EEG Interictal Epileptiform Discharges Research Articles

Optimized set of criteria for defining interictal epileptiform EEG discharges

ObjectiveTo find and validate the optimal combination of criteria that define interictal epileptiform EEG discharges (IEDs). Our target was a specificity over 95%, to avoid over-reading in clinical EEG. MethodsWe constructed 63 combinations of the six criteria from the operational definition of IEDs, recently issued in the EEG-glossary of the International Federation of Clinical Neurophysiology (IFCN). The diagnostic gold standard was derived from video-EEG recordings. In a testing EEG dataset from 100 patients, we selected the best performing combinations of criteria and then we validated them in an independent dataset from 70 patients. We compared their performance with subjective, expert-scorings and we determined inter-rater agreement (IRA). ResultsWithout using criteria, the specificity of expert-scorings was lower than the pre-defined threshold (86%). The best performing combination of criteria was the following: waves with spiky morphology, followed by a slow-afterwave and voltage map suggesting a source in the brain. In the validation dataset this achieved a specificity of 97% and a sensitivity of 89%. IRA was substantial. ConclusionsThe optimized set of criteria for defining IEDs has high accuracy and IRA. SignificanceUsing these criteria will contribute to decreasing over-reading of EEG and avoid misdiagnosis of epilepsy.

Criteria for defining interictal epileptiform discharges in EEG: A clinical validation study.

ObjectiveTo define and validate criteria for accurate identification of EEG interictal epileptiform discharges (IEDs) using (1) the 6 sensor space criteria proposed by the International Federation of Clinical Neurophysiology (IFCN) and (2) a novel source space method. Criteria yielding high specificity are needed because EEG over-reading is a common cause of epilepsy misdiagnosis.MethodsSeven raters reviewed EEG sharp transients from 100 patients with and without epilepsy (diagnosed definitively by video-EEG recording of habitual events). Raters reviewed the transients, randomized, and classified them as epileptiform or nonepileptiform in 3 separate rounds: in 2, EEG was reviewed in sensor space (scoring the presence/absence of each IFCN criterion for each transient or classifying unrestricted by criteria [expert scoring]); in the other, review and classification were performed in source space.ResultsCutoff values of 4 and 5 criteria in sensor space and analysis in source space provided high accuracy (91%, 88%, and 90%, respectively), similar to expert scoring (92%). Two methods had specificity exceeding the desired threshold of 95%: using 5 IFCN criteria as cutoff and analysis in source space (both 95.65%); the sensitivity of these methods was 81.48% and 85.19%, respectively.ConclusionsThe presence of 5 IFCN criteria in sensor space and analysis in source space are optimal for clinical implementation. By extracting these objective features, diagnostic accuracy similar to expert scorings is achieved.Classification of evidenceThis study provides Class III evidence that IFCN criteria in sensor space and analysis in source space have high specificity (>95%) and sensitivity (81%–85%) for identification of IEDs.

Effect of interictal epileptiform EEG discharges on cognitive functions in epileptic children

Background: Epilepsy is a chronic disorder of the brain that affects people of all ages Neuropsychological impairment is an important comorbidity of chronic epilepsy in the majority of children with epilepsy. interictal epileptiform EEG discharges may present as a complicating factor in spite of being seizure free. In a group of children with interictal EEG discharges there is sudden and unexpected decline of school performance as the first symptom of epilepsy. Consequently, accumulating cognitive impairment, and even a decline in IQ scores, is reported in epileptic children with frequent episodes with epileptiform EEG discharges. Aim of the Work: To evaluate the possible relationship between interictal EEG discharge and cognitive function in a sample of Egyptian epileptic children. Patients and Methods: The ethical approval was obtained from the Hospital Ethical Research Committee. Each patient and/or parents entering the study signed an informed consent. This study was conducted on 140 children selected from Epilepsy Outpatient Clinic of Al-Azhar University Hospitals during a period of two years starting from June 2016 untill June 2018. A specialized pediatric neurology sheet was taken. EEG and cognitive assessment of epileptic patients with and without epileptiform EEG discharges using Stanford-Binet intelligence scale and P300 by ERP were performed to each patient two times 3 months in between. Results: we found that patients with frequent IEDs had high mean P300 latency and low IQ when compared to patients with infrequent and normal EEG examination. In addition, the mean p300 latency significantly reduced with rising in IQ (more improvement in cognitive function) after disappearance of IED in some patients. Conclusion: Interictal epileptiform EEG discharge had an additional effect on cognitive function especially if generalized and of high frequency. This effect might be often underestimated and might accumulate, and have a severe cognitive impact. So, treatment of epileptic patients should put in concern reduction or even treatment of IEDs as controlling of these IED lead to improvement of cognition.

