脑磁图和脑电图在癫痫诊治中的应用

目的:观察脑磁图、脑电图和磁共振检查在癫痫诊治中的应用,探讨脑磁图和脑电图的相关性。方法:选择38例经临床诊断的癫痫患者,已进行磁共振检查,并经脑磁图和脑电图发现异常放电。观察三种检查方法的定位符合率,比较影像检查与电生理检查的关系。结果:MEG与EEG定位完全一致的有18例(47．4％),定位基本一致(致少有1个叶定位一致)的有8例(21．1％)。EEG发现双侧放电的13例中,5例与MEG定位基本一致,而EEG单侧局灶放电的25例中,20例与MEG基本一致,EEG与MEG定位符合率在单侧局灶放电患者中高(P＜0．05)。MRI发现结构异常15例,与MEG和EEG定位均一致的有6例。结论:脑磁图和脑电图定位符合率约为68．5％。在单侧局灶放电中, MEG与EEG相结合可使致痫灶定位更加准确。     

Combined electroencephalography and magnetoencephalography of interictal spikes in benign rolandic epilepsy of childhood

ObjectiveThe neurogenesis and functional organization of the interictal spikes in benign rolandic epilepsy of childhood (BREC) still remains controversial.MethodsWe performed a combined neuroelectric and neuromagnetic study in 24 consecutive patients with BREC using a 143-channel whole-head magnetoencephalography (MEG) system simultaneously with electroencephalography (EEG) recorded from 40 closely spaced scalp-EEG electrodes. Isopotential and isofield maps were calculated over the time window from 250 ms before to 250 ms after the maximum of the negative peak of the spike. We then performed principal component analysis (PCA) and spatio-temporal dipole modeling in order to estimate the number, location and temporal activity of sources.ResultsEEG and MEG spikes were characterized by a stereotypical appearance both within and across patients showing a stable dipolar field distribution over the entire time window. The spikes were generated by a single tangential dipolar source located in the precentral gyrus with the positive pole directed frontally and the negative pole directed centro-temporally.ConclusionsOne source located in the precentral gyrus can adequately explain the spike complex in BREC.SignificanceSimultaneous EEG and MEG provide comprehensive information on functional organization of spikes in BREC.     

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

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). METHODS: We simultaneously recorded scalp EEG and MEG data from 43 patients with intractable focal epilepsy. Raw EEG and MEG waveforms were reviewed independently by two experienced epileptologists, one for EEG and one for MEG, blinded to the other modality and to the clinical information. The number and localization of spikes detected by EEG and/or MEG were compared in relation to clinical diagnosis based on postoperative seizure freedom. RESULTS: Interictal spikes were captured in both EEG and MEG in 31, in MEG alone in eight, in EEG alone in one, and in neither modality in three patients. The number of detections ranged widely with no statistical difference between modalities. A median of 25.7% of total spikes was detectable by both modalities. Spike localization was similarly consistent with the epilepsy diagnosis in 85.2% (EEG) and 78.1% (MEG) of the patients. Inaccurate localization occurred only in those cases with very few spikes detected, especially when the detections were in one modality alone. CONCLUSIONS: Interictal epileptiform discharges are easily perceived in MEG. Independent spike identification in MEG can provide clinical results comparable, but not superior, to EEG. Many spikes were seen in only one modality or the other; therefore the use of both EEG and MEG may provide additional information.     

The association of epileptic focus estimated by magnetoencephalography with cognitive function in non-lesional epilepsy with continuous spikes and waves during slow wave sleep (ECSWS) children

Objective

Epilepsy with continuous spikes and waves during slow sleep (ECSWS) is associated with cognitive deficits. The underlying mechanism is thought to relate to disturbance of functions of the foci by the persistent epileptic activity. However, the relationship between epileptic foci and cognitive deficits remains largely unknown, except for in Landau–Kleffner syndrome. The aim of this study was to evaluate the relationship of epileptic foci estimated from magnetoencephalography (MEG) with cognitive functions at the period of diagnosis in non-lesional ECSWS children, excluding those with Landau–Kleffner syndrome.

