Multifocal periodic lateralized epileptiform discharges (PLEDs): EEG features and clinical correlations

Clinical and diagnostic characteristics of Hashimoto's encephalopathy: a single-center, retrospective study

BACKGROUND AND PURPOSE

Diagnosing Hashimoto's encephalopathy (HE) is challenging. In contrast to other types of autoimmune encephalitis, HE shows an excellent response to steroid treatment. We aimed to investigate the rates of antithyroid antibodies (ATAs) and probable HE in patients with unexplained mental dysfunction and compare the clinical characteristics between the good- and poor-outcome groups.

METHODS

We retrospectively reviewed the medical records and electroencephalography (EEG) and neuroimaging findings of patients admitted to the Department of Neurology of our hospital from March 1, 2006, to February 28, 2023. Using our proposed diagnostic criteria for probable HE, we compared the clinical characteristics between the good- and poor-outcome groups. We also investigated the rates of ATA positivity and probable HE.

RESULTS

In total, 198 patients exhibited altered mentation, rapidly progressive cognitive decline, or myoclonus. ATA tests were performed on 86 patients, and the detection rates of ATAs and probable HE were 29.1% and 25.6%, respectively. Of the 22 patients enrolled, the good- and poor-outcome groups comprised 19 and 3 patients, respectively. Clinical seizures occurred in seven patients. Nonconvulsive status epilepticus on EEG was observed in six patients, all of whom were intractable to antiepileptic drugs. Nineteen of 21 patients (90.5%) treated with immunosuppressants showed good outcomes.

CONCLUSIONS

HE is a rare clinical disorder, but not as rare as previously thought. When HE is suspected, steroids should be considered the first-line treatment. Early diagnosis and adequate treatment are critical to achieve good outcomes in HE.

Electroencephalogram patterns in critical care: A primer for acute care doctors

Electroencephalograms are commonly ordered by acute care doctors but not always understood. Other reviews have covered when and how to perform electroencephalograms. This primer has a different, unique, and complementary goal. We review basic electroencephalogram interpretation and terminology for nonexperts. Our goal is to encourage common understanding, facilitate inter specialty collaboration, dispel common misunderstandings, and inform the current and future use of this precious resource. This primer is categorically not to replace the expert neurologist or technician. Quite the contrary, it should help explain how nuanced electroencephalogram can be, and why indiscriminate electroencephalogram is inappropriate. Some might argue not to teach nonexperts lest they overestimate their abilities or reach. We humbly submit that it is even more inappropriate to not know the basics of a test that is ordered frequently and resource intensive. We cover the characteristics of the "normal" electroencephalogram, electroencephalogram slowing, periodic epileptiform discharges (and its subtypes), burst suppression, and electrographic seizures (and its subtypes). Alongside characteristic electroencephalogram findings, we provide clinical pearls. These should further explain what the reporter is communicating and whether additional testing is beneficial. Along with teaching the basics and whetting the appetite of the general clinician, this resource could increase mutual understanding and mutual appreciation between those who order electroencephalograms and those who interpret them. While there is more to electroencephalogram than can be delivered via a single concise primer, it offers a multidisciplinary starting point for those interested in the present and future of this commonly ordered test.

Non-Convulsive Status Epileptics Presenting with Periodic Lateralized Epileptiform Discharges and Coma after Cerebral Hemorrhage: A Case Report

Background

Non-convulsive status epileptics (NCSE) is a common neurological emergency necessitating rapid assessment and management, but is often underdiagnosed as it lacks specific electroencephalographic features. The diagnostic value of periodic lateralized epileptiform discharges (PLEDs) in NCSE is still unclear. Herein, we reported a case with NCSE manifesting as PLEDs and coma.

Case Report

A 62-year-old man presented with epileptic seizures. Based on clinical and radiological profiles, he was diagnosed with frontal hemorrhage, coma, and NCSE. An electroencephalogram (EEG) revealed PLEDs. A combined antiepileptic regimen was initiated and, over a follow-up period of 2 months, a favorable outcome was achieved.