Effect of interictal epileptiform EEG discharges on cognitive functions in epileptic children

Background: Epilepsy is a chronic disorder of the brain that affects people of all ages Neuropsychological impairment is an important comorbidity of chronic epilepsy in the majority of children with epilepsy. interictal epileptiform EEG discharges may present as a complicating factor in spite of being seizure free. In a group of children with interictal EEG discharges there is sudden and unexpected decline of school performance as the first symptom of epilepsy. Consequently, accumulating cognitive impairment, and even a decline in IQ scores, is reported in epileptic children with frequent episodes with epileptiform EEG discharges. Aim of the Work: To evaluate the possible relationship between interictal EEG discharge and cognitive function in a sample of Egyptian epileptic children. Patients and Methods: The ethical approval was obtained from the Hospital Ethical Research Committee. Each patient and/or parents entering the study signed an informed consent. This study was conducted on 140 children selected from Epilepsy Outpatient Clinic of Al-Azhar University Hospitals during a period of two years starting from June 2016 untill June 2018. A specialized pediatric neurology sheet was taken. EEG and cognitive assessment of epileptic patients with and without epileptiform EEG discharges using Stanford-Binet intelligence scale and P300 by ERP were performed to each patient two times 3 months in between. Results: we found that patients with frequent IEDs had high mean P300 latency and low IQ when compared to patients with infrequent and normal EEG examination. In addition, the mean p300 latency significantly reduced with rising in IQ (more improvement in cognitive function) after disappearance of IED in some patients. Conclusion: Interictal epileptiform EEG discharge had an additional effect on cognitive function especially if generalized and of high frequency. This effect might be often underestimated and might accumulate, and have a severe cognitive impact. So, treatment of epileptic patients should put in concern reduction or even treatment of IEDs as controlling of these IED lead to improvement of cognition.

Long-term outcome characteristics in mesial temporal lobe epilepsy with and without associated cortical dysplasia

ObjectThe intention of our study was to identify predictive characteristics for long-term seizure control and running down phenomenon after surgical treatment of pharmacoresistant mesiotemporal lobe epilepsy (mTLE) with and without associated cortical dysplasia. Materials and methodsOur study comprises a consecutive series of 458 patients who underwent surgical treatment for intractable mTLE at the Epilepsy Center Freiburg. Data evaluated included semiology, duration and frequency of seizures, results of presurgical diagnostics including video-EEG monitoring, MRI, PET and SPECT as well as postoperative seizure outcome. Results were evaluated forming two groups: Group A consisted of isolated mesiotemporal lesions. Group B comprised patients with mTLE and additional focal cortical dysplasia (FCD). Statistical evaluation was based on the Kaplan Meier survival analysis, using log-rank-tests and a multivariate regression model. Postoperative running down phenomenon was defined as seizure freedom after a period of gradual reduction of postoperative seizure frequency. This was compared to patients with ongoing epilepsy. ResultsComplete seizure freedom was achieved in 65.0% of investigated patients at 1year and in 56.5% at long-term follow-up of ≥5 years after surgery. Corresponding results were 64.2% and 56.8% at 1 and ≥5 years, respectively in group A and 66.4% and 56.0%, respectively in group B. Predictive for favorable postoperative outcome in the total group were younger age at surgery, shorter duration of epilepsy, absence of secondarily generalized tonic-clonic seizures (SGTCS), presence of strictly ipsilateral temporal interictal epileptiform discharges (IEDs), complete resection of the lesion as well as absence of postoperative epileptiform activity and of early postoperative seizures. In subgroup analyses, patients of group A demonstrated longer postoperative seizure-free intervals with adolescent age at surgery, short duration of epilepsy before surgery and absence of SGTCS, whereas in patients of group B ipsilateral temporal seizure onset and strictly unilateral IEDs in EEG as well as complete resection were predictors for favorable seizure outcome. Furthermore, absence of early postoperative seizures and of spikes in EEG were predictive factors for long-term seizure-freedom in both subgroups.The running down phenomenon was found in 33 (7.2%) patients. None of the parameters evaluated demonstrated significant predictive power. Only late seizure onset and neoplastic lesions showed a trend for postoperative gradual seizure reduction in multivariate analyses. ConclusionDepending on the presence or absence of focal cortical dysplasia in addition to mesiotemporal structural alterations, predictors of long-term seizure control differed regarding the relevant clinical and electrophysiological features. This is important for specific patient counseling in respective groups.

