Ambulatory cassette EEG

The neurophysiologic evaluation of patients with possible or proven paroxysmal disorders is no longer limited to routine laboratory EEGs or intensive inpatient monitoring. Expanded temporal sampling of the EEG, which increases the probability of documenting, characterizing, and quantitating the electrographic manifestations of these illnesses, is now available on a portable, outpatient, and less cumbersome inpatient basis by means of ambulatory cassette recordings. Ambulatory EEG has evolved from clinical need and from new technology that has provided small multichannel tape recorders, miniature preamplifiers, and rapid video/audio playback units. Clinical series and controlled trials have confirmed the usefulness of cassette EEG monitoring in a wide range of neurologic disorders, particularly epilepsy. Ambulatory EEG diagnostic yields have been shown to be superior to routine laboratory studies and nearly as good as inpatient telemetry evaluations. The role of cassette recordings in clinical EEG is being redefined as new applications are established.     

Relationship between EEG and positron emission tomography abnormalities in clinical epilepsy.

Positron emission tomography (PET) is a relatively noninvasive neuroimaging method by means of which a large variety of human brain functions can be assessed. Localized neurochemical abnormalities detected by PET were found in patients with partial epilepsy and suggested the use of this modality for localizing epileptogenic regions of the brain. The clinical usefulness of PET is determined by its sensitivity and specificity for identifying epileptogenic areas as defined by ictal surface and intracranial EEG recordings. The findings obtained from comparative EEG and glucose PET data are reviewed with special emphasis on patients undergoing presurgical evaluation because of medically intractable temporal and extratemporal lobe epilepsy. The utility of glucose PET studies for identifying regions of seizure onset is presented, and the limited specificity of glucose metabolic abnormalities for the detection of various EEG patterns in clinical epilepsy is discussed. The authors review the available intracranial EEG and PET comparisons using [11C]flumazenil (FMZ) PET, a tracer for the assessment of tau-amino-butyric acid/benzodiazepine receptor function. They also summarize their experience with [11C]flumazenil PET in identifying cortical regions that show various ictal and interictal cortical EEG abnormalities in patients with extratemporal seizure origin. Finally, the authors demonstrate that further development of new PET tracers, such as alpha-[11C]methyl-L-tryptophan, is feasible and clinically useful and may increase the number of patients in whom PET studies can replace invasive EEG monitoring.     

The seizure prediction characteristic: a general framework to assess and compare seizure prediction methods

The unpredictability of seizures is a central problem for all patients suffering from uncontrolled epilepsy. Recently, numerous methods have been suggested that claim to predict from the EEG the onset of epileptic seizures. In parallel, new therapeutic devices are in development that could control upcoming seizures provided that their onset is known in advance. A reliable clinical application controlling seizures, consisting of a seizure prediction method and an intervention system, would improve patient quality of life. The question therefore arises as to whether the performance of the seizure prediction methods is already sufficient for clinical applications. The answer requires assessment criteria to judge and compare these methods, but recognized criteria still do not exist. Based on clinical, behavioral, and statistical considerations, we suggest the "seizure prediction characteristic" to evaluate seizure prediction methods. Results of this approach are exemplified by its application to the "dynamical similarity index" seizure prediction method using 582 hours of intracranial EEG data, including 88 seizures.     

Clinical neurophysiology using electroencephalography in geriatric psychiatry: neurobiologic implications and clinical utility

Electroencephalography (EEG) offers a unique contribution to the armamentarium of imaging technologies used in the evaluation of brain function. The primary clinical application of EEG is in the diagnosis of delirium, dementia, and epilepsy, which are frequently encountered in the practice of geropsychiatry. This review summarizes the principles behind generation of the EEG signal, its strengths and limitations as a technology, clinical indications for performing an EEG, the principles underlying quantitative EEG (QEEG), and how QEEG is allowing us to probe brain function and connectivity in new ways.     