Conclusion

EEG may help identify potential NCSE in comatose patients, and PLEDs can be an atypical manifestation of NCSE, which can be effectively treated with antiepileptic drugs. The emphasis in NCSE is on early identification and individualized therapeutic regimens.

Etiology and Clinical Impact of Interictal Periodic Discharges on the Routine Outpatient Scalp EEG

PURPOSE

Periodic discharges (PDs) are common in acute structural or metabolic brain lesions, but their occurrence during follow-up of epileptic patients in an outpatient setting is rare. Aim of this article was to study whether PDs on the routine outpatient scalp EEG of patients with epilepsy, as compared with nonperiodic epileptiform discharges, are associated with drug refractoriness and the decompensation of epilepsy and particular etiologies.

METHODS

A retrospective case-control study. EEG reports were screened for PDs and their variants. The inclusion criteria were as follows: a diagnosis of epilepsy, epileptogenic lesion on imaging, or a normal 3-T MRI. Inpatient EEGs or EEGs performed in patients with acute cerebral lesions were excluded. Age- and sex-matched controls presenting with other epileptiform EEG abnormalities were selected, and similar selection criteria were applied.

RESULTS

Forty-one patients with PDs and 82 controls were selected. There were no significant differences between the cases and controls in the rates of epilepsy decompensation at the time of EEG collection or drug refractoriness. Stroke, hippocampal sclerosis, and malformations of cortical development were the most frequent etiologies, without significant differences between the groups.

CONCLUSIONS

By performing a case-control study, the authors have shown that PDs are not a marker of epilepsy decompensation and drug refractoriness and that the finding of PDs is not suggestive of particular epilepsy etiologies, when compared with other epileptiform abnormalities.

Inhibiting Epileptiform Activity in Cognitive Disorders: Possibilities for a Novel Therapeutic Approach

Cognitive impairment is a common and seriously debilitating symptom of various mental and neurological disorders including autism, attention deficit hyperactivity disorder, multiple sclerosis, epilepsy, and neurodegenerative diseases, like Alzheimer's disease. In these conditions, high prevalence of epileptiform activity emerges as a common pathophysiological hallmark. Growing body of evidence suggests that this discrete but abnormal activity might have a long-term negative impact on cognitive performance due to neuronal circuitries' remodeling, altered sleep structure, pathological hippocampo-cortical coupling, and even progressive neuronal loss. In animal models, epileptiform activity was shown to enhance the formation of pathological amyloid and tau proteins that in turn trigger network hyperexcitability. Abolishing epileptiform discharges might slow down the cognitive deterioration. These findings might provide basis for therapeutic use of antiepileptic drugs in neurodegenerative cognitive disorders. The aim of our review is to describe the data on the prevalence of epileptiform activity in various cognitive disorders, to summarize the current knowledge of the mechanisms of epileptic activity in relation to cognitive impairment, and to explore the utility of antiepileptic drugs in the therapy of cognitive disorders. We also propose future directions for drug development and novel therapeutic interventions targeting epileptiform discharges in these disorders.

Electroencephalogram (EEG) in COVID-19: A systematic retrospective study

OBJECTIVES

Although rare, neurological manifestations in SARS-CoV-2 infection are increasingly being reported. We conducted a retrospective systematic study to describe the electroencephalography (EEG) characteristics in this disease, looking for specific patterns.

METHODS

EEGs performed in patients with positive PCR for SARS-CoV-2 between 25/03/2020 and 06/05/2020 in the University Hospital of Bicêtre were independently reviewed by two experienced neurologists. We used the American Clinical Neurophysiology Society's terminology for the description of abnormal patterns. EEGs were classified into five categories, from normal to critically altered. Interobserver reliability was calculated using Cohen's kappa coefficient. Medical records were reviewed to extract demographics, clinical, imaging and biological data.

RESULTS

Forty EEGs were reviewed in 36 COVID-19 patients, 18 in intensive care units (ICU) and 22 in medicine units. The main indications were confusion or fluctuating alertness for 23 (57.5%) and delayed awakening after stopping sedation in ICU in six (15%). EEGs were normal to mildly altered in 23 (57.5%) contrary to the 42.5% where EEG alterations were moderate in four (10%), severe in eight (20%) and critical in five (12.5%). Generalized periodic discharges (GPDs), multifocal periodic discharges (MPDs) or rhythmic delta activity (RDA) were found in 13 recordings (32.5%). EEG alterations were not stereotyped or specific. They could be related to an underlying morbid status, except for three ICU patients with unexplained encephalopathic features.

