Interictal indices of temporal seizure origin

Two studies assessed the value of temporal lobe interictal electroencephalographic (EEG) spikes and delta in indicating side of temporal epileptogenesis. The first study determined laterality of spikes/delta in awake recordings of 56 patients whose seizures all began unilaterally as proven by (1) EEG-recorded seizures and (2) >90% improvement after lobectomy. Spikes of 52 (93%) and delta of 46 (82%) patients predominated or appeared exclusively ipsilateral to seizure origin. Neither predominated contralaterally in any patient. The second study investigated laterality of temporal seizures in a separate group of 156 patients with various side vs side spike or delta ratios on 1 to ≥4 awake recordings. Ninety-nine of 104 patients (95%) with temporal spikes on four or more awake recordings had most or all seizures ipsilateral to most spikes, including 79 of 80 (99%) of those with ≥3 side vs side spike ratios. Among the 120 patients with high (≥3) side vs side spike ratios, most or all seizures of 118 (98%) originated ipsilateral to most spikes. Predominant seizure origin also correlated with lateralized arrhythmic delta—from 90% ipsilateral seizures of those with one EEG with delta to 100% with ≥4 such EEGs. Data from these two studies using opposite directions of analysis (seizures ← spikes/delta and spikes/delta → seizures) demonstrate high correlations between laterality of interictal and ictal entities, particularly if temporal spikes clearly predominate on one side and if unilateral temporal delta activity persists over several recordings. Such correlations suggest that the awake interictal scalp EEG cannot be ignored when assessing laterality of temporal epileptogenesis.     

Effective Temporal Lobectomy in Childhood Without Invasive EEG

Summary: Temporal lobectomy abolished complex partial seizures (CPSs) in 14 consecutive children (12 years or younger) whose presurgical evaluation included clinical analysis, scalp EEG, and neuroimaging. Seizures of 13 of 14 patients began with a simple partial component whose symptoms were suggestive of limbic system involvement. EEG recorded clinically typical seizures arising from the ultimately operated on temporal lobe in seven (50%) and never falsely lateralized seizure origin. Most active interictal spikes arose from the epileptogenic temporal lobe in 13 (93%) and never falsely lateralized epileptogenesis. Neuroimaging disclosed epileptogenic lesions in all: magnetic resonance imaging (MRI; 11 patients) and computed tomography (CT; three patients). Children may obtain relief from CPSs by temporal lobectomy without invasive electroencephalography.     

Usefulness of Unilateral Interictal Sharp Waves of Temporal Lobe Origin in Prolonged Video-EEG Monitoring Studies

The value of EEG interictal epileptiform activity in predicting location of the seizure focus remains controversial. In 64 patients, scalp video-EEG monitoring studies showed one or two ipsilateral interictal foci in the temporal lobe. The site of these interictal foci correlated with location of the seizure focus recorded during prolonged video-electrocorticography (ECoG) with use of subdural grids placed under the mesiobasal temporal region and over the lateral temporal convexity. Our findings suggest that unilateral anterotemporal interictal foci can accurately predict location of seizure onset. This is also true in patients with two ipsilateral temporal interictal foci, provided that the dominant focus is localized in anterotemporal regions. We believe that in such patients invasive recordings are not warranted, but we caution against sole use of interictal epileptiform criteria for localization of the seizure focus. Correlation with clinical information, ictal EEG, neuropsychometric, and neu-roimaging studies is required before performance of epilepsy surgery.     