Evaluation of epileptic patients by means of magnetoencephalography

Studies of the magnetoencephalogram (MEG) in epileptic patients suffering from focal epilepsies showed that activities in the MEG appear which are detectable in the scalp-recorded electroencephalogram. A novel technique was developed (Anninos et al., 1987) characterized by mapping the scalp distribution of the amplitude of the spectral components (or specific bands) of the MEG and which was termed "ISO-Spectral-Amplitude (ISO-SA) mapping." The most important findings in the 19 patients we studied from these maps were that in the frequency domain 2-7 HZ the major concentrated activity were projected on the scalp of the epileptic focus. Thus with the above noninvasive method we believe that it is possible to determine the localization of epileptiform foci via a method which will be a very useful tool for clinicians.     

Magnetoencephalographic spikes not detected by conventional electroencephalography.

OBJECTIVE: To investigate some of the reasons why magnetoencephalographic (MEG) spikes are at times not apparent in conventional electroencephalograms (EEG) when the data are co-registered, and to explore to what extent modern EEG analysis methods can improve the yield. METHODS: Seventy seconds of MEG-EEG co-registration on a 122 channel Neuromag system were studied in a 10-year-old boy with Landau-Kleffner syndrome. Twenty-six EEG channels were originally recorded with a left ear reference. The EEG data were subsequently reformatted (BESA) to a variety of montages for the 10-20 and 10-10 electrode array. A 10 s data epoch was compared in detail for concordance between MEG and EEG spikes. To detect the characteristics of hidden low voltage EEG spikes, MEG spikes were averaged and compared with the concomitant averaged EEG spike. RESULTS: While there was an abundance of EEG as well as MEG spikes on the left; definite right-sided spikes were not visible in the EEG. Right hemispheric MEG spikes were, however, plentiful with an average strength of 757 fT. When the individual MEG spikes from the right hemisphere were compared with the corresponding EEG events their amplitude ranged between 24 and 31 microV and were, therefore, indistinguishable from background activity. The majority of them became visible, however, with further sophisticated data analysis. CONCLUSIONS: When the relative merits of MEG versus EEG recordings for the detection of epileptogenic spike are investigated the 10-20 system of electrode placement and conventional methods of EEG analysis do not provide optimal data assessment. The use of the 10-10 electrode array combined with modern methods of digital data analysis can provide better concordance with MEG data.     

Ictal onset localization of epileptic seizures by magnetoencephalography

OBJECTIVES: The aim of this study was to localize the ictal onset zone of focal epileptic seizures by magnetoencephalography (MEG) and to compare the results with interictal MEG localizations, ictal and interictal electroencephalography (EEG) results and magnetic resonance imaging (MRI) in epilepsy surgery candidates. MATERIALS AND METHODS: Data of 13 patients with partial seizures during MEG recording were analysed. Measurements were performed with a Magnes II dual unit system. RESULTS: In six of 13 cases, the ictal onset zone could be localized by MEG, with all interictal MEG findings being confirmed by ictal MEG results. In four cases, the ictal MEG localization results were corresponding to the ictal EEG localization results. In two cases, EEG yielded no comparable information. CONCLUSION: Ictal onset localization is feasible with MEG. Both interical and ictal MEG contribute valuable information to the presurgical assessment of epilepsy patients.     

Inhibitory phenomena during NREM sleep related to auditory stimuli and epileptic spikes

Auditory stimuli induce facilitation of the H reflex during wakefulness (so-called audio-spinal influence). In 5 subjects we found that, during SWS, the same stimuli may provoke phasic losses of muscle tone and H reflex inhibition. Similar losses of tone and H reflex inhibition were related to epileptic spikes in 3 patients.     

