Long-term video-EEG monitoring revisited. The value of interictal and ictal video-EEG recording, a follow-up study

[French guidelines on electroencephalogram]

Electroencephalography allows the functional analysis of electrical brain cortical activity and is the gold standard for analyzing electrophysiological processes involved in epilepsy but also in several other dysfunctions of the central nervous system. Morphological imaging yields complementary data, yet it cannot replace the essential functional analysis tool that is EEG. Furthermore, EEG has the great advantage of being non-invasive, easy to perform and allows control tests when follow-up is necessary, even at the patient's bedside. Faced with the advances in knowledge, techniques and indications, the Société de Neurophysiologie Clinique de Langue Française (SNCLF) and the Ligue Française Contre l'Épilepsie (LFCE) found it necessary to provide an update on EEG recommendations. This article will review the methodology applied to this work, refine the various topics detailed in the following chapters. It will go over the summary of recommendations for each of these chapters and underline proposals for writing an EEG report. Some questions could not be answered by the review of the literature; in those cases, an expert advice was given by the working and reading groups in addition to the guidelines.

Interobserver variability of seizure semiology between two neurologist and caregivers

PURPOSE

We aimed to compare the extent of inter-observer variability in the description of seizure semiology between both neurologists and caregivers.

METHOD

We prospectively investigated 93 consecutive patients monitored over the past 5 years in our video-EEG unit. The videotaped seizures of the patients were reviewed independently by two neurologists who were blind to the clinical data. The questionnaires were completed by neurologists and caregivers. Interobserver rate of agreement between neurologists and caregivers was analyzed by using the kappa analysis and intraclass correlation coefficients.

RESULTS

There was excellent agreement for questions regarding whether the patient's eyes remained open, laterality of head deviation, arm movements, and ictal period. On the other hand, interobserver rate of agreement was fair to moderate for the laterality of hand automatisms, the presence of nose-wiping, and oral clonic jerks.

CONCLUSION

Besides variability in interobserver agreement among clinicians, the variability or concordance between physicians and caregivers are also of great importance, especially in case of epilepsy, where the accurate description of the attacks is the major determinant of an accurate diagnosis.

Usefulness of Video-EEG monitoring in patients with drug-resistant epilepsy

OBJECTIVE

To evaluate the characteristics of patients on whom long-term Video-EEG monitoring is performed in a specialist centre and to assess its suitability to study refractory epilepsy patients.

METHODS

A prospective analysis and study of Video-EEG monitoring was performed in a series of 100 refractory epilepsy patients from a single centre. The analysis included demographic data, the time until the first seizure, the methods used to provoke seizures, and the outcome (usefulness, change in the management, pharmacological and surgical improvement). A subgroup analysis based on diagnosis was performed.

RESULTS

The study was performed mainly on young people (mean 34.4 years) and the first seizure appeared in a mean of 30hours, requiring most of the patients to withdraw the medication. Nevertheless, there were no cases of status epilepticus. The usefulness of the test was high in all the groups. The management was changed in 65% of the patients with pharmacological and surgical improvement.

CONCLUSION

Long-term Video-EEG monitoring is a suitable test to study refractory epilepsy patients. The main problem in our country is accesibility.

Video/EEG monitoring in the evaluation of paroxysmal behavioral events: duration, effectiveness, and limitations

To establish the number of monitoring days needed to distinguish psychogenic nonepileptic seizures (PNES) from epileptic seizures (ES) in adult patients admitted for video/EEG monitoring (VEM), we performed a retrospective chart review on 199 consecutive admissions for behavioral event diagnosis with VEM. Of the 199 adult patients admitted for VEM, 83.9% (n = 167) had a clinical event during admission, and a definitive diagnosis was made in 75.9% (n = 151). Of patients who had clinical events, 87.7% (n = 143) had their first event on admission day 1 or 2. Factors associated with ES (vs PNES) included an abnormal baseline EEG (P < 0.001), an abnormal brain MRI (P = 0.01), and history of events lasting less than 1minute (P = 0.01). There was no association between time to first event and discharge diagnosis. VEM differentiated between ES and PNES in the majority of adult patients evaluated. Most behavioral events were characterized within 2 days of admission.