Sleep-Related Disorders in Children with Attention-Deficit Hyperactivity Disorder: Preliminary Results of a Full Sleep Assessment Study.

We present the preliminary results of a prospective case-control sleep study in children with a diagnosis of attention-deficit hyperactivity disorder (ADHD). A deep sleep assessment including sleep questionnaires, sleep habits, a video-polysomnographic recording with full high-density electroencephalography (EEG) and cardiorespiratory polygraphy, multiple sleep latency test, and 1-week actigraphic recording were performed to verify whether children with ADHD may be classified into one of the following five phenotypes: (1) hypoarousal state, resembling narcolepsy, which may be considered a "primary" form of ADHD; (2) delayed sleep onset insomnia; (3) sleep-disordered breathing; (4) restless legs syndrome and/or periodic limb movements; and (5) sleep epilepsy and/or EEG interictal epileptiform discharges. Fifteen consecutive outpatients with ADHD were recruited (two female, mean age 10.6±2.2, age range 8-13.7 years) over 6months. The narcolepsy-like sleep phenotype was observed in three children, the sleep onset insomnia phenotype was observed in one child, mild obstructive sleep apnea was observed in three children, sleep hyperkinesia and/or PLMs were observed in five children, while IEDs and or nocturnal epilepsy were observed in three children. Depending on the sleep phenotype, children received melatonin, iron supplementation, antiepileptic drugs, or stimulants. Our study further highlights the need to design an efficient sleep diagnostic algorithm for children with ADHD, thereby more accurately identifying cases in which a full sleep assessment is indicated.

Epileptic networks are strongly connected with and without the effects of interictal discharges.

Epilepsy is increasingly considered as the dysfunction of a pathologic neuronal network (epileptic network) rather than a single focal source. We aimed to assess the interactions between the regions that comprise the epileptic network and to investigate their dependence on the occurrence of interictal epileptiform discharges (IEDs). We analyzed resting state simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI) recordings in 10 patients with drug-resistant focal epilepsy with multifocal IED-related blood oxygen level-dependent (BOLD) responses and a maximum t-value in the IED field. We computed functional connectivity (FC) maps of the epileptic network using two types of seed: (1) a 10-mm diameter sphere centered in the global maximum of IED-related BOLD map, and (2) the independent component with highest correlation to the IED-related BOLD map, named epileptic component. For both approaches, we compared FC maps before and after regressing out the effect of IEDs in terms of maximum and mean t-values and percentage of map overlap. Maximum and mean FC maps t-values were significantly lower after regressing out IEDs at the group level (p < 0.01). Overlap extent was 85% ± 12% and 87% ± 12% when the seed was the 10-mm diameter sphere and the epileptic component, respectively. Regions involved in a specific epileptic network show coherent BOLD fluctuations independent of scalp EEG IEDs. FC topography and strength is largely preserved by removing the IED effect. This could represent a signature of a sustained pathologic network with contribution from epileptic activity invisible to the scalp EEG.

Strong “intrinsic” functional connectivity of epileptic networks independent of scalp interictal epileptiform EEG discharges

Objective Epileptic activity arises from dysfunction of pathological neuronal network (epileptic network). Aim: to assess maintenance of epileptic network in between IEDs occurrence. Methods We acquired simultaneous EEG-fMRI resting state in 10 drug-resistant focal epilepsy patients, having multifocal BOLD response and maximal t -value in the IED field. We compared results of functional connectivity (FC) before and after removing IEDs effect for two seed types: a 10mm-diameter sphere drawn in the BOLD map maximum and the epileptic component obtained by Indipendent component analysis. We evaluated the results in terms of mean t -value and the percentage of overlap between the FC maps. Results Mean t -value was significant lower after regressing out the IEDs at group level ( p = 0.008 for sphere; p = 0.0004 for epileptic component). Overlap extent was 85% ± 12% and 87% ± 12% for the sphere and the epileptic component, respectively. Conclusions Regions involved in a specific epileptic network show coherent oscillation independent of the occurrence of interictal activity. This could indicate the presence of epileptic activity invisible to the scalp-EEG or the presence of new and pathological resting state networks. Key message Regions involved in a specific epileptic network show functional coupling independently of the occurrence of interictal activity as revealed on scalp EEG.