Detection of changes of high-frequency activity by statistical time-frequency analysis in epileptic spikes

ObjectiveA novel type of statistical time-frequency analysis was developed to elucidate changes of high-frequency EEG activity associated with epileptic spikes.MethodsThe method uses the Gabor Transform and detects changes of power in comparison to background activity using t-statistics that are controlled by the false discovery rate (FDR) to correct type I error of multiple testing. The analysis was applied to EEGs recorded at 2000 Hz from three patients with mesial temporal lobe epilepsy.ResultsSpike-related increase of high-frequency oscillations (HFOs) was clearly shown in the FDR-controlled t-spectra: it was most dramatic in spikes recorded from the hippocampus when the hippocampus was the seizure onset zone (SOZ). Depression of fast activity was observed immediately after the spikes, especially consistently in the discharges from the hippocampal SOZ. It corresponded to the slow wave part in case of spike-and-slow-wave complexes, but it was noted even in spikes without apparent slow waves. In one patient, a gradual increase of power above 200 Hz preceded spikes.ConclusionsFDR-controlled t-spectra clearly detected the spike-related changes of HFOs that were unclear in standard power spectra.SignificanceWe developed a promising tool to study the HFOs that may be closely linked to the pathophysiology of epileptogenesis.     

Detectability of cerebellar activity with magnetoencephalography and electroencephalography

Electrophysiological signals from the cerebellum have traditionally been viewed as inaccessible to magnetoencephalography (MEG) and electroencephalography (EEG). Here, we challenge this position by investigating the ability of MEG and EEG to detect cerebellar activity using a model that employs a high‐resolution tessellation of the cerebellar cortex. The tessellation was constructed from repetitive high‐field (9.4T) structural magnetic resonance imaging (MRI) of an ex vivo human cerebellum. A boundary‐element forward model was then used to simulate the M/EEG signals resulting from neural activity in the cerebellar cortex. Despite significant signal cancelation due to the highly convoluted cerebellar cortex, we found that the cerebellar signal was on average only 30–60% weaker than the cortical signal. We also made detailed M/EEG sensitivity maps and found that MEG and EEG have highly complementary sensitivity distributions over the cerebellar cortex. Based on previous fMRI studies combined with our M/EEG sensitivity maps, we discuss experimental paradigms that are likely to offer high M/EEG sensitivity to cerebellar activity. Taken together, these results show that cerebellar activity should be clearly detectable by current M/EEG systems with an appropriate experimental setup.     

Nap polygraphic recordings after partial sleep deprivation in patients with suspected epileptic seizures.

A review of the literature shows that nap recordings make a significant contribution to epilepsy studies, providing evidence of specific EEG findings in patients suspected of having epilepsy. In addition, sleep deprivation can cause paroxysmal EEG activity and clinical seizures. We studied retrospectively 686 patients, 51.8% males and 48.2% females, who had experienced at least one episode classified from the clinical point of view as epileptic in origin. They were divided into six age groups. Patients underwent a two-hour (1 P.M.-3 P.M.) nap-video-polygraphic recording (EEG 13 channels using the standard 10-20 system, EOG, ECG, EMG and respiration), following a partial sleep deprivation (1 to 3 h) the night before. A second recording was made in 40 patients. In 35.3% of patients, a complete sleep cycle was obtained; in 64.6% sufficient light and deep NREM sleep was obtained, but not REM stage; in 9.3%, we only observed drowsiness and stage 1 of sleep, and this group was excluded from the analysis. Interictal and/or ictal epileptic discharges were observed during the first nap recording in 245 patients (40.4% of the sample). In addition, in 40 patients (11%) with normal or inconclusive first nap EEG, a second recording was able to demonstrate epileptic abnormalities in 35% of cases. Because of its good cost/benefit ratio and availability in most western laboratories, we consider the 'nap plus partial sleep deprivation' method as advantageous over other activation procedures.     

A study of the diagnostic value of waking and sleep EEGs after sleep deprivation in epileptic patients on anticonvulsive therapy

One hundred and twenty-seven waking and sleep EEGs were recorded from 102 epileptic patients on anticonvulsant therapy, after sleep deprivation. Epileptiform activity was found in 63% of the patients, or 57% of the records. Since in previously recorded waking EEGs epileptic discharges had been registered in 19%, or 17% respectively, the rate of increase was considerable. The rate of activation was 51% in patients without epileptic activity in their waking EEGS. Two-thirds of the epileptiform activity were already recorded in the waking EEGS, after sleep deprivation, One-third was recorded only during sleep. Epileptic discharges in the different sleep stages ranged from 25% (E) to 48% (C). On the other hand, approximately the same frequency was recorded in the separate sleep stages in patients whose waking EEGS after sleep deprivation showed epileptiform activity. The EEG changes were correlated with the different clinical parameters (type of seizure, frequency and duration of seizures, age at the first seizure and the time of examination, neurological findings, and personality changes).     