CONCLUSION

In this first systematic analysis of COVID-19 patients who underwent EEG, over half of them presented a normal recording pattern. EEG alterations were not different from those encountered in other pathological conditions.

Definition and Classification of Periodic and Rhythmic Patterns

The growing use of continuous video-EEG recording in the inpatient setting, in particular in patients with varying degrees of encephalopathy, has yielded a window to the brain with an excellent temporal resolution. This increasingly available tool has become more than an instrument to detect nonconvulsive seizures (its primary use), and clinical indications span from ischemia detection in acute brain injuries, neuroprognostication of comatose patients, to monitoring the degree of encephalopathy. In this context, abnormal findings such as periodic discharges and rhythmic delta activity were increasingly recognized; however, significant subjectivity remained in the interpretation of these findings pertaining to key features regarding their spatial involvement, prevalence of occurrence, duration, associated morphologic features, and behavior. In 2005, the American Clinical Neurophysiology Society proposed standardized definitions and classification of electroencephalographic rhythmic and periodic patterns. This was subsequently revised in 2011 and in 2012 and is now being used by centers worldwide, with the final version published in early 2013 as an official guideline of the ACNS. The resulting uniform terminology has allowed for significant advances in the understanding of the pathophysiology, epileptogenic potential, and overall clinical implication of these patterns. Investigators across multiple institutions are now able to collaborate while exploring diagnostic and therapeutic algorithms to these patterns, an effort that may soon provide definitive evidence guiding treating clinicians on the management of these patients.

Lateralized Periodic Discharges: A Literature Review

The purpose of this article is to provide a comprehensive review of the literature about a particular EEG pattern, lateralized periodic discharges (LPDs), or periodic lateralized epileptiform discharges (PLEDs). The review will discuss the history and terminology of LPDs and provide a detailed summary of the etiologies, pathophysiology, clinical symptoms, and imaging studies related to LPDs. Current controversies about the association of LPDs with seizures and their management will be reviewed. Finally, some unanswered questions and suggestions for future research on LPDs will be discussed.

Periodic Lateralized Epileptiform Discharges can Survive Anesthesia and Result in Asymmetric Drug-induced Burst Suppression

Drug-induced burst suppression (DIBS) is bihemispheric and bisymmetric in adults and older children. However, asymmetric DIBS may occur if a pathological process is affecting one hemisphere only or both hemispheres disproportionately. The usual suspect is a destructive lesion; an irritative or epileptogenic lesion is usually not invoked to explain DIBS asymmetry. We report the case of a 66-year-old woman with new-onset seizures who was found to have a hemorrhagic cavernoma and periodic lateralized epileptiform discharges (PLEDs) in the right temporal region. After levetiracetam and before anesthetic antiepileptic drugs (AEDs) were administered, the electroencephalogram (EEG) showed continuous PLEDs over the right hemisphere with maximum voltage in the posterior temporal region. Focal electrographic seizures also occurred occasionally in the same location. Propofol resulted in bihemispheric, but not in bisymmetric, DIBS. Remnants or fragments of PLEDs that survived anesthesia increased the amplitude and complexity of the bursts in the right hemisphere leading to asymmetric DIBS. Phenytoin, lacosamide, ketamine, midazolam, and topiramate were administered at various times in the course of EEG monitoring, resulting in suppression of seizures but not of PLEDs. Ketamine and midazolam reduced the rate, amplitude, and complexity of PLEDs but only after producing substantial attenuation of all burst components. When all anesthetics were discontinued, the EEG reverted to the original preanesthesia pattern with continuous non-fragmented PLEDs. The fact that PLEDs can survive anesthesia and affect DIBS symmetry is a testament to the robustness of the neurodynamic processes underlying PLEDs.