Formation of paroxysmal brain activity in the liquidators of the consequences of the Chernobyl nuclear disaster

To investigate the effect of ionizing radiation on the formation of paroxysmal brain activity (PBA) in the liquidators of the consequences of the Chernobyl nuclear disaster in view of their age on the date of exposure to radiation. EEG examinations were performed in 105 liquidators of the consequences of the nuclear disaster (LCND) and 90 people without radiation anamnesis (control group). It has been determined that the formation of paroxysmal brain activity in LCND occurs 3.5 times more frequent (p<0.001) and 15-17 years earlier (p<0.001) than in the control group and mainly during the first 10 years after the exposure to radiation. The history of the exposure to ionizing radiation is associated with the increased risk of the development of convulsive PBA as focal seizures by 5.5 times (p<0.001), interictal epileptiform discharges (IED) in EEG by 3.3 times (p<0.001). Radiation effect on LCND under 30 years old increases (as compared to the control group) the risk of the formation of elevated paroxysmal brain activity by 19 times (p<0.001), convulsive epileptic seizures by 33.3 times (p<0.001), interictal epileptiform discharges in EEG by 12 times (p<0.001), asymptomatic focal epileptoid nidus in EEG by 9.3 times (p<0.001). Stimulating effect of ionizing radiation on the development of PBA related to the age on the date of exposure to radiation was found.

Electroencephalographic aspects in dogs with congenital hydrocephalus

Introduction: Congenital hydrocephalus (CH) is a common neurologic disorder in dogs defined as an increased cerebrospinal fluid volume within the cranial cavity with no any specific causes. The diagnosis of this disease is based on the clinical features and imagistic examination (ultrasonography, CT, MRI) of the brain. Electroencephalography (EEG) is the best electrodiagnostic test in trying to assess the impact of hydrocephalus on electric activity of the brain . T he aim of this study is to describe short time EEG changes in dogs with CH. Materials and Methods: EEG was performed on 6 dogs with congenital hydrocephalus under general anaesthesia with medetomidine hydrochloride 0.05 mg/kg inj. EEGs were obtained via five subdermal stainless steel needle electrodes as described by Redding (1978). In EEG recoding the parameters used were: sensitivity = 70I¼V/cm; time constant = 0.3 seconds; Hf = 70 Hz; Lf = 0.5 Hz; notch filter inserted; impedance of all electrodes < 10 kI©. The results of the present study revealed abnormalities in EEG background activity in all dogs. Focal abnormalities were seen in 5 patients (slow waves in 2 dogs, spikes and sharp waves in 2 dogs, focal attenuation in 2 cases) and generalized abnormal activities in 4 dogs (generalized slow waves in 4 dogs and generalised spikes and sharp waves in 1 dog). The percentage of EEG interictal epileptiform discharges (66.67% of dogs had spikes, sharp waves, spikes and sharp waves complexes) was greater than seizures clinical seen (33.33% of dogs). In conclusion , EEG gived us important information about the severity of changes induced by hydrocephalus. Furthermore, this test is useful in the diagnosis of seizures associated with hydrocephalus and allows monitoring the therapeutic effects of antiepileptic drugs.

A MUTATION IN THE DNMT1 GENE CAUSING AUTOSOMAL DOMINANT ATAXIA WITH DEAFNESS AND CATAPLEXY

We describe the clinical features of the first UK family with the recently described autosomal dominant cerebellar ataxia, deafness and narcolepsy associated with mutations in exon 21 of the DNMT1...

