) for 60 mins. Animals received follow-up T1- and T2-weighted MRI from day 1 until week 10. Separate groups of animals were analyzed histologically after 2, 6, and 10 weeks. Histology included immunohistochemistry for neuronal and astrocytic markers as well as hematoxylin eosin and luxol fast blue-cresyl violet staining. In contrast to lesions involving the cortex, exclusively subcortical infarctions were characterized by a complete resolution of initially increased T1 and T2 relaxation times by 10 weeks. Between 2 and 10 weeks, neuronal death and gliosis as well as a dense inflammatory infiltrate were evident in these lesions, without damage to fiber tracts or development of cystic cavities. Exclusively subcortical lesions in Wistar rats are characterized by normalization of T1 and T2 relaxation times, which might, however, not be mistaken for tissue recovery. Despite this MRI normalization, selective neuronal death and gliosis develop. Although MRI at individual time points might therefore be ambiguous, the temporal profile of relaxation time changes over the chronic time period allows discrimination of the lesion development into selective neuronal death or pannecrosis.