Human sleep spindle characteristics after sleep deprivation

OBJECTIVE: Sleep spindles (12-15 Hz oscillations) are one of the hallmarks of the electroencephalogram (EEG) during human non-rapid eye movement (non-REM) sleep. The effect of a 40 h sleep deprivation (SD) on spindle characteristics along the antero-posterior axis was investigated. METHODS: EEGs during non-REM sleep in healthy young volunteers were analyzed with a new method for instantaneous spectral analysis, based on the fast time frequency transform (FTFT), which yields high-resolution spindle parameters in the combined time and frequency domain. RESULTS: FTFT revealed that after SD, mean spindle amplitude was enhanced, while spindle density was reduced. The reduction in spindle density was most prominent in the frontal derivation (Fz), while spindle amplitude was increased in all derivations except in Fz. Mean spindle frequency and its variability within a spindle were reduced after SD. When analyzed per 0.25 Hz frequency bin, amplitude was increased in the lower spindle frequency range (12-13.75 Hz), whereas density was reduced in the high spindle frequency range (13.5-14.75 Hz). CONCLUSIONS: The observed reduction in spindle density after SD confirms the inverse homeostatic relationship between sleep spindles and slow waves whereas the increase in spindle amplitude and the reduction in intra-spindle frequency variability support the hypothesis of a higher level of synchronization in thalamocortical cells when homeostatic sleep pressure is enhanced.     

The value of partial sleep deprivation as a routine measure in pediatric electroencephalography

For more than 50 years it has been known that in patients with epilepsy, sleep markedly increases the diagnostic yield of the electroencephalogram (EEG). Sleep deprivation could have an additional activating role. Many laboratories do not use these methods routinely but reserve them for a second EEG if equivocal or negative findings are present in the initial EEG. We studied a regime of routine partial sleep deprivation without the use of hypnotic agents in 396 children younger than age 17 years who were referred for EEG with a diagnosis of epilepsy or suspected epilepsy. Sleep was achieved for the EEG in 77% (96% in the 1 month to 2 year age group, 78% in the 2 to 8 year age group, and in 64% of those more than 8 years old). In a comparison group of 72 children who had not been sleep-deprived, sleep was achieved in 44% (69% of those less than 2 years old, 27% of those between 2 and 8 years of age, and 33% of those older than 8 years). The differences were highly significant. The regime was well tolerated. Routine partial sleep deprivation is a practical and effective method of obtaining sleep and thus maximizing the information obtained from a single EEG.     

Mapping the signal-to-noise-ratios of cortical sources in magnetoencephalography and electroencephalography

Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal-to-noise-ratios (SNRs) of cortical sources in MEG and EEG. Data from four subjects were used to simulate focal and extended sources located on the cortical surface reconstructed from high-resolution magnetic resonance images. The SNR maps for MEG and EEG were found to be complementary. The SNR of deep sources was larger in EEG than in MEG, whereas the opposite was typically the case for superficial sources. Overall, the SNR maps were more uniform for EEG than for MEG. When using a noise model based on uniformly distributed random sources on the cortex, the SNR in MEG was found to be underestimated, compared with the maps obtained with noise estimated from actual recorded MEG and EEG data. With extended sources, the total area of cortex in which the SNR was higher in EEG than in MEG was larger than with focal sources. Clinically, SNR maps in a patient explained differential sensitivity of MEG and EEG in detecting epileptic activity. Our results emphasize the benefits of recording MEG and EEG simultaneously.     

The epileptic syndromes with continuous spikes and waves during slow sleep: definition and management guidelines

The authors propose to define the epileptic syndromes with continuous spikes and waves during slow sleep (CSWS) as a cognitive or behavioral impairment acquired during childhood, associated with a strong activation of the interictal epileptiform discharges during NREM sleep--whatever focal or generalized--and not related to another factor than the presence of CSWS. The type of syndrome will be defined according to the neurological and neuropsychological deficit. These syndromes have to be classified among the localization-related epileptic syndromes. Some cases are idiopathic and others are symptomatic. Guidelines for work-up and treatment are proposed.