Ictal-interictal continuum: A proposed treatment algorithm

The ictal-interictal continuum (IIC) is characterized by periodic and/or rhythmic EEG patterns that occur with relative high frequency in critically ill patients. Several studies have reported that some patterns seen within the continuum are independently associated with poor outcome. However there is no consensus regarding when to treat them or how aggressive treatment should be. In this review we examine peer-reviewed original scientific articles, guidelines and reviews indexed in PubMed and summarize current knowledge related to the ictal-interictal continuum. A treatment algorithm to guide management of critically ill patients with EEG patterns that fall along the IIC is proposed. The algorithm-based on best current practice in adults-takes into account associated clinical events, risk factors for developing seizures, response to medication trials and biomarkers of neuronal injury.

Which EEG patterns in coma are nonconvulsive status epilepticus?

Nonconvulsive status epilepticus (NCSE) is common in patients with coma with a prevalence between 5% and 48%. Patients in deep coma may exhibit epileptiform EEG patterns, such as generalized periodic spikes, and there is an ongoing debate about the relationship of these patterns and NCSE. The purposes of this review are (i) to discuss the various EEG patterns found in coma, its fluctuations, and transitions and (ii) to propose modified criteria for NCSE in coma. Classical coma patterns such as diffuse polymorphic delta activity, spindle coma, alpha/theta coma, low output voltage, or burst suppression do not reflect NCSE. Any ictal patterns with a typical spatiotemporal evolution or epileptiform discharges faster than 2.5 Hz in a comatose patient reflect nonconvulsive seizures or NCSE and should be treated. Generalized periodic diacharges or lateralized periodic discharges (GPDs/LPDs) with a frequency of less than 2.5 Hz or rhythmic discharges (RDs) faster than 0.5 Hz are the borderland of NCSE in coma. In these cases, at least one of the additional criteria is needed to diagnose NCSE (a) subtle clinical ictal phenomena, (b) typical spatiotemporal evolution, or (c) response to antiepileptic drug treatment. There is currently no consensus about how long these patterns must be present to qualify for NCSE, and the distinction from nonconvulsive seizures in patients with critical illness or in comatose patients seems arbitrary. The Salzburg Consensus Criteria for NCSE [1] have been modified according to the Standardized Terminology of the American Clinical Neurophysiology Society [2] and validated in three different cohorts, with a sensitivity of 97.2%, a specificity of 95.9%, and a diagnostic accuracy of 96.3% in patients with clinical signs of NCSE. Their diagnostic utility in different cohorts with patients in deep coma has to be studied in the future. This article is part of a Special Issue entitled "Status Epilepticus".

PLEDS : corrélations cliniques

Objective:

We reviewed our experience in 96 consecutive patients exhibiting periodic lateralized epileptiform discharges (PLEDs) on EEG.

Methods:

EEG reports from January 1, 1999 to September 30, 2006 were screened for the term ‘PLEDs’ and its variants. A retrospective chart review, including examination of neuroimaging and other investigations, was conducted on each patient identified.

Results:

Acute stroke, tumor and central nervous system infection were the most common etiologies, accounting for 26%, 12% and 12% of cases respectively. Acute hemorrhage and traumatic brain injury combined accounted for another 12%. Previously unreported etiologies included posterior reversible encephalopathy syndrome (PRES), familial hemiplegic migraine and cerebral amyloidosis. There were 9 cases of chronic PLEDs attributable to underlying cortical dysplasia or severe remote cerebral injury, all with an accompanying partial seizure disorder. A prominent role for alcohol withdrawal was noted, and in 6 cases was the sole etiological factor. Fever was present as a potential contributing factor in 40% of cases, and significant metabolic abnormalities in 35%. Seizure activity occurred in 85% of patients overall, but in 100% of patients with PLEDs Plus and BiPLEDs Plus. The overall mortality rate was 27%. Mortality among patients with BiPLEDs however was almost twice that, at 52%.

Conclusions:

This case series demonstrates the wide variety of potential PLED etiologies. It also emphasizes that despite advances in neurocritical care, the morbidity and mortality associated with PLEDs has changed little since their recognition four decades ago.