Current trends in electroencephalography

Several recent articles re-emphasize the value of clinical electrophysiology: in localizing epileptogenesis, predicting effectiveness of epilepsy surgery, and disclosing a mechanism of benign Rolandic epilepsy of childhood.A review of the role of EEG in the diagnosis of epilepsy indicated that epileptiform activity will appear in 50% of initial awake recordings of adults with epilepsy and in 85% of subjects undergoing two recordings. This contrasts with the appearance of spikes in only 4 of 1000 normal persons. Several studies focused on the value of electroencephalography in extratemporal epilepsy: 62% of patients with neocortical epilepsy had at least one localizing ictal EEG; occipital and temporal neocortical seizures were localized in a greater proportion than frontal or parietal attacks. Interictal spikes, if unifocal, always arose from the epileptogenic region in a study of their seizure localizing value. Such congruence augured for better seizure control by focal resection in two studies reviewed herein.Studies indicating the value of interictal temporal lobe spikes and scalp-recorded seizures in lateralising a temporal seizure focus are reviewed. One study found EEG to be slightly more reliable for lateralization of temporal epileptogenesis than MRI.In patients with benign Rolandic seizures, enhanced motor evoked potentials (MEPs) were obtained from transcranial magnetic stimulation when this was applied 50-80 msec after electrical stimulation of the thumb whereas this interval inhibited the MEP in normal subjects. This suggests that afferent cutaneous input abnormally and synchronously activates a large population of sensory neurons; such activation is subsequently transmitted to the motor cortex to produce the focal spikes in this condition.Finally, advances in non-invasive technology have redefined and limited the need for invasive monitoring in children with intractable seizure disorders.     

Interictal, unifocal spikes in refractory extratemporal epilepsy predict ictal origin and postsurgical outcome.

OBJECTIVES: To evaluate the significance of exclusively unifocal, unilateral, interictal epileptiform patterns on scalp electroencephalography (EEG) in surgical candidates with medically intractable extratemporal epilepsy. METHODS: We reviewed 126 patients with refractory extratemporal partial seizures who underwent epilepsy surgery at our center. All were followed for at least 2 years after resections. Surgery was based on ictal EEG recordings. We examined ictal onsets and surgical outcome in subjects whose preoperative, interictal scalp EEGs during long-term monitoring (LTM) demonstrated only unilateral, well-defined focal discharges, and outcome in patients whose interictal EEGs during LTM showed bilateral, non-localized, or multifocal epileptiform patterns. RESULTS: We found that 26 subjects exhibited only unilateral, unifocal, interictal epileptiform patterns. In all 26 cases (100%) clinical seizures arose from the regions expected by the interictal findings (P<0.0001, Sign test). At last follow-up 77% (20/26) of these patients were seizure-free, while 23% (6/26) had >75% reduction in seizures. This compares to the remaining patients, of whom 34% (34/100) were seizure-free, 41% (41/100) had >75% reduction in seizures, and 25% (25/100) had <75% reduction in seizures (P=0.0001, Fisher's Exact test). CONCLUSIONS: Strictly unifocal, interictal epileptiform patterns on scalp EEG, though seen in a minority of subjects, may be an important, independent factor in evaluating subjects with intractable extratemporal, localization-related epilepsy for surgical therapy. This finding is highly predictive of both ictal onsets and successful postsurgical outcome.     

Electroencephalographic studies of simple partial seizures with subdural electrode recordings

We used subdural electrodes to study the EEG features of simple partial seizures in 7 patients. We detected epileptiform discharges in 61 of 68 subdurally recorded simple partial seizures compared with 6 of 55 simple partial seizures recorded with scalp electrodes (p less than 0.0001). The onset of 36 nonmotor simple partial seizures was detected only by the medial and basal temporal subdural electrodes, and the onset of 25 simple partial seizures with motor manifestations was recorded by subdural electrodes only from the lateral cortex of the posterior frontal lobe. There was a close correspondence between the area first involved in the epileptiform discharge during simple partial seizures and the area first involved during complex partial and secondary generalized tonic-clonic seizures. Subdural electrodes may be effective in localizing the onset and spread of simple partial seizures, including those that arise from the medial temporal lobe.     

Indices of resective surgery effectiveness for intractable nonlesional focal epilepsy