Feasibility of focal transcranial DC polarization with simultaneous EEG recording: Preliminary assessment in healthy subjects and human epilepsy

We aimed to investigate the feasibility of an experimental system for simultaneous transcranial DC stimulation (tDCS) and EEG recording in human epilepsy. We report tolerability of this system in a cross-over controlled trial with 15 healthy subjects and preliminary effects of its use, testing repeated tDCS sessions, in two patients with drug-refractory Continuous Spike-Wave Discharges During Slow Sleep (CSWS). Our system combining continuous recording of the EEG with tDCS allows detailed evaluation of the interictal activity during the entire process. Stimulation with 1mA was well‐tolerated in both healthy volunteers and patients with refractory epilepsy. The large reduction in interictal epileptiform EEG discharges in the two subjects with epilepsy supports further investigation of tDCS using this combined method of stimulation and monitoring in epilepsy. Continuous monitoring of epileptic activity throughout tDCS improves safety and allows detailed evaluation of epileptic activity changes induced by tDCS in patients.

Levetiracetam reduces the frequency of interictal epileptiform discharges during NREM sleep in children with ADHD

Background Symptoms of attention deficit hyperactivity disorder (ADHD) are more common in children with epilepsy than in the general paediatric population. Epileptiform discharges in EEG may be seen in children with ADHD also in those without seizure disorders. Sleep enhances these discharges which may be suppressed by levetiracetam. Aim To assess the effect of levetiracetam on focal epileptiform discharges during sleep in children with ADHD. Method In this retrospective study a new semi-automatic quantitative method based on the calculation of spike index in 24-h ambulatory EEG recordings was applied. Thirty-five ADHD children, 17 with focal epilepsy, one with generalised epilepsy, and 17 with no seizure disorder were evaluated. Follow-up 24-h EEG recordings were performed after a median time of four months. Results Mean spike index was 50 prior to levetiracetam treatment and 21 during treatment. Seventeen children had no focal interictal epileptiform discharges in EEG at follow-up. Five children had a more than 50% reduction in spike index. Thus, a more than 50% reduction in spike index was found in 22/35 children (63%). Out of these an improved behaviour was noticed in 13 children (59%). Conclusion This study shows that treatment with levetiracetam reduces interictal epileptiform discharges in children with ADHD. There is a complex relationship between epilepsy, ADHD and epileptiform activity, why it is a need for prospective studies in larger sample sizes, also to ascertain clinical benefits.

Effect of medication withdrawal on the interictal epileptiform EEG discharges in presurgical evaluation

Medication withdrawal (MW) is an important method of provoking seizures and activating epileptiform EEG activity during the diagnostic work-up of patients evaluated for epilepsy surgery. Previously it was suggested that MW might influence the seizure-type and activate cortical areas otherwise not producing epileptiform discharges, leading to a false localization of the irritative zone. In order to investigate this we reviewed 42 consecutive cases of MW, of 36 patients, during a 3-year period. We compared seizure frequency, seizure-types and the localization of interictal epileptiform discharges before and after MW. Seizure frequency was significantly higher after MW. In the whole group we found an increase in seizure propagation: the proportion of the complex partial seizures and secondarily generalised seizures increased, while the proportion of the simple partial seizures decreased following MW. In one-third of the patients the interictal EEGs after the MW were different from those recorded before the MW. However, in these discordant cases the EEG findings after the MW (and not before the MW) were concordant with the seizure onset zone and the lesional zone. We conclude that MW is an effective and reliable seizure provoking method, and it does not lead to false localization of the irritative zone.

1H‐MR Spectroscopy Indicates Severity Markers in Temporal Lobe Epilepsy: Correlations between Metabolic Alterations, Seizures, and Epileptic Discharges in EEG

In this study, hippocampal metabolite alterations in (1)H-MR spectroscopy ((1)H-MRS) were correlated to the findings of intensive video-EEG monitoring and duration of seizure symptoms in patients with temporal lobe epilepsy (TLE). The 14 patients with mesial TLE and no pathological findings in imaging were investigated by (1)H-MRS. Seizures were analyzed by: number of clinical seizures in 24 h, exact duration of clinical symptoms in 24 h, frequency of interictal epileptiform discharges (IEDs) and ictal activity, duration of ictal activity, and IEDs occurring within 24 h in intensive EEG monitoring. Pearson Correlation Coefficient (PCC) was calculated between spectral metabolite alterations and the parameters mentioned above. In the analysis, a negative correlation was found between total (t) NAA values and degree of IEDs in EEG (p = 0.04); a positive correlation was found between Cr levels and duration of seizure symptoms registered by video monitoring (p = 0.01). Our study shows that, in some patients, (1)H-MRS is able to refer the severity of TLE. The degree of tNAA reduction in (1)H-MRS, probably indicating neuronal dysfunction, is associated with interictal spiking in intensive EEG monitoring. Duration of seizure symptoms associated with increased Cr peaks probably reflects increased gliosis.

