Learn how to interpret and use intracranial EEG findings.

Epilepsy surgery is the therapy of choice for many patients with drug-resistant focal epilepsy. Recognizing and describing ictal and interictal patterns with intracranial electroencephalography (EEG) recordings is important in order to most efficiently leverage advantages of this technique to accurately delineate the seizure-onset zone before undergoing surgery. In this seminar in epileptology, we address learning objective "1.4.11 Recognize and describe ictal and interictal patterns with intracranial recordings" of the International League against Epilepsy curriculum for epileptologists. We will review principal considerations of the implantation planning, summarize the literature for the most relevant ictal and interictal EEG patterns within and beyond the Berger frequency spectrum, review invasive stimulation for seizure and functional mapping, discuss caveats in the interpretation of intracranial EEG findings, provide an overview on special considerations in children and in subdural grids/strips, and review available quantitative/signal analysis approaches. To be as practically oriented as possible, we will provide a mini atlas of the most frequent EEG patterns, highlight pearls for its not infrequently challenging interpretation, and conclude with two illustrative case examples. This article shall serve as a useful learning resource for trainees in clinical neurophysiology/epileptology by providing a basic understanding on the concepts of invasive intracranial EEG.

Single-center long-term results of vagus nerve stimulation for pediatric epilepsy: a 10-17-year follow-up study.

PURPOSE: A retrospective study, based on a prospectively built database, presents the results of long-term follow-up care of pediatric vagus nerve stimulation (VNS) patients in terms of seizure outcome, surgical aspects, the potential impact of maturation, and medication changes. METHODS: From a prospectively built database, 16 VNS patients (median age 12.0 years, range 6.0 to 16.0 years; median seizure duration 6.5 years, range 2.0 to 15.5 years) followed for at least 10 years were graded as non-responder - NR (seizure frequency reduction < 50%), responder - R (reduction ≥ 50% and < 80%), and 80% responder - 80R (reduction ≥ 80%). Data about surgical aspects (battery replacement, system complications), seizure dynamics, and medication changes were taken from the database. RESULTS: The early percentages of good results (80R + R) were 43.8% (year 1), 50.0% (year 2), and 43.8% (year 3). These percentages remained stable between years 10 and 12 (50% year 10; 46.7% year 11; 50% year 12) and increased in years 16 (60%) and 17 (75%). Depleted batteries were replaced in ten patients, six of whom were either R or 80R. In the four NR, the indication for replacement was improved quality of life. Three patients had VNS explanted or switched off-one had repeated asystolia and two were NR. The effect of hormonal changes in menarche on seizure was not proven. During the study, antiseizure medication was changed in all patients. CONCLUSIONS: The study proved the efficacy and safety of VNS in pediatric patients over an exceptionally long follow-up period. The demand for battery replacements indicates a positive treatment effect.

[Pharmacoresistant epilepsy after craniocerebral injury]. / Farmakorezistentní epilepsie po kraniocerebrálním poranení.

INTRODUCTION: Posttraumatic epilepsy is one of the possible serious consequencies of both closed and open head injury with clinical manifestation months or years after surgery. In pharmacoresistant patients, surgical therapy should be considered. MATERIAL AND METHODS: The study summarises the results of surgical treatment of pharmacoresistant posttraumatic epilepsy in a group of 13 patients (11 males and 2 females). Average age at the time of injury was 9.6 years in males and 8.8 years in females. The average number of seizures was 10.7-17 seizures/month preoperatively. Invasive EEG monitoring was required in 5 patients in whom non invasive or semiinvasive investigations failed to localize the epileptogenic zone adequately. Temporal lobe resections were performed in 4 patients, 4 patients underwent extratemporal resections and vagus nerve stimulation system was implanted in 5 patients. RESULTS: Three patients (75%) after temporal resections became seizure free (Engel I) and in the remaining patient significant reduction of seizures was achieved (Engel III). There were 2 seizure free patients after extratemporal resections (50%) and significant reduction of seizure rates was achieved (Engel III) in the remaining two. One patient after vagus nerve stimulation met the criteria for > 90% response and there was a 50-90% seizure rate reduction in the remaining 4 patients (vagus nerve stimulation responder). CONCLUSIONS: Although in limited group of patients the study confirms good results of surgical treatment of selected posttraumatic epilepsy patients--mainly temporal epilepsy patients and patients after vagus nerve stimulation. Meticulous presurgical evaluation including invasive encephalography in indicated patients is a precondition for surgical success.

Occurrence and lateralizing value of "rare" peri-ictal vegetative symptoms in temporal lobe epilepsy.

We retrospectively investigated rare peri-ictal vegetative symptoms (PIVS) in 380 seizures of 97 patients with temporal lobe epilepsy (TLE): 234 seizures of 60 patients with TLE with mesiotemporal sclerosis (TLE/MTS) and 146 seizures of 37 patients with TLE with other lesions (TLE/non-MTS) who were at least 2 years after epilepsy surgery and classified as Engel I. We assessed the following PIVS: peri-ictal cough (pC), peri-ictal water drinking (pWD), peri-ictal vomiting (pV), and peri-ictal spitting (pS). We observed pC in 24.7% of patients and 10% of seizures; pWD in 14.4% of patients and 5.9% of seizures; pV and pS occurred more rarely. Both pWD and pC occurred significantly more often in those with TLE of the non- language-dominant hemisphere. The limited occurrence of pV and pS made it impossible to perform statistical analysis for these symptoms. In patients with TLE, pC and pWD were quite frequent; we observed pV and pS less frequently. Both pC and pWD have a significant lateralizing value in TLE.