An automatic procedure for the analysis of electric and magnetic mismatch negativity based on anatomical brain mapping

Data processing techniques in electroencephalography (EEG) and magnetoencephalography (MEG) need user interactions. However, particularly in clinical applications, fast and objective data processing is important. Here we present an observer-independent method for EEG and MEG analysis of mismatch negativity (MMN) that allows reliable estimation of source activity based on objective anatomical references. The procedure integrates several steps including artifact rejection, source estimation and statistical analysis. It enables the evaluation of source activity in a fully automatic and unsupervised manner. To test its feasibility we obtained EEG and MEG responses in an auditory oddball paradigm in 12 healthy volunteers. The automatized method of EEG and MEG data analysis estimated source activity. The automatically detected MMN was closely comparable with the results obtained by a user-controlled method based on the dipole fitting. The presented workflow can be performed easily, rapidly, and reliably. This development may open new fields in research and clinical applications of source-based EEG and MEG.     

A Proposed New Method for Electroencephalography Trace Recording in Children Younger Than Two Years: An Observational Study

Epilepsy is a common disorder in pediatric neurology, and electroencephalography (EEG) continues to play an important role in its diagnosis. However, the small size of a child's head and immaturity of the brain make EEG interpretation more difficult in children than in adults. This article presents a new method of EEG recording for children younger than 2 years designed to improve recording accuracy in children with small heads. This novel method of EEG recording, in which an increase in distance between recording electrodes is achieved without decreasing the number of electrodes or channels, compares with the traditional 10-20 system in terms of pathologic waves, artifacts, sleep spindles, and wave frequencies. Increased wave amplitude was noted with the new montages in 90 of 105 (85.7%) individuals. The calculation of wave frequency was easier and more reliable in the new montages in comparison with the prevailing recordings. More numerous sleep spindles were detected in 49 of 105 (47.6%) children. The number of detected pathological waves increased in 49 of 105 (47.6%) children on the new montages versus the 10-20 electrode system. The incidence of artifact waves in the traces was similar between the two methods in 94 (89.5%) patients and diminished in 11 of 105 (10.5%) patients. These preliminary studies suggest that the new recording system might be a suitable substitute for the routine 10-20 system, especially in young infants and neonates. Further evaluation and multicenter clinical trials will contribute to the reliability of this proposed method.     

Changes in QEEG prefrontal cordance as a predictor of response to antidepressants in patients with treatment resistant depressive disorder: a pilot study

INTRODUCTION: Previous studies of patients with unipolar depression have shown that early decreases of EEG cordance (a new quantitative EEG method) can predict clinical response. We examined whether early QEEG decrease represents a phenomenon associated with response to treatment with different antidepressants in patients with treatment resistant depression. METHOD: The subjects were 17 inpatients with treatment resistant depression. EEG data and response to treatment were monitored at baseline and after 1 and 4 weeks on an antidepressant treatment. QEEG cordance was computed at three frontal electrodes in theta frequency band. The prefrontal cordance combines complementary information from absolute and relative power of EEG spectra. Recent studies have shown that cordance correlates with cortical perfusion. Depressive symptoms were assessed using Montgomery-Asberg Depression Rating Scale (MADRS). RESULTS: All 17 patients completed the 4-week study. All five responders showed decreases in prefrontal cordance after the first week of treatment. Only 2 of the 12 nonresponders showed early prefrontal cordance decrease. The decrease of prefrontal QEEG cordance after week 1 in responders as well as the increase in nonresponders were both statistically significant (p-value 0.03 and 0.01, respectively) and the changes of prefrontal cordance values were different between both groups (p-value 0.001). CONCLUSION: Our results suggest that decrease in prefrontal cordance may indicate early changes of prefrontal activity in responders to antidepressants. QEEG cordance may become a useful tool in the prediction of response to antidepressants.     

Electrophysiological assessment of neuropsychiatric disorders.

In this article the clinical usefulness and limitations of the routine electroencephalogram (EEG) are discussed. Emphasis is placed on 3 specific clinical situations where EEG can be most useful: the differential diagnosis of dementia versus pseudodementia, the evaluation of episodic behavior disorders including aggressive episodes, and acute confusional states. An atypical clinical presentation is emphasized as the most important indiction for obtaining an EEG evaluation. The issue of controversial EEG waveforms is discussed in some detail. The need for well-designed, controlled studies to further examine these EEG patterns is emphasized. Finally, the limitations of the routine EEG are discussed. The article concludes with a brief mention of the future promise of other electrophysiological testing modalities such as quantified EEG, evoked potentials, and sleep studies.     