Among 70 patients with intractable focal epilepsy and no specific lesion, as determined by both MRI (magnetic resonance imaging) and histopathology, outcome after resective surgery was polarized: 26 (37%) became seizure free (SF), and 27 (39%) were not helped. Eighteen (42%) of 43 standard temporal resections rendered patients SF, somewhat more than eight (30%) of 27 other procedures. To seek reliable prognostic factors, the subsequent correlative data compared features of the 26 SF patients with those of the 27 not helped. Although ictal semiology guided the site of surgical resection, it and other aspects of seizure and neurologic history failed to predict surgical outcome. However, two aspects of preoperative scalp EEGs correlated with SF outcomes: (a) among 25 patients in whom >50% of clinical seizures arose from the later resected lobe and no other origins, 18 (72%) became SF compared with seven (28%) of 25 with other ictal profiles; (b) 13 (93%) of 14 temporal lobe patients whose interictal and ictal EEGs lacked features indicative of multifocal epileptogenesis became SF compared with five (33%) of 15 with such components. The considered need for subdural (SD) EEG reduced SF outcome from 18 (90%) of 20 patients without SD to eight (24%) of 33 with SD; this likely reflected an insufficient congruity of ictal semiology and interictal and ictal scalp EEG for localizing epileptogenesis. Within this SD group, >50% of clinical seizure origins from a later resected lobe increased SF outcome somewhat: from two (14%) of 14 without this attribute to six (40%) of 15 with it; 100% of such origins increased SF outcome from two (12%) of 16 to six (46%) of 13.     

Significance of Sharp Waves in Routine EEGs After Epilepsy Surgery

We retrospectively analyzed the presence of sharp waves in 2-h EEGs performed 6 months after epilepsy surgery in 59 patients. To study the significance of the postoperative interictal epileptiform activity in the tissue remaining after resection, we included only patients with a single epileptic focus (as defined preoperatively by prolonged video/EEG recordings and subdural electrode arrays studies) and no progressive structural lesions. Temporal lobectomy was performed in 51 patients (86%); extratemporal resections were performed in the remainder. The epileptogenic focus was completely resected in 26 patients (44%). The immediate postoperative electrocorticograms (EcoG) showed spikes in 13 patients (22%). At 6-month follow-up, 43 patients (73%) were seizure-free or had auras only and 12 patients (20%) had epileptiform activity on EEG. A significant correlation was noted between presence of sharp waves in the 6-month postoperative EEG and recurrence of seizures (Fisher's exact test p = 0.011) and also with the extent of the resection (complete vs. incomplete p = 0.042). We noted no correlation between postoperative epileptiform activity and location of the resection (temporal vs. extratemporal), presence of spikes in immediate postoperative EcoG, or occurrence of auras only at 6-month follow-up.     

Spatiotemporal relationship between seizure activity and interictal spikes in temporal lobe epilepsy.

PURPOSE: To analyze the spatio-temporal relationship between seizure propagation and interictal epileptiform discharges (IEDs) in patients with bitemporal epilepsy. METHODS: We investigated 18 adult patients with intractable temporal lobe epilepsy (TLE) who had undergone continuous video-EEG monitoring during presurgical evaluation. Only those patients were selected who had independent IEDs over both temporal lobes. Two authors evaluated the ictal and interictal EEG data independently. RESULTS: We analyzed 52 lateralized seizures of 18 patients. Thirty-one seizures showed ipsilateral seizure spread exclusively, whereas in 21 seizures the contralateral hemisphere was also involved. In lateralized seizures without contralateral propagation, we found that spikes ipsilateral to the seizure onset occurred postictally in a greater ratio than preictally (P<0.001). In lateralized seizures with contralateral propagation, we found no significant changes in the postictal spike distribution. CONCLUSIONS: Our findings showed that the lateralization of IEDs may depend on the brain areas involved by the preceding seizures, suggesting that spikes can be influenced by the seizure activity, and are not independent signs of epileptogenicity.     

Significance of Simple Partial Seizures in Temporal Lobe Epilepsy

Summary: We determined how localization of simple partial seizures (SPS) correlated with localization of complex partial seizure (CPS) in scalp/sphenoidal EEG and assessed prognosis after temporal lobe resective surgery in patients with an ictal correlate of SPS in scalp/sphenoidal EEG recordings. EEGs were recorded with the 10–20 system of electrode placement and supplemented with sphenoidal electrodes. Between 1985 and 1992, 183 patients with temporal lobe epilepsy (TLE) reported an aura (SPS) during inpatient monitoring; all were eligible for inclusion in our study. The EEGs during SPS showed ictal changes in 51 patients (28%, 117 SPS). Forty-four patients had unilateral temporal interictal spikes (IIS), and SPS and CPS always arose from the same region. Seven patients had bitemporal interictal spikes; SPS colocalized with CPS in 4 patients (57%), SPS were contralateral to CPS in 2 patients, and 1 patient had bilateral independent CPS but unilateral SPS. SPS accompanied by EEG ictal changes conveyed a favorable prognosis in patients who underwent epilepsy surgery. Scalp/sphenoidal recorded IIS but were less reliable in identifying the location of CPS onset in patients with bitemporal spikes.     