Lateralized ictal immobility of the upper limb in patients with temporal lobe epilepsy.

The primary aim of this study was to establish the incidence and the lateralizing value of 'lateralized ictal immobility of the upper limb' (LIL) in patients suffering from temporal lobe epilepsy (TLE), and to describe the connection between LIL and other clinical ictal signs. We retrospectively reviewed video records of 87 patients with TLE. We reviewed a total of 276 focal epileptic seizures with or without secondary generalization. We studied the incidence of LIL, its lateralizing value, and its relationship to other ictal clinical signs. Of the 87 patients, 49 had undergone a successful resective surgery at least 1 year prior to the study. LIL is a late sign in the course of partial seizure. It occurred in 25 of our 87 patients (28.7%), and in 47 of 276 seizures (17.1%). In all of the evaluated seizures, LIL occurred contralateral to the side of seizure onset (P < 0.001). LIL was always associated with ipsilateral upper limb automatisms, and in 63.1% of the occurrences, it was immediately followed by ictal dystonia. LIL is a more accurate term to describe what has previously been called 'ictal paresis' in the literature. Due to the inability to execute proper testing during a partial seizure, it is better to use the term LIL when making a visual analysis of a seizure. LIL is a more suitable term to describe the studied ictal sign. It is a relatively frequent sign in patients with TLE. LIL has an excellent lateralizing value for the contralateral hemisphere. It is a negative motor sign, and its genesis is probably associated with the epileptic involvement of the contralateral frontal lobe.

Ictal limb dystonia in temporal lobe epilepsy. an invasive video-EEG finding.

The aim of the investigation was to evaluate the ictal EEG in the putamen and the temporal and frontal lobes during contralateral ictal limb dystonia (ID). Ten epilepsy surgery candidates participated in the study. All of them were investigated using intracerebral and/or subdural electrodes. In four of the patients, the putamen was investigated with diagonal depth electrodes (patients 1-4), in six of the patients, both the temporal and frontal lobes were investigated (patients 5-10). All of the investigated contacts were located contralateral to the side of the ictal dystonia. All of the patients suffered from temporal lobe epilepsy (TLE); in patient 10, both temporal and frontal seizure types were recorded. A total of 20 complex partial seizures (CPS) were analysed. ID was never an early symptom in the course of CPS. Slow activity was recorded in the putamen in all 10 seizures of the four patients in whom the putamen was investigated (patients 1-4). In five of these seizures, there was a time-locked change in the ictal EEG in relation to the ID (slowing of activity in three seizures; acceleration in two seizures). At the time of the onset of ID, several cortical regions were involved in the ictal discharge, within both the contralateral temporal and frontal lobes. In all 10 seizures of the six patients in whom both the temporal and frontal lobes on the contralateral side were evaluated (patients 5-10), the ictal paroxysmal discharge was noted in both lobes (i.e. frontal and temporal) at the time of ID onset. We can conclude that ID is a late symptom in TLE. Widespread activation of the contralateral temporal and frontal lobes is needed for the appearance of ID; however, the critical region responsible for the genesis of ID was not revealed. Although there are some non-specific changes in the putamen contralateral to ID, the changes were never epileptic in type. The putamen probably collaborates in the genesis of ID, but it does not generate the epileptic discharge during its course.

A SEEG study of ERP in motor and premotor cortices and in the basal ganglia.

OBJECTIVE: Our intention was to study the electrical activity related to the cognitive processing of simple sensory stimuli in the brain structures that participate in motor control. We focused our interest on the 250-600 ms time window, in which cognitive activity most probably provides the basis for the activity recorded. METHODS: Intracerebral stereoelectroencephalography (SEEG) recordings were made from 15 epilepsy surgery candidates. We studied potentials that were recorded in a time window in which P300 usually could be recorded on the scalp and that were directly recorded from brain structures involved in motor control: the primary motor cortex (MC, Brodmann's area 4); the lateral and mesial (SMA) premotor cortices (Brodmann's area 6); and the basal ganglia. We evaluated the first distinctive potential to occur in the 250-600 ms time window that displayed an amplitude gradient in several adjacent contacts. Four protocols were performed: an auditory oddball (aP3); a visual oddball (vP3); and contingent negative variation (CNV) protocols, in which the potentials evoked by the auditory warning (aCNV) and visual imperative (vCNV) stimuli were evaluated. In the protocols aP3, vP3, and vCNV, the tested person responded by flexing his/her thumb or hand. In the aCNV paradigm, and in a further auditory oddball paradigm (aP3c), no motor response was required. We compared the presence of an event-related potential (ERP) with an amplitude gradient to the absence of a generator. RESULTS: The frequency of P3-like potential components was statistically significantly higher in the basal ganglia when compared with the explored cortical sites. Statistically non-significant latency differences between the basal ganglia and the cortex were displayed. The differences in the distribution of the potentials in the individual cortical areas were insignificant. The mean latency of vP3 was longer than the latencies of aP3, aP3c and vCNV. There was no significant difference between the distribution and latency of aP3 and aP3c. CONCLUSIONS: (1) ERPs are generated in cortical as well as in subcortical structures. (2) The cognitive processing of sensory information in all the tested protocols occurred in the basal ganglia; the occurrence in the investigated cortical areas was less frequent and more dependent on the task. The basal ganglia may play an integrative role in cognitive information processing, in motor and non-motor tasks.