Video-EEG telemetry can be a crucial tool for neurologists experienced in epilepsy when diagnosing seizure disorders

We retrospectively reviewed the charts of 121 patients consecutively admitted to our epilepsy-monitoring unit (VET) during the period of 01 July 2001 to 31 December 2002. We excluded patients with a confirmed diagnosis of epilepsy who were admitted for invasive pre-surgical monitoring. Medical records were reviewed to collect demographic and clinical information that lead to the initial referral for VET by neurologists with expertise in epilepsy or by an epileptologist. We identified 29 patients (24%), whose diagnosis changed after VET. Their seizure duration ranged from 1 to 46 years. A diagnosis of epileptic seizures (ES) was made in four of the patients who were initially felt to have nonepileptic seizures (NES). The diagnosis of NES was made in 22 patients who were initially felt to have ES. All of these 29 patients had failed at least two or more antiepileptic drugs (AEDs). A misclassification of epilepsy syndrome was found in three patients. Eleven of the NES patients had risk factors that would increase the likelihood of ES, including significant head injury (n=6), febrile seizures (n=2), meningioencephalitis (n=2), and tumours (n=1). Four of these 11 patients had abnormal interictal EEGs. We conclude that VET is crucial in establishing a diagnosis in patients with seizures. Without VET, patients can be misclassified or receive ineffective treatment, even when being treated by specialists in epilepsy. Thus, VET, can help facilitate the most appropriate type of therapy in difficult to control patients.

A review of diagnostic techniques in the differential diagnosis of epileptic and nonepileptic seizures

The diagnosis of psychogenic nonepileptic seizures (PNES) is complex. Long-term electroencephalogram monitoring with video recording (video EEG) is the most common method of differential diagnosis of epilepsy and PNES. However, video EEG is complex, costly, and unavailable in some areas. Thus, alternative diagnostic techniques have been studied in the search for a diagnostic method that is as accurate as video EEG, but more cost effective, convenient, and readily available. This paper reviews the literature regarding possible diagnostic alternatives and organizes findings into 7 areas of study: demographic and medical history variables, seizure semiology, provocative testing, prolactin levels, single photon emission computed tomography, psychological testing, and neuropsychological testing. For each area, the literature is summarized, and conclusions about the accuracy of the technique as a diagnostic tool are drawn. Overall, it appears unlikely that any of the reviewed alternative techniques will replace video EEG monitoring; rather they may be more successful as complementary diagnostic tools. An important focus for further investigations involves combinations of diagnostic techniques for the differential diagnosis of epilepsy and PNES.

An audit of ambulatory cassette EEG monitoring in children

This audit evaluated the role and usefulness of ambulatory cassette EEG recordings without simultaneous video monitoring in children with paroxysmal episodes including epilepsy. Fifty-four children underwent ambulatory EEG recordings for 48 hours over a 12 month period. Only 31 of the 54 children experienced one of their typical clinical episodes during their recordings. Fifteen of these 31 patients were considered to have epilepsy, only three of whom had a clinical episode at the time of their recording and in all three the EEG demonstrated abnormal (generalized spike and slow wave or focal, rhythmic slow wave) activity. All 10 patients who were considered to have non-epileptic episodes showed no electrical change during their EEG recordings. The results of the ambulatory cassette EEG recordings were considered to have been helpful and to have contributed to the management of only 17 (31%) of the 54 patients in this audit. Stricter clinical criteria for undertaking ambulatory recordings and improved technology are likely to increase the role and usefulness of this procedure.

The absence of interictal spikes with documented seizures suggests extratemporal epilepsy

PURPOSE

To determine the demographic and clinical characteristics of patients who have documented epileptic seizures on long-term video-EEG monitoring who do not have interictal spikes.

METHODS

The records of 1,223 monitoring studies from 919 patients who underwent noninvasive long-term video-EEG monitoring were reviewed. In 28 patients (3.0% of monitored patients, 4.4% of patients with electrographic evidence of epilepsy), no interictal spikes were found despite the occurrence of at least one recorded electrographic seizure. The demographic, medical, neuropsychological, and EEG data of these patients were compared with those of 28 matched control patients with documented interictal spikes.