Use of cavernous sinus EEG in the detection of seizure onset and spread in mesial temporal lobe epilepsy

PURPOSE: The study goal was to evaluate the clinical usefulness of intravenous EEG recording by placing wire electrodes in the cavernous sinus (CS) and the superior petrosal sinus (SPS) in patients with intractable temporal lobe epilepsy (TLE), with special emphasis on the ictal recording. METHODS: We placed Seeker Lite-10 guide wire as electrodes in the bilateral CS, SPS, or both to simultaneously record both ictal and interictal EEGs with the scalp EEG in five patients with TLE. In addition, in one patient, we averaged interictal scalp and intravascular EEG time-locked to the epileptiform discharge recorded from the CS/SPS-EEG to further delineate the relationship of the spikes between scalp and intravenous recording. RESULTS: In four of five patients, clinically useful recording was obtained to determine ictal focus. We recorded habitual seizures in three patients, and the detailed characteristics of ictal epileptiform discharges were shown. The averaged waveform of interictal epileptiform discharges clarified the spike distribution in the scalp EEGs, which was otherwise undetectable in the single trace. All of the patients completed the intravenous EEG monitoring without any neurological or psychological problems. CONCLUSIONS: The CS/SPS-EEG is a relatively noninvasive method that is useful for the detection of ictal focus and its spreading pattern and thus for the selection of surgical candidate among patients with intractable TLE. Although the number of seizures detected during the short monitoring period may be limited, due to the advantages of its safety and simplicity, it is worth trying for potential surgical candidates before more invasive examinations are applied. A further study with a larger number of patients is needed to estimate its practical risk.     

Detection of temporal lobe spikes: Comparing nasopharyngeal, cheek and anterior temporal electrodes to simultaneous subdural recordings

OBJECTIVE: To compare nasopharyngeal (NP), cheek and anterior temporal (AT) electrodes for the detection yield and localization of interictal spikes in temporal lobe epilepsy. METHODS: In patients evaluated for epilepsy surgery with subdural electrocorticography electrodes, we simultaneously recorded NP, cheek and AT electrodes. Two observers identified spikes in EEG traces and marked in which channels they occurred. Interobserver agreement was calculated using Cohen's kappa. For localization, data-sets with high interobserver agreement (kappa-value 0.4) were evaluated. The subdural distribution of NP and AT spikes was mapped. RESULTS: Seven patients were included, six were analyzed for localization. Only 1.5% of spikes recorded by cheek electrodes were not seen on temporal leads, while 25% of NP spikes were not seen on either. Spikes only recorded by NP electrodes had mesiobasal, while AT spikes had lateral temporal distribution. CONCLUSIONS: NP electrodes can increase EEG spike detection rate in temporal lobe epilepsy and are more useful than cheek electrodes. Spikes that are seen only on NP electrodes tend to be mesiobasal temporal lobe spikes. SIGNIFICANCE: Adding NP electrodes to scalp EEG can aid interictal spike detection and source localization, especially in short recordings like MEG-EEG.     