FMRI temporal clustering analysis in patients with frequent interictal epileptiform discharges: Comparison with EEG-driven analysis

Temporal clustering analysis (TCA) is an exploratory data-driven technique that has been proposed for the analysis of resting fMRI to localise epileptiform activity without need for simultaneous EEG. Conventionally, fMRI of epileptic activity has been limited to those patients with subtle clinical events or frequent interictal epileptiform EEG discharges, requiring simultaneous EEG recording, from which a linear model is derived to make valid statistical inferences from the fMRI data. We sought to evaluate TCA by comparing the results with those of EEG correlated fMRI in eight selected cases. Cases were selected with clear epileptogenic localisation or lateralisation on the basis of concordant EEG and structural MRI findings, in addition to concordant activations seen on EEG-derived fMRI analyses. In three, areas of activation were seen with TCA but none corresponding to the electro-clinical localisation or activations obtained with EEG driven analysis. Temporal clusters were closely coincident with times of maximal head motion. We feel this is a serious confound to this approach and recommend that interpretation of TCA that does not address motion and physiological noise be treated with caution. New techniques to localise epileptogenic activity with fMRI alone require validation with an appropriate independent measure. In the investigation of interictal epileptiform activity, this is best done with simultaneous EEG recording.

Which seizure-precipitating factors do patients with epilepsy most frequently report?

When treating patients with epilepsy, dealing with seizure-precipitating factors is a partly neglected and underestimated supplement to more traditional therapies. The aim of this study was to investigate the incidence of seizure precipitants in a large epilepsy population and to determine which precipitants patients most often reported. Study participants included twins and their family members ascertained from the Norwegian Twin Panel (NTP), the Danish Twin Registry (DTR), and the Mid-Atlantic Twin Registry (MATR). One thousand six hundred seventy-seven patients with epilepsy were identified and were asked about seizure precipitants using a closed-ended questionnaire. Fifty-three percent reported at least one seizure-precipitating factor, while 30% claimed to have experienced two or more such factors. Emotional stress, sleep deprivation, and tiredness were the three most frequently reported precipitants. Patients with generalized seizures seemed to be more sensitive to sleep deprivation and flickering light than those with partial seizures, while women with partial seizures appeared to be more prone to seizures during menstruation than women with generalized seizures. Knowledge of seizure precipitants has practical implications, not only in patient treatment and counseling, but also for diagnosis, in that it may be helpful in facilitating the appearance of interictal epileptiform discharges in EEG and ictal EEG recordings.

Effects of epileptiform EEG discharges on cognitive function: Is the concept of “transient cognitive impairment” still valid?

In this article we review the existing evidence on the cognitive impact of interictal epileptiform EEG discharges. Such cognitive impairment occurs exclusively in direct relation to episodes of epileptiform EEG discharges and must be distinguished from (post) ictal seizure effects and from the nonperiodic long-term “stable” interictal effects caused by the clinical syndrome or the underlying etiology. Especially in patients with short nonconvulsive seizures, characterized often by difficult-to-detect symptoms, the ictal or postictal effects may be overlooked and the resulting cognitive effects may be erroneously related to the epileptiform EEG discharges. The existing epidemiological data show that the prevalence of cognitive impairment during epileptiform EEG discharges is low. In one study 2.2% of the patients referred to a specialized epilepsy center for EEG recording showed a definite relationship between epileptiform EEG discharges and cognitive impairments (“transient cognitive impairment”). Several studies have sought to analyze to what extent cognitive impairment can be attributed to epileptiform EEG discharges among the other epilepsy factors (such as the effect of the clinical syndrome). These studies show that epileptiform EEG discharges have an additional and independent effect, but this effect is mild and limited to transient mechanistic cognitive processes (alertness, mental speed). This finding concurs with clinical studies that also reported only mild effects. In only exceptional cases are epileptiform EEG discharges the dominant factor explaining cognitive impairment. In addition, some studies have indicated that such mild effects may accumulate over time (when frequent epileptiform EEG discharges persist over years) and consequently result in effects on stable aspects of cognitive function such as educational achievement and intelligence. Hence, the clinical relevance is that early detection of cognitive effects of epileptiform EEG discharges and subsequent treatment may prevent a definite impact on cognitive and educational development. The disruptive effects of epileptiform EEG discharges on long-term potentiation, as established in animal experiments, may be one of the neurophysiological mechanisms underlying this accumulation. In conclusion the concept of “transient cognitive impairment” is still valid, but refinement of methodology has shown that a large proportion of presumed transient cognitive impairment can be attributed to subtle seizures, while interictal epileptic activity accounts for a much smaller part of the cognitive effects than previously thought. In particular cryptogenic partial epilepsies are associated with the risk of cognitive impairment. We hope that increased clinical awareness of this need for early detection will stimulate longitudinal and prospective research that eventually also will provide an answer to the questions of when and how epileptiform discharges that are not part of a seizure need to be treated.