RESULTS

Extratemporal seizures were significantly more frequent in the patients with at least one recorded epileptic seizure but without interictal spikes compared with patients with epileptic seizures and interictal spikes (p = 0.031). The only other significant difference between the groups (p = 0.016) was a later age at seizure onset (18.3 vs. 10.7 years) for the patients without interictal spikes. Age at evaluation, gender, handedness, clinical seizure type, family history of epilepsy, history of febrile seizures, neuropsychological testing, and neurologic and psychiatric history did not differ between the two groups.

CONCLUSIONS

In patients with documented epilepsy without interictal spikes on EEG monitoring, the possibility of an extratemporal focus should be considered.

Lamotrigine analysis in blood and brain by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatography assay was developed and validated to determine plasma and brain lamotrigine concentrations allowing pharmacokinetic-pharmacodynamic studies of this new antiepileptic drug in patients and laboratory animals. Lamotrigine and its internal standard were extracted, under alkaline conditions, from plasma and brain homogenate, into ethyl acetate; brain proteins were previously precipitated with trichloroacetic acid. The method was linear between 0.1 and 15.0 mg/l for plasma, with a detection limit of 0.008 mg/l, and between 0.1 and 5.0 mg/l for brain homogenate, with a detection limit of 0.023 mg/l. The method proved to be simple, useful and appropriate, not only for clinical and experimental research, but also for routine monitoring of lamotrigine concentrations in patients.

Surgical treatment of epilepsy

Approximately 30-40% of patients with focal epilepsy continue to have seizures despite appropriate medical therapy. Surgical treatments should be considered in this important subset of patients. Recent advances in neuroimaging technology have revolutionized the identification and evaluation of surgical candidates. The goal of the presurgical evaluation (video EEG monitoring, neuroimaging, and neuropsychological assessment) is to delineate the epileptogenic zone. Surgery is recommended when this has been adequately identified and the proposed procedure is expected to result in a high likelihood of seizure freedom and a low risk of neurologic and cognitive morbidity.

Temporal lobe epilepsy surgery: definition of candidacy

Medical intractability is one of the absolute indications for considering temporal lobe epilepsy surgery. This is a relative concept that has to be highly individualized. It is quite easy to determine when a patient's seizures are fully controlled. On the other hand, "continuing seizures are not necessarily a measure of intractability or disability". A positive decision to operate would be based on some of the following factors: assurance of a firm diagnosis, seizures that are frequent and disabling, and seizures occurring in patients who are drug refractory to optimal anti-epileptic medications and dosages.

The role of patient companions in long-term video-EEG monitoring

In developing countries it is difficult to have full-time dedicated nurses in Epilepsy Monitoring Units (EMU). Our one-bed EMU is within the Neurology Service and is adequately staffed during daytime working hours only. So we created a new model where the patient's companion was asked to press a nurse call button, allowing the examination of the patient by the nurse. In this study we aimed to understand how patient companions behaved and which factors influenced their behaviour. Patients were allowed to choose a single companion who were educated by the specialist monitoring nurse according to a protocol. Only the first recorded seizures of the patients were included in the study. The seizures were reviewed from the video-cassette recordings and the behaviour of the companions was scored according to the results of the following three questions: (1) when was the seizure noticed?; (2) was the nurse call button pushed?; and (3) did the companion prevent the recording of the seizure by the camera? The companions were grouped according to the following criteria; age, sex, level of education, type of relationship. The scores were compared for each criterion separately. The behaviours of the 50 companions (34F, 16M; age: 25-72) were studied. When statistically compared for age, sex and level of education, there were no significant differences between different groups. However, the mean score of the 47 companions who were immediate family members (3.72) was greater than those three who were not (1.66) In one-bed EMUs, patient companions who are family members can help nurses in the early detection of seizures.

The role of quantitative ictal SPECT analysis in the evaluation of nonepileptic seizures