Ictal Scalp EEG in Unilateral Mesial Temporal Lobe Epilepsy

Summary: Purpose: We wished to determine the predictive significance of unilateral hippocampal atrophy and interictal spikes on localization of ictal scalp EEG changes and assess whether ictal EEG provides information that might change treatment or influence prognosis in patients with such characteristics of epilepsy.
Methods: We analyzed EEG seizure patterns in 118 seizures in 24 patients with unilateral mesial temporal lobe epilepsy (MTLE) defined by typical clinical seizure semiology, unilateral hippocampal atrophy on magnetic resonance imaging (MRI) and unitemporal spikes on interictal EEG. Two blinded electroencephalographers independently determined morphology, location, and time course of ictal EEG changes.
Results: Lateralization was possible in 88.4–92.0% of seizures and always corresponded to the side of the interictal spike focus and of hippocampal atrophy on MRI. Although only 30.4–33.9% of seizures were lateralized at onset, a later significant pattern emerged (12.6–13.3 s after EEG seizure onset) that allowed lateralization in 82.4–91.O% of seizures with non-lateralized onset. Interobserver reliability for lateralization was excellent, with a K-value of 0.85. In most patients, either all (79.2–83.3%) or >50% (8.3–16.7%) of seizures were lateralized. In only a small proportion of patients (4.2–8.3%) were 40% of seizures lateralized. In 1 patient, no seizure could be lateralized by 1 electroencephalographer. The results of ictal EEG recordings did not alter the surgical approach and did not correlate with surgical outcome.
Conclusions: We conclude that unilateral hippocampal atrophy on MRI and unitemporal interictal spikes can predict localization of ictal scalp EEG changes with a high degree of reliability and that ictal EEG provides no additional localizing information in this particular patient group.     

Source localization of small sharp spikes: low resolution electromagnetic tomography (LORETA) reveals two distinct cortical sources.

OBJECTIVE: We have investigated the cortical sources and electroencephalographic (EEG) characteristics of small sharp spikes (SSS) by using statistical non-parametric mapping (SNPM) of low resolution electromagnetic tomography (LORETA). METHODS: We analyzed 7 SSS patterns (501 individual SSS) in 6 patients who underwent sleep EEG studies with 29 or 23 scalp electrodes. The scalp signals were averaged time-locked to the SSS peak activity and subjected to SNPM of LORETA values. RESULTS: All 7 SSS patterns (mean 72 individual SSS, range 11-200) revealed a very similar and highly characteristic transhemispheric oblique scalp voltage distribution comprising a first negative field maximum over ipsilateral lateral temporal areas, followed by a second negative field maximum over the contralateral subtemporal region approximately 30 ms later. SNPM-LORETA consistently localized the first component into the ipsilateral posterior insular region, and the second component into ipsilateral posterior mesial temporo-occipital structures. CONCLUSIONS: SSS comprise an amalgam of two sequential, distinct cortical components, showing a very uniform and peculiar EEG pattern and cortical source solutions. As such, they must be clearly distinguished from interictal epileptiform discharges in patients with epilepsy. SIGNIFICANCE: The awareness of these peculiar EEG characteristics may increase our ability to differentiate SSS from interictal epileptiform activity. The finding of a posterior insular source might serve as an inspiration for new physiological considerations regarding these enigmatic waveforms.     

Ictal Behaviors During Nonepileptic Seizures Differ in Patients with Temporal Lobe Interictal Epileptiform EEG Activity and Patients Without Interictal Epileptiform EEG Abnormalities

Summary: Purpose: Ictal behaviors during psychogenic non-epileptic seizures (NES) vary considerably among individuals, and can closely resemble common semiologies of epileptic seizures (ES). We tested the hypothesis that behaviors during NES in patients who have temporal spikes would more closely resemble behaviors during ES in patients with temporal lobe epilepsy than would behaviors during NES in patients who do not have EEG spikes.
Methods: We identified 20 patients who had interictal temporal EEG spikes and EEG-video recorded NES (Study Group), 133 patients with temporal EEG spikes and recorded ES, without NES (Epileptic Group), and 24 patients with recorded NES and no epileptiform EEG abnormalities, without ES (Nonepileptic Group).
Results: The hypothesis was supported with regard to ictal motor behaviors. Motionless staring or complex automatisms occurred mainly during NES in the Study Group and during ES in the Epileptic Group. In contrast, convulsive movements or flaccid falls were most common during NES in the Nonepileptic Group. Duration of unresponsiveness was longer, and there were fewer postictal states in NES both in the Study and Non-epileptic Groups. Unresponsiveness was briefer and postictal states were more consistent in ES in the Epileptic Group, however.
Conclusions: Stereotyped motor activities during NES presumably represent learned behaviors. Processes underlying acquisition of ictal behaviors of NES probably differ in patients with interictal epileptiform EEG abnormalities compared to those without. Prior experiences and temporal lobe dysfunctions that are associated with epilepsy, and psychological characteristics that are unrelated to interictal epileptic dysfunctions, may determine ictal behaviors during NES.     