The EEG evaluation of single photon emission computed tomography abnormalities in epilepsy.

Single photon emission computed tomography (SPECT) has increasingly been used as a diagnostic procedure for localizing epileptic seizure foci and as a research tool for investigating the physiologic mechanisms underlying seizure activity. With increasing use of SPECT in localizing the seizure focus for epilepsy surgery, there arises a need to critically assess its current role in the evaluation of patients for epilepsy surgery, especially as it relates to other clinical and laboratory data used in presurgical evaluation. Ictal EEG discharge has traditionally been used as the "gold standard" against which SPECT studies are compared in assessing the latter's localizing value. However, this practice presents a major challenge because SPECT studies are often reserved for patients with nonlocalizing EEG or magnetic resonance imaging findings. Nonetheless, SPECT studies in evaluation for epilepsy surgery should always be performed with the knowledge of the patient's EEG activity preceding, during, and after the injection of the radiotracer. The advent of techniques such as subtraction SPECT with co-registration on magnetic resonance imaging (SISCOM) and computer image-guided surgery has great potential in enhancing the clinical electrophysiologic evaluation of SPECT-detected abnormalities in epilepsy. These techniques permit accurate spatial correlation between intracranial EEG activity and SPECT perfusion patterns. The techniques can also be used to evaluate the effect of the extent of EEG focus resection compared with that of SISCOM focus resection to determine which has more prognostic importance in postsurgical control of seizures. Both animal and human studies are warranted to advance our knowledge of the electrophysiology associated with the various SPECT perfusion patterns.     

Ictal electroencephalographic characteristics during electroconvulsive therapy: a review of determination and clinical relevance

OBJECTIVE: The usefulness of electroencephalogram (EEG) during electroconvulsive therapy (ECT) is not limited to the duration of seizure. The use of studying its characteristics has gained attention among specialized ECT researchers. This review attempts to put the literature in this area of ictal EEG in ECT into a practical perspective. METHODS: A systematic database search using MEDLINE and EMBASE was performed using the keywords ECT and ictal EEG. RESULTS: Manual, linear, and nonlinear methods have been used to analyze EEG obtained during ECT. Most studies have used spectral or linear methods of analysis. Studies using nonlinear have been sparse. There are 4 overlapping practical applications of analysis of EEG during ECT. First, EEG can discriminate between electrode positions and more controversially different stimulus doses. Second, EEG can predict treatment response. Postictal suppression is the measure most studied from all vantage points. Nonlinear approaches to determine EEG predictors hold promise. Third, changes in the EEG across ECT sessions may indicate threshold changes and aids more optimum dosimetry. Fourth, EEG characteristics have been incorporated into ECT clinical algorithms, but this still remains controversial, and there is a paucity of studies in this area. CONCLUSIONS: The use of ictal EEG extends beyond determining the seizure length. The study of ictal EEG has certain practical uses, which could help individualize ECT treatment if applied in routine ECT practice.     

The promise of the quantitative electroencephalogram as a predictor of antidepressant treatment outcomes in major depressive disorder.

Recent studies have shown overall accuracy rates of 72% and 88% using baseline and/or 1-week change in QEEG biomarkers to predict clinical outcome to treatment with various antidepressant medications. In some cases, findings have been replicated across academic institutions and have been studied in the context of randomized, placebo-controlled trials. Recent EEG findings are corroborated by studies that use techniques with greater spatial resolution (eg, PET, MEG) in localizing brain regions pertinent to clinical response. As such, EEG measurements increasingly are validated by other physiologic measurements that have the ability to assess deeper brain structures. Continued progress along these lines may lead to the realized promise of QEEG biomarkers as predictors of antidepressant treatment outcome in routine clinical practice. In the larger context, use of QEEG technology to predict antidepressant response in major depression may mean that more patients will achieve response and remission with less of the trial-and-error approach that currently accompanies antidepressant treatment.     