Nonepileptic seizures may represent difficult diagnostic problems. Identifying their presence and frequency is critical for determining appropriate treatment. The authors investigated the value of quantitative perfusion changes as measured by ictal single-photon emission tomography (SPECT) difference images in differentiating nonepileptic from epileptic seizures. Eleven patients with a clinical suspicion of nonepileptic events had ictal and interictal technetium-99m hexamethylpropylene amine SPECT scans during continuous audiovisual surface electroencephalogram (EEG) monitoring. The authors analyzed perfusion difference images based on registration, normalization, and subtraction of ictal and interictal SPECT images. The difference images were registered to each patient's magnetic resonance imaging scan to anatomically localize ictal perfusion changes. Three of 11 patients also carried the diagnosis of epilepsy and were taking antiepileptic medication. Five patients were taking antiepileptic drugs, but the diagnosis of epilepsy was not confirmed. In all patients, continuous video EEG monitoring revealed no ictal EEG findings. In nine of these patients, visual interpretation of ictal SPECT was suggestive of localized increased (n = 6) or decreased perfusion (n = 3). In all patients, however, no blood flow changes were noted on quantitative SPECT analysis with injections performed during the seizure-like event, suggesting the diagnosis of pseudoseizures. The authors' results suggest that quantitative ictal SPECT analysis is a useful tool in the diagnosis of nonepileptic seizures.

Long-term inpatient audiovisual scalp EEG monitoring

Long-term audiovisual scalp EEG monitoring is an essential diagnostic tool for the evaluation of paroxysmal disorders. The definitive classification of both nonepileptic and epileptic events is often possible only with the use of this technique. Assessment of response to treatment and the noninvasive presurgical localization of seizure foci are other important uses. The optimization of both clinical semiology and electrophysiologic data obtained from such studies is the subject of significant research efforts. Outcomes studies and advanced EEG analysis research should ultimately serve to minimize the cost of this valuable technique as well as maximizing its utility.

Epilepsy: a costly misdiagnosis

Nonepileptic events misdiagnosed as manifestations of epilepsy are a significant problem. Five representative cases suggest that a diagnosis of epilepsy should be based on a careful history and analysis of the clinical event. The clinician should make a diagnosis of epilepsy only when there is definite positive support and not on the basis of poorly characterized paroxysmal episodes and a few minor and nonspecific EEG findings. Effective treatment presupposes correct diagnosis and early diagnosis appears to be correlated with better prognosis. The annual cost of nonepileptic spells misdiagnosed as epileptic can be estimated at between $650,000,000 and $4,000,000,000. Aggressive efforts to establish a definite diagnosis of spells not clearly epileptic is both medically and economically indicated.

Dipole modeling in epilepsy surgery candidates

PURPOSE

The validity and clinical significance of dipole modeling in epilepsy surgery candidates is not fully established.

PATIENTS AND METHODS

Interictal and ictal dipole modeling was performed in 43 patients with refractory complex partial seizures (CPS) and intracranial structural abnormalities demonstrated with optimum magnetic resonance imaging (MRI: space-occupying, n = 15; atrophic, n = 26; dysplastic, n = 2). Video-EEG monitoring showed CPS in all patients. In 12 patients, additional intracranial EEG monitoring demonstrated hippocampal seizure onset in 11 patients and medial occipital ictal onset in 1.

RESULTS

Spatiotemporal dipole mapping of averaged interictal spikes and epochs of early ictal discharges revealed two distinct dipole patterns. Patients with lesions located in the medial (+/-lateral) temporal lobe (n = 34) and medial occipital lobe (n = 1) uniformly presented a combined interictal dipole that consisted of a radial and a tangential component with a high degree of elevation relative to the axial plane. Eight of 9 patients with extratemporal lesions had a less stable dipole with a predominant radial component. Ictal dipole modeling identified the ictal onset zone correctly as compared with intracranial EEG recordings from bilateral hippocampal depth electrodes. Ictal dipoles showed a striking correspondence with the interictal dipoles in individual patients.

CONCLUSIONS

Interictal and ictal dipole mapping provided additional, reliable, and relevant localizing information in surgical candidates for refractory CPS. Ictal dipole analysis may limit the number of patients who require intracranial electrodes.

Dipole modelling and intracranial EEG recording: correlation between dipole and ictal onset zone