Preliminary Findings of Single- and Multifocused Epileptiform Discharges in Nonepileptic Psychiatric Patients

Epileptiform discharges (EDs) in nonepileptic populations remain controversial as to their role in psychopathology. Previous studies have unsuccessfully attempted to correlate specific waveforms of EDs, defined by duration and morphology, with broad diagnostic categories such as depression and anxiety. These diagnostic categories often include heterogeneous patient populations, with potentially divergent biological underpinnings of clinical presentation. This study examined epileptiform activities as a single phenomenon, identifying the relationships between distribution patterns of EDs and endorsement of clinical symptoms across affective, cognitive, and somatic domains. In a sample of 71 nonepileptic psychiatric patients, those with EDs appearing in homologous electrode pairs endorsed significantly fewer symptoms related to affective deregulation. These patients were also significantly less likely to endorse a history of severe symptomatology, including suicidal ideation/previous attempt, self-injurious behavior, psychoses or dissociation, and previous psychiatric hospitalization. Conversely, patients with isolated EDs focused to a single brain region endorsed greater affective deregulation and severe clinical symptoms. These findings offer new possibilities regarding the potentially protective role that EDs may play when distributed across hemispheres, particularly in light of recent theories exploring functional connectivity of neuronal networks.

Periodic Epileptiform Discharges Clarified for the Nonneurologist Intensivist: Clinical Implications and Current Management

Periodic epileptiform discharges (PEDs) are frequently encountered during continuous electroencephalography monitoring in the intensive care unit. Their implications and management are variable and highly dependent on the clinical context. This article is intended for the nonneurologist intensivist, reviews basic terminology and clinical implications (including causes, prognosis, and association with seizures), and suggests an approach to management. Several case vignettes are included to illustrate the clinical variability associated with PEDs.

Nonconvulsive status epilepticus and coma

Nonconvulsive status epilepticus (NCSE) in a comatose patient cannot be diagnosed without electroencephalography (EEG). In many advanced coma stages, the EEG exhibits continuous or periodic EEG abnormalities, but their causal role in coma remains unclear in many cases. To date there is no consensus on whether to treat NCSE in a comatose patient in order to improve the outcome or to retract from treatment, as these EEG patterns might reflect the end stages of a dying brain. On the basis of EEG, NCSE in comatose patients may be classified as generalized or lateralized. This review aims to summarize the ongoing debate of NCSE and coma and to critically reassess the available literature on coma with epileptiform EEG pattern and its prognostic and therapeutic implications. The authors suggest distinguishing NCSE proper and comatose NCSE, which includes coma with continuous lateralized discharges or generalized epileptiform discharges (coma-LED, coma-GED). Although NCSE proper is accompanied by clinical symptoms suggestive of status epilepticus and mild impairment of consciousness, such as in absence status or complex focal status epilepticus, coma-LED and coma-GED represent deep coma of various etiology without any clinical motor signs of status epilepticus but with characteristic epileptiform EEG pattern. Hence coma-LED and coma-GED can be diagnosed with EEG only. Subtle or stuporous status epilepticus and epilepsia partialis continua-like symptoms in severe acute central nervous system (CNS) disorders represent the borderland in this biologic continuum between NCSE proper and comatose NCSE (coma-LED/GED). This pragmatic differentiation could act as a starting point to solve terminologic and factual confusion.

Periictal magnetic resonance imaging in status epilepticus

PURPOSE

To determine the changes of magnetic resonance imaging (MRI) during the periictal phase in status epilepticus (SE).

PATIENTS AND METHODS

We identified 15 patients diagnosed of status epilepticus with corresponding MRI changes, including 11 patients with generalized convulsive status epilepticus (GCSE), 2 with complex partial status epilepticus (CPSE), and 2 with simple partial status epilepticus (SPSE). All MRI changes, corresponding electroencephalogram, and prognosis were evaluated.