EEG and psychopharmacology.

The waking EEG bears direct relations to chemical changes in the brain induced by drugs. The waking EEG is responsive to the unique characteristics of psychoactive drugs. Their EEG signatures are predictive of their short-term behavioral effects and of their clinical efficacy. This association has led to the development of cerebral electrometry - a technique to predict a drug's clinical profile from experimental trials in normal volunteers. The technique is also useful in pharmacodynamic studies. Cerebral electrometry depends on careful control of behavioral variables, quantification of EEG effects and statistical processing of the data. The EEG-behavioral associations do not depend on a single method of quantification. Behavioral association is predicted for animal studies as well. Lacking, however, are studies in animals with adequate behavioral controls, clinical correlations of direct use to the individual patient and robust tests of this association hypothesis. The past decade has shown the utility of quantitative EEG studies and improved the methodology to a practical art. The next decade should see the techniques used by classical pharmacologists, mindful of the restraints inherent in animal models of the mental aspects of behavior.     

Amplitude-integrated EEG is useful in predicting neurodevelopmental outcome in full-term infants with hypoxic-ischemic encephalopathy: a meta-analysis

Hypoxic ischemic encephalopathy is a common cause of neurological complications resulting in chronic handicapping conditions, such as cerebral palsy. Amplitude-integrated electroencephalography (EEG) has been used in many European countries for more than a decade in the evaluation of infants with hypoxic ischemic encephalopathy but has not been widely used in the United States. The objective of this study was to evaluate the evidence supporting use of amplitude-integrated EEG as a quantitative predictor of neurodevelopmental outcome in full-term infants with hypoxic ischemic encephalopathy. To assess efficacy, the authors performed a meta-analysis of the literature evaluating the use of the amplitude-integrated EEG or cerebral function monitor in full-term infants with hypoxic ischemic encephalopathy and their neurodevelopmental outcome. A total of 8 studies were eligible for the primary meta-analysis. There was an overall sensitivity of 91% (95% CI 87-95) and a negative likelihood ratio of 0.09 (95% CI .06-.15) for amplitude-integrated EEG tracings to accurately predict poor outcome. Amplitude-integrated EEG is a valuable bedside tool for predicting long-term neurodevelopmental outcome in term infants with hypoxic ischemic encephalopathy. This information is useful in structuring communication and care plans for physicians and parents. Early assessment techniques such as amplitude-integrated EEG provide objective means for determining inclusion in clinical studies evaluating therapies for hypoxic ischemic encephalopathy and for predicting which patients are most likely to respond to treatment.     

Hemimegalencephaly: Clinical, EEG, neuroimaging, and IMP-SPECT correlation

Iofetamine-single photon emission computed tomography (IMP-SPECT) was performed on 2 girls ( and 6 years of age) with histories of intractable seizures, developmental delay, and unilateral hemiparesis secondary to hemimegalencephaly. Electroencephalography (EEG) revealed frequent focal discharges in 1 patient, while a nearly continuous burst suppression pattern over the malformed hemisphere was recorded in the other. IMP-SPECT demonstrated a good correlation with neuroimaging studies. In spite of the different EEG patterns, which had been proposed to predict contrasting clinical outcomes, both IMP-SPECT scans disclosed a similar decrease in tracer uptake in the malformed hemisphere. These results are consistent with the pattern of decreased tracer uptake found in other interictal studies of focal seizures without cerebral malformations. In view of recent recommendations for hemispherectomy in these patients, we suggest that the IMP-SPECT scan be used to compliment EEG as a method to define the extent of abnormality which may be more relevant to long-term prognosis than EEG alone.     

Utility of EEG in delirium: past views and current practice.