Effect of barbiturate on epileptiform activity: comparison between intravenous and oral administration

The present study was performed in order to compare: 1) the differences between oral and intravenous barbiturate on interictal epileptiform activity (sharp-waves and spikes) in the EEG, and 2) interictal epileptiform activity in the sphenoidal electrode compared to the temporal and zygomatic electrodes (an electrode placed at the cutaneous entry of the sphenoidal electrode) during intravenous barbiturate administration in patients with epilepsy. Two procedures were performed: 1) an oral pentobarbital sleep induction with 10–20 electrode placement including a zygomatic electrode, and 2) an intravenous thiopental sleep induction with the same electrode placement including a sphenoidal electrode. Thirty eight patients with complex partial seizures were included. During the oral pentobarbital procedure 34 of 38 (90%) patients showed interictal epileptiform activity compared with 22 of 38 (55%) patients during the intravenous thiopental procedure (p<0.005). A interictal epileptiform focus was observed in 33 (87%) patients in the oral procedure and in 19 (50%) patients in the intravenous procedure (p<0.01). Interictal epileptiform activity recorded in the sphenoidal electrode was also recorded in the zygomatic electrode. Except from two patients a good correlation was observed between the zygomatic electrodes and the F7/F8 electrodes. We conclude that administration of intravenous thiopental offers no advantage compared to the administration of oral pentobarbital as an activating procedure, and for standard interictal EEG recordings with sleep activation procedures, suitable places scalp electrodes including a zygomatic electrode with the use of oral pentobarbital may be sufficient.     

Presurgical electroencephalographic patterns and outcome from anterior temporal lobectomy.

We reviewed data from 48 patients after anterior temporal lobe resection for medically intractable epilepsy. All had ictal electro-encephalographic (EEG) evidence of unilateral temporal lobe onset. Depth electrodes were used in 19 patients. Successful surgical outcome correlated significantly with factors that suggested a temporal lobe focus, particularly in the interictal scalp EEG. The most successful outcome occurred in patients with well-localized unilateral interictal temporal spikes (100% improved). The group with well-localized bilateral temporal spikes also did well (76% improved). Patients with extratemporal spread of the interictal spike on scalp EEG, either unilaterally or bilaterally, did less well. Only one third improved, despite extensive extracranial and intracranial monitoring, when indicated. The interictal scalp EEG may be the only EEG necessary for the presurgical evaluation of selected patients with intractable temporal lobe epilepsy.     

Interictal MEG/MSI in intractable mesial temporal lobe epilepsy: Spike yield and characterization

ObjectiveTo evaluate the ability of MEG to detect medial temporal spikes in patients with known medial temporal lobe epilepsy (MTLE) and to use magnetic source imaging (MSI) with equivalent current dipoles to examine localization and orientation of spikes and their relation to surgical outcome.MethodsWe prospectively obtained MSI on a total of 25 patients previously diagnosed with intractable MTLE. MEG was recorded with a 275 channel whole-head system with simultaneous 21-channel scalp EEG during inpatient admission one day prior to surgical resection. The patients’ surgical outcomes were classified based on one-year follow-up after surgery.ResultsNineteen of the 22 patients (86.4%) had interictal spikes during the EEG and MEG recordings. Thirteen of 19 patients (68.4%) demonstrated unilateral temporal dipoles ipsilateral to the site of surgery. Among these patients, five (38.5%) patients had horizontal dipoles, one (7.7%) patient had vertical dipoles, and seven (53.8%) patients had both horizontal and vertical dipoles. Sixty percent of patients with non-localizing ictal scalp EEG had well-localized spikes on MSI ipsilateral to the side of surgery and 66.7% of patients with non-localizing MRI had well-localized spikes on MSI ipsilateral to the side of surgery. Concordance between MSI localization and the side of lobectomy was not associated with a likelihood of an excellent postsurgical outcome.ConclusionsMSI can detect medial temporal spikes. It may provide important localizing information in patients with MTLE, especially when MRI and/or ictal scalp EEG are not localizing.SignificanceThis study demonstrates that MSI has a good ability to detect interictal spikes from mesial temporal structures.     