RESULTS

Regional cortical lesions were observed on MRI, including restricted diffusion in diffusion-weighted images (DWIs) (11 out of 15) and hyperintense signal change in fluid-attenuated inversion recovery (FLAIR) images (12 out of 15) with hypervascularity and parenchymal swelling. The remote lesions included crossed cerebellar diaschisis (3 patients), ipsilateral thalamic lesion (4 patients), and basal ganglia lesions (3 patients). Although the periictal MRI changes were usually reversible, irreversible changes were also found, especially in GCSE, such as focal brain atrophy, cortical laminar necrosis, and mesial temporal sclerosis. GCSE patients with periodic epileptic form discharges had higher possibilities of widespread MRI abnormalities and poor prognosis in the future.

CONCLUSIONS

In this study, DWIs and FLAIR images were proved useful in determining the extent and severity of early neuronal damage caused by epileptic discharges in SE patients. Seizure-induced long-term injuries were also observed in the follow-up MRI.

Neuroimaging and Neurophysiology of Periodic Lateralized Epileptiform Discharges: Observations and Hypotheses

PURPOSE

We assessed neuroimaging lesion type and distribution in patients with periodic lateralized epileptiform discharges (PLEDs), with a view to identifying electrographic differences between PLEDs associated with differing lesion locations. Our observations led us to consider a conceptual synthesis between PLEDs and periodic complexes (PCs).

METHODS

Retrospective review of acute neuroimaging results (CT/MRI) on patients identified to have EEG PLEDs, for the period 1999-2003 (n=106). Blinded classification of original EEG recordings.

RESULTS

Neuroimaging abnormalities were classified as acute or chronic cortical, or acute or chronic subcortical. Seven out of 106 scans were classified nonlesional. Overall approximately 70% of scans had cortical abnormalities, whether acute or chronic; approximately 23% had subcortical abnormalities. "Cortical" PLEDs were significantly longer in duration (p<0.05) and more variable in morphology (p<0.01) than "subcortical" PLEDs.

CONCLUSIONS

Structural brain disease commonly, but not invariably, underlies PLEDs; lesion type is spatiotemporally variable. Cortical and subcortical PLEDs have distinct EEG signatures. There is evidence that these may relate to mechanisms for other pathological large-scale oscillatory brain synchronies (e.g., PCs).

Prognostic significance of continuous EEG monitoring in patients with poor-grade subarachnoid hemorrhage

INTRODUCTION

Predicting outcome in patients with poor-grade subarachnoid hemorrhage (SAH) may help guide therapy and assist in family discussions. The objective of this study was to determine if continuous electroencephalogram (cEEG) monitoring results are predictive of 3-month outcome in critically ill patients with SAH.

METHODS

We prospectively studied 756 patients with SAH over a 7-year period. Functional outcome was assessed at 3 months with the modified Rankin Scale (mRS). Patients that underwent cEEG monitoring were retrospectively identified and EEG findings were collected. Multivariate logistic regression analysis was performed to identify EEG findings associated with poor outcome, defined as mRS 4 to 6 (dead or moderately to severely disabled).

RESULTS

In 116 patients with SAH, cEEG monitoring and 3-month mRS were available. Of these patients, 88% had a Hunt & Hess grade of 3 or worse on admission. After controlling for age, Hunt & Hess grade, and presence of intraventricular hemorrhage on admission CT scan, poor outcome was associated with the absence of sleep architecture (80 versus 47%; odds ratio [OR] 4.3, 95%-confidence interval [CI] 1.1-17.2) and the presence of periodic lateralized epileptiform discharges (PLEDS) (91 versus 66% OR 18.8, 95%-CI 1.6-214.6). In addition, outcome was poor in all patients with absent EEG reactivity (n = 8), generalized periodic epileptiform discharges (n = 12), or bilateral independent PLEDs (n = 5), and in 92% (11 of 12) of patients with nonconvulsive status epilepticus.

CONCLUSIONS

cEEG monitoring provides independent prognostic information in patients with poor-grade SAH, even after controlling for clinical and radiological findings. Unfavorable findings include periodic epileptiform discharges, electrographic status epilepticus, and the absence of sleep architecture.