The EEG is a useful and, at times, an essential test in the evaluation of delirium. In most patients with delirium, the EEG will show diffuse slowing and thus is helpful in differentiating organic etiologies from functional, psychiatric disorders. The degree of the EEG changes correlates with the severity of the encephalopathy so that the EEG may be used to help monitor therapy. In some delirious patients, the EEG may indicate whether the patient is suffering from focal, rather than global, impairment. Furthermore, the EEG is the only test that can identify an ongoing epileptic state (e.g., nonconvulsive status epilepticus) as being responsible for the clinical picture of confusion. Other electrophysiological tests that may prove helpful in the evaluation of delirium, such as computerized EEG spectral analysis, topographic brain mapping, and sleep studies, are briefly reviewed.     

EEG and pathologic findings in patients undergoing brain biopsy for suspected encephalitis.

Previous studies have suggested that EEG may be helpful in the diagnosis of herpes encephalitis (HE). To further define the value of EEG in an acutely ill, febrile, encephalopathic patient suspected as having encephalitis, we reviewed initial preoperative EEGs with the results of cerebral biopsies in 24 consecutive patients suspected of having encephalitis. Statistical analysis demonstrated that EEG patterns have only limited association with biopsy results. Since diseases which mimic encephalitis may also generate identical EEG changes, this is not an unexpected finding. EEG is useful in the evaluation and management of patients with encephalitis. However, the absence of specific wave forms or focal EEG abnormalities in the proper clinical setting should not deter consideration of HE or delay treatment.     

Bedeutung des EEG in der Epilepsiediagnostik

The electroencephalogram (EEG) is a specific diagnostic method for the evaluation of patients with epilepsies. Interictal epileptiform discharges (IED) recorded in the seizure interval have a high association with the clinical diagnosis of epilepsy. IEDs have to be differentiated from normal variants that resemble IEDs. The EEG may help in the localization of the epileptogenic zone and in the syndrome classification, which is important for therapy and prognosis.     

Electroencephalography/functional MRI in human epilepsy: what it currently can and cannot do

PURPOSE OF REVIEW: Simultaneous recording of electroencephalogram and functional MRI is being increasingly applied to the investigation of normal cerebral processes and disorders, particularly epilepsies. We will summarize recent epilepsy-related studies and appraise the clinical and scientific value of EEG/fMRI. RECENT FINDINGS: Interictal and ictal EEG/fMRI can provide helpful information in the presurgical evaluation of epilepsy. At present, EEG/fMRI cannot supercede any of the current methods because validation studies are lacking, informative results are only obtained in some patients, and haemodynamic activation and deactivation patterns are not always of localizing value. EEG/fMRI data often identify distributed brain areas and can help to generate concepts of epileptogenic networks both in individual patients and groups with particular epilepsy syndromes. SUMMARY: Clinically, EEG/fMRI studies may influence further investigations such as more detailed structural imaging or the planning of intracranial electrophysiological studies by generating hypotheses about the location of epileptic foci. Validation studies are underway to determine whether such clinical applications are appropriate. EEG/fMRI can also assess epileptogenic networks and changes in brain state, leading to a new dimension of understanding of dynamic cerebral processes in health and disease.     

Controversies in neurophysiology. MEG is superior to EEG in localization of interictal epileptiform activity: Pro.

Both EEG and magnetoencephalography (MEG), with a time resolution of 1 ms or less, provide unique neurophysiologic data not obtainable by other neuroimaging techniques. MEG and EEG have often been compared to each other now although the two are complementary. Now that MEG has emerged as a mature clinical technology, it is worthwhile to compare the relative strengths of each for the localization of interictal epileptiform activity and to describe the strengths of MEG relative to EEG in the localization of interictal epileptiform activity. The sources of MEG and EEG signals will first be reviewed. Issues relevant to solving the forward problem and the inverse problem in MEG and EEG will be addressed followed by a comparison of research concerning the detection and localization of interictal epileptiform activity by MEG and EEG. The emphasis will be upon techniques and software routinely used in clinical applications but some emerging areas of MEG research which are entering clinical practice will also be reviewed. SIGNIFICANCE: MEG is a new noninvasive neurophysiologic technique which provides unique information for the clinical evaluation of patients with epilepsy, revealing aspects of neuronal function that previously could only be obtained by invasive EEG monitoring, and giving a new window for research of neuronal activity.