This study includes 11 patients (3 males, 8 females) with mean age of 29 years (range: 15-42 years) who underwent a presurgical evaluation for refractory complex partial seizures (CPS). In all patients, neuroimaging (1.5 T optimum-MR) demonstrated intracranial structural abnormalities (space-occupying: n = 2; atrophic: n = 8; dysplastic: n = 1) and video-EEG monitoring showed CPS, because of discrepancies in the non-invasive examinations, all underwent additional intracranial EEG monitoring. After tailored resective procedures, all but one patient became seizure free. Mean follow-up was 30 months (range: 12-52 months). Results of intracranial EEG recording were compared with spatiotemporal dipole mapping of interictal and ictal epileptic discharges. Interictal dipole modelling revealed two distinct dipole patterns. Patients with lesions located in the medial temporal lobe uniformly presented a combined dipole that consisted of a radial and a tangential component with a high degree of elevation relative to the axial plane. Patients with extrahippocampal lesions had a less stable dipole with a predominant radial component. Dipole modelling of early ictal discharges revealed a striking correspondence with the interictal findings in individual patients. Elevation of ictal dipoles was always congruent with localisation based on intracranial EEG recordings. Interictal and ictal dipole mapping of medial temporal lobe sources may limit the number of surgical candidates for refractory CPS that need intracranial EEG recording. Whether ictal dipole modelling can be equally useful in extratemporal epilepsy remains to be proven.

Interictal and ictal dipole modelling in patients with refractory partial epilepsy

Fifteen patients (7 men, 8 women) with mean age of 34 years and mean duration of refractory partial seizures of 17 years were included in a presurgical evaluation protocol. Neuroimaging (CAT, 1.5 T MR) demonstrated intracranial structural lesions (space-occupying: n = 9; atrophic: n = 6) and video-EEG monitoring showed complex partial seizures in all patients. Four patients underwent additional intracranial EEG monitoring that demonstrated hippocampal seizure onset in all. Voltage topography and spatiotemporal dipole mapping of interictal epileptic discharges revealed two distinct distinct dipole types. Patients with lesions in the medial (and lateral) temporal lobe uniformly presented with a negative voltage field with a steep gradient over the inferior temporal area and a stable, combined dipole that consisted of a radial and a tangential component with a high degree of elevation relative to the axial plane. Patients with extratemporal lesions had a more diffuse, less dipolar voltage field and a corresponding dipole which was less stable and had a predominant radial component. Dipole modelling of epochs of early ictal discharges revealed a striking correspondence with the interictal findings in individual patients. Interictal spike voltage topography and corresponding dipole mapping provided additional and reliable information that was relevant in surgical candidates for refractory partial epilepsy, e.g. by suggesting in some patients that the medial temporal structures were not primarily involved. Ictal dipole modelling revealed concordant results with interictal data. It shows promising but needs further confirmation and validation in a larger patient population with intracranial EEG recordings. Despite intrinsic limitations, spike voltage topography and dipole mapping contributes to a better localisation of the underlying brain source of epileptic discharges.

Clinical and neurophysiological correlations in patients with refractory partial epilepsy and intracranial structural lesions

Twenty patients (13 males, 7 females), who presented with refractory partial epilepsy and a CT and/or MR detected intracranial intra-axial structural lesion were admitted to the University of Gent Epilepsy Monitoring Unit. Mean duration of the epilepsy was 17 years (2-47 years). All patients were enrolled in a comprehensive presurgical protocol including neurological examination, video-scalp-EEG monitoring with prolonged interictal and ictal recording, neuropsychological assessment and positron emission tomography (PET). Intracranial EEG monitoring was performed in 5 patients in whom discrepancies between different tests were found during the non-invasive evaluation. Clinical neurological examination was normal in 16 patients; 4 patients had a mild contralateral hemiparesis. Lesions were mainly located in the temporal lobe (55%). Most patients presented with complex partial seizures (90%). Clinical seizure characteristics correlated well with the lesion location in 55% of patients. Interictal EEG showed focal epileptic activity and focal slowing in respectively 85% and 30% of patients. Interictal EEG lateralization was congruent with the side of the lesion in 17 patients (85%). Interictal EEG localization was congruent with the lobe of the lesion in 13 patients (65%). Ictal EEG lateralized correctly in 14 patients (70%) and localized correctly in 10 patients (50%). Neuropsychological assessment lateralized and localized congruently in respectively 8/17 (47%) and 7/17 (41%) of patients. Interictal PET showed focal interictal hypometabolism, congruent with the lesion, in 13/16 (81%) of patients. Intracranial EEG was congruent with the lesion location in 3 patients but non-congruent in 2 patients. All patients underwent surgical procedures: average follow-up was 14 months (6-24 months). Complete surgical removal of the lesion with free margins resulted in a more than 90% reduction of seizures without postoperative neurological deficit in 12/13 patients.