EEG quality during simultaneous functional MRI of interictal epileptiform discharges.

This article concerns the evaluation of the quality of interictal epileptiform EEG discharges recorded throughout simultaneous echo planar imaging (EPI). BOLD (blood oxygen level dependent) functional MRI (fMRI) images were acquired continuously on a patient with intractable epilepsy. EEG was sampled simultaneously, during and after imaging, with removal of pulse and imaging artifacts by subtraction of channel-specific running averages. Contiguous EEG epochs recorded with and without fMRI (fMRI+ve vs. fMRI-ve) were next randomized and presented to two blinded observers. Epileptiform discharges were identified retrospectively, and comparison was made in terms of the number of identified events, their amplitude, and spatiotemporal distribution. A spectral analysis was also performed on the EEG. In the randomized comparison of EEG segments, 80 (fMRI+ve) vs. 69 (fMRI-ve) discharges were noted with good interobserver agreement (69%). There were no significant differences in amplitude or spatio-temporal distribution. Comparison of the events detected and measured by two expert observers demonstrated that the Interictal Epileptiform Discharge (IED) characteristics were indistinguishable with and without scanning. We review briefly the existing literature on EEG recording quality for combined EEG/fMRI.

Respiratory disorders during sleep in patients with epilepsy: effect of ventilatory therapy on EEG interictal epileptiform discharges

Objective: Sleep disorders are common and may coexist with a variety of diseases, including epilepsy, with important implications for the clinical management of the latter. Sleep fragmentation and deprivation, and hypoxia associated to sleep disordered breathing (SDB) may contribute to the occurrence of seizures. On the other hand, antiepileptic drugs may worsen SDB by reducing the muscle tone of the upper airways, and increasing the arousal threshold. There is evidence indicating that treatment of the SDB can reduce both frequency and intensity of seizures. This study aimed at further understanding the relationship between SDB and epilepsy, particularly the influence of SDB on epileptogenicity – as evaluated by a quantitative analysis of interictal epileptogenic activity. Methods: Eight consecutive patients affected by partial epilepsy associated to SDB (OSAS or an association between chronic obstructive pulmonary disease – COPD – and snoring) underwent two nocturnal polysomnographies (PSG) – before and after ventilatory therapy with CPAP (in 6 patients with OSAS) or oxygen (in two patients with COPD and snoring). Spiking was quantified during the first sleep cycle in both PSG studies, and spiking rates were calculated both for the entire sleep cycle and for each separate sleep phase (NREM 1, NREM 2, NREM 3–4, REM and wake time after sleep onset – WASO). Results: In all patients, the improvement of the SDB after ventilatory treatment – as demonstrated by a reduction of the respiratory disturbances index (RDI) – was associated to a reduction of spiking rates, both in the entire cycle and in relationship to slow wave sleep. This reduction was particularly marked in patients with higher spiking rates in baseline conditions. Conclusion: Our data show that SDB treatment reduces the interictal epileptogenic activity, suggesting that SDB plays a role in increasing epileptogenicity. Further studies will be necessary to clarify the mechanisms whereby this reduction in epileptogenicity occurs, although improved sleep stability seems to play an important role. The presence of an underlying SDB in patients with refractory epilepsy should be investigated.