Rapid recovery from coma with multifocal PLEDs in a patient with severe dementia and transient hypoxemia

We report a patient with severe dementia who acutely developed transient coma following possible acute anoxic encephalopathy, and presented multifocal periodic lateralized epileptiform discharges (PLEDs) on EEG, who had a good recovery from the acute state. Two EEGs were recorded from this patient. In the first EEG taken immediately after admission, multifocal PLEDs were prominent, and the background activity consisted of low voltage, continuous and irregular theta activity (4-6 Hz). The patient recovered from coma (GCS-3) to the conscious state (GCS-15) within 14 hours and was not associated with newly developed focal or global neurological deficits except for stable severe dementia which had developed in the previous several years. Another EEG taken 5 days later showed disappearance of multifocal PLEDs. Transient appearance of multifocal PLEDs might represent at least the transient, vulnerability associated with underlying dementia in this particular patient. We concluded that multifocal PLEDs do not always indicate a poor outcome in patients with possible acute anoxic encephalopathy, and rapid diagnosis and appropriate treatment should be done even if the initial EEG shows multifocal PLEDs.

Convulsant and anticonvulsant effects on spontaneous CA3 population bursts

This paper analyzes the effects of a convulsant and an anticonvulsant manipulation on spontaneous bursts in CA3 pyramidal cells in the in vitro slice preparation under conditions of low (3.3 mM [K(+)](o)) and high (8.5 mM [K(+)](o)) burst probability. When burst probability was low, the anticonvulsant, pentobarbital, produced the anticipated effects: the burst duration decreased and interburst interval increased. However, when burst probability was high, both anticonvulsant and convulsant manipulations decreased the interburst interval and the burst duration. To reconcile these findings, we utilized a model in which CA3 burst duration is limited by activity-dependent depression of CA3 excitatory recurrent collateral synapses and the interburst interval is determined by the time required to recover from this depression. We defined the burst end threshold as the level of synaptic depression at which bursts terminate, and the burst start threshold as the level of synaptic depression at which burst initiation is possible. Synapses were considered to oscillate between these thresholds. When average burst duration and interburst interval data were fit using this model, the paradoxically similar effects of the convulsant and anticonvulsant manipulations could be quantitatively interpreted. The convulsant maneuver decreased both the burst start and end thresholds. The start threshold decreased more than the end threshold, so that the thresholds were closer together. This decreased the time needed to transition from one threshold to the other, i.e., the interburst interval and burst duration. The anticonvulsant manipulation primarily increased the burst end threshold. This also decreased the difference between thresholds, decreasing both interburst interval and burst duration. This model resolves the paradoxical proconvulsant effects of pentobarbital in the CA3 preparation and provides insights into the effects of anticonvulsants on epileptiform discharges in the human EEG.

Role and limitations of routine and ambulatory scalp electroencephalography in diagnosing and managing seizures

The scalp electroencephalogram (EEG) is the cornerstone in the diagnosis and treatment of seizure disorders. The EEG, with its excellent temporal resolution, provides a direct measurement of cortical electrophysiology, revealing, for example, the presence of interictal epileptiform discharges that identify regions of an epileptogenic brain. We define the EEG characteristics of focal and generalized epileptiform discharges and provide evidence for their varying diagnostic importance in different patient populations. Identification of nonepileptiform EEG transients, such as wicket waves, small sharp spikes,rhythmic temporal theta activity, and 14- and 6-Hz positive bursts, that can be confused for epileptiform transients is emphasized. A final point is that the clinician must interpret EEG findings within the overall clinical context.

BIPLEDs in akinetic mutism caused by bilateral anterior cerebral artery infarction

INTRODUCTION

Akinetic mutism is described as a result of many disorders. Bilateral infarction of the anterior cerebral artery (ACA) territory is reported rarely, however, often leading to akinetic mutism.

CASE REPORT

We report a 70 year-old man with akinetic mutism due to bilateral ACA infarction. Electroencephalography, 24h after admission, showed bilateral independent periodic lateralized epileptiform discharges (BIPLEDs) in the frontal region and diffuse theta and polymorphic delta activity.

DISCUSSION

Postanoxic encephalopathy, central nervous system infection and chronic seizure disorders are the major causes of BIPLEDs. However, BIPLEDs may occur in bilateral ACA territory infarction.