Bilateral mesial temporal lobe epilepsy: comparison of scalp EEG and hippocampal MRI-T2 relaxometry

OBJECTIVE: Bilateral hippocampal abnormality is frequent in mesial temporal lobe sclerosis and might affect outcome in epilepsy surgery. The objective of this study was to compare the lateralization of interictal and ictal scalp EEG with MRI T2 relaxometry. MATERIAL AND METHODS: Forty-nine consecutive patients with intractable mesial temporal lobe epilepsy (MTLE) were studied with scalp EEG/video monitoring and MRI T2 relaxometry. RESULTS: Bilateral prolongation of hippocampal T2 time was significantly associated with following bitemporal scalp EEG changes: (i) in ictal EEG left and right temporal EEG seizure onsets in different seizures, or, after regionalized EEG onset, evolution of an independent ictal EEG over the contralateral temporal lobe (left and right temporal asynchronous frequencies or lateralization switch; P = 0.002); (ii) in interictal EEG both left and right temporal interictal slowing (P = 0.007). Bitemporal T2 changes were not, however, associated with bitemporal interictal epileptiform discharges (IED). Lateralization of bilateral asymmetric or unilateral abnormal T2 findings were associated with initial regionalization of the ictal EEG in all but one patient (P < 0.005), with lateralization of IED in all patients (P < 0.005), and with scalp EEG slowing in 28 (82,4%) of 34 patients (P = 0.007). CONCLUSION: Our data suggest that EEG seizure propagation is more closely related to hippocampal T2 abnormalities than IED. Interictal and ictal scalp EEG, including the recognition of ictal propagation patterns, and MRI T2 relaxometry can help to identify patients with bitemporal damage in MTLE. Further studies are needed to estimate the impact of bilateral EEG and MRI abnormal findings on the surgical outcome.     

Is ictal recording mandatory in temporal lobe epilepsy? Not when the interictal electroencephalogram and hippocampal atrophy coincide

OBJECTIVE: To investigate the concordance between scalp electroencephalogram (EEG) lateralization and side of hippocampal atrophy in patients with temporal lobe epilepsy (TLE). METHODS: We studied 184 consecutive patients with TLE without lesions other than those compatible with mesial temporal sclerosis. In this study, we studied specifically hippocampal atrophy and the results of scalp EEG investigation. Patients were classified according to the localization of interictal epileptiform discharges as unilateral, bilateral asymmetric, and bilateral symmetric. The EEG seizure onsets were also classified separately as unilateral, bilateral asymmetric, and bilateral symmetric. The hippocampal atrophy was determined by volumetric measurements using high-resolution magnetic resonance imaging (MRIVol). RESULTS: Only 3% of patients had discordance between the ictal and interictal EEG lateralizations; however, none of these had unilateral interictal EEG abnormalities. Interictal EEGs were considered unilateral in 62.0% of patients, bilateral asymmetric in 31.5%, and bilateral symmetric in 6.5%. Ictal EEGs were considered unilateral in 63.5% of patients, bilateral asymmetric in 30.0%, and bilateral symmetric in 6.5%. The MRIVol showed unilateral hippocampal atrophy in 60.9% of patients, bilateral asymmetric hippocampal atrophy in 19.0%, symmetric hippocampal atrophy in 3.8%, and normal volumes in 16.3%. There was a significant concordance between MRIVol lateralization and both interictal and ictal EEG lateralization (P<.001). All patients with unilateral hippocampal atrophy had concordant interictal and ictal EEG lateralization. Six (18.2%) of the 33 patients with bilateral asymmetric hippocampal atrophy had MRI lateralization discordant with EEG lateralization. CONCLUSIONS: We found a strong concordance between EEG and MRIVol lateralization in patients with TLE. Unilateral hippocampal atrophy predicted ipsilateral interictal epileptiform abnormalities and ipsilateral seizure onsets with no false lateralization. Previous studies in addition to the present series support that a concordant outpatient EEG evaluation in patients with TLE and unilateral hippocampal atrophy would obviate the need for inpatient EEG monitoring.