Clinical and electroencephalographic evidence for sites of origin of seizures with diffuse electrodecremental pattern

Is High-Frequency Activity at Seizure Onset Inhibitory? A Stereoelectroencephalographic Study of Motor Cortex Seizures

OBJECTIVE

In the era of stereoelectroencephalography (SEEG), many studies have been devoted to understanding the role of interictal high-frequency oscillations. High-frequency activity (HFA) at seizure onset has been identified as a marker of epileptogenic zone. We address the physiological significance of ictal HFAs and their relation to clinical semiology.

METHODS

We retrospectively identified patients with pure focal primary motor epilepsy. We selected only patients in whom SEEG electrodes were optimally placed in the motor cortex as confirmed by electrical stimulation. Based on these narrow inclusion criteria, we extensively studied 5 patients (3 males and 2 females, mean age = 22.4 years) using time-frequency analysis and time correlation with motor signs onset.

RESULTS

A total of 157 analyzable seizures were recorded in 5 subjects. The first 2 subjects had tonic or clonic semiology with rare secondary generalization. Subject 3 had atonic onset followed by clonic hand/arm flexion. Subject 4 had clusters of tonic and atonic facial movements. Subject 5 had upper extremity tonic movements. The median frequency of the fast activity extracted from the Epileptogenic Zone Fingerprint pipeline in the first 4 subjects was 76 Hz (interquartile range = 21.9Hz). Positive motor signs did not occur concomitantly with high gamma activity developing in the motor cortex. Motor signs began at the end of HFAs.

INTERPRETATION

This study supports the hypothesis of an inhibitory effect of ictal HFAs. The frequency range in the gamma band was associated with the direction of the clinical output effect. Changes from inhibitory to excitatory effect occurred when discharge frequency dropped to low gamma or beta. ANN NEUROL 2024;95:1127-1137.

Seizure initiation in infantile spasms vs. focal seizures: proposed common cellular mechanisms

Infantile spasms (IS) and seizures with focal onset have different clinical expressions, even when electroencephalography (EEG) associated with IS has some degree of focality. Oddly, identical pathology (with, however, age-dependent expression) can lead to IS in one patient vs. focal seizures in another or even in the same, albeit older, patient. We therefore investigated whether the cellular mechanisms underlying seizure initiation are similar in the two instances: spasms vs. focal. We noted that in-common EEG features can include (i) a background of waves at alpha to delta frequencies; (ii) a period of flattening, lasting about a second or more - the electrodecrement (ED); and (iii) often an interval of very fast oscillations (VFO; ~70 Hz or faster) preceding, or at the beginning of, the ED. With IS, VFO temporally coincides with the motor spasm. What is different between the two conditions is this: with IS, the ED reverts to recurring slow waves, as occurring before the ED, whereas with focal seizures the ED instead evolves into an electrographic seizure, containing high-amplitude synchronized bursts, having superimposed VFO. We used in vitro data to help understand these patterns, as such data suggest cellular mechanisms for delta waves, for VFO, for seizure-related burst complexes containing VFO, and, more recently, for the ED. We propose a unifying mechanistic hypothesis - emphasizing the importance of brain pH - to explain the commonalities and differences of EEG signals in IS versus focal seizures.

Stimulus-induced diffuse voltage attenuation (SIDVA): a previously undescribed EEG pattern in a critically ill child

We report the case of a 15-month-old critically ill child with stimulus-induced diffuse voltage attenuation, a previously unreported electroencephalogram pattern. No clinical evidence of seizure activity was associated with these EEG changes. The patient went on to have a full recovery. This case suggests that critically ill children have distinct stimulus induced electrographic patterns from those seen in adults. Additional research is needed to define the significance of these patterns.

Proven startle-provoked epileptic seizures in childhood: semiologic and electrophysiologic variability

PURPOSE

To delineate further the clinical and electrophysiologic features of proven startle-provoked epileptic seizures (SPESs) in children.

METHODS

Clinical, neuroradiologic, and neurophysiologic data of 22 consecutive patients with SPESs were analyzed. Eighty-nine SPESs were documented by video-EEG and evaluated with respect to semiology and ictal and interictal EEG findings.

RESULTS

Mean age was 68 months (10-178 months). Most children had severe mental retardation (86%). Neuroimaging demonstrated diffuse cerebral abnormalities in 15 of 19. Somatosensory evoked potentials revealed cortical abnormalities in 10 of 13 children. The underlying causes were heterogeneous. Only two patients were normally developed. Seizure frequency was usually high (>10/day). Two children had less frequent SPESs (two per month; two per week). Seizures were easily precipitated by sudden sound (n=15), unexpected touch (n=3), or both (n=4). The most common semiologic findings (50%) were generalized tonic seizures or those characterized by a predominant tonic phase, followed in frequency by myoclonic seizures (36%), which were generalized in seven, and unilateral in one. Generalized clonic seizures were observed in one. A complex seizure spread was documented in two children. The most common ictal EEG finding (60%) was a diffuse electrodecremental pattern (DEP). Generalized spike/polyspike waves were found in five and focal discharges in four.

CONCLUSIONS

Our results imply that startle epilepsy is not a uniform epileptic entity. We were able to demonstrate a number of distinct patterns of SPESs, characterized by clinical, semiologic, and electrophysiologic features. Considering the high diversity of SPES patients, a common underlying pathophysiologic mechanism seems unlikely.

Ictal Onset and Spreading of Seizures of Parietal Lobe Origin

The characteristics of seizures associated with parietal lobe epilepsy were investigated in six consecutive patients with medically intractable epilepsy due to parietal lobe lesions. Intracranial electrode recordings were retrospectively reviewed to investigate the seizure onset symptoms and spreading patterns associated with the disorder. All six patients underwent implantation of subdural or depth electrodes and subsequent video/electroencephalography monitoring. Common symptoms included motionless stare, contralateral eye deviation, and head turn. Tonic posturing, contralateral sensory disturbance, and motor weakness were also seen. Asymmetrical generalized tonic and clonic seizures were seen in all six patients. All seizure activities began in the parietal lobe harboring the lesions, and then spread immediately to the adjacent lobes in most seizures, where the clinical symptoms were produced. The parietal lobe is a pure generator of seizures, whereas most clinical symptoms originate from adjacent lobes following seizure onset. No apparent specific symptoms other than sensory disturbance arising from the parietal lobe proper were recognized. Regardless of clinical symptoms, the seizure onset occurred in the parietal lobe harboring the lesion.

Cooling abolishes neuronal network synchronization in rat hippocampal slices

PURPOSE

We sought to determine whether cooling brain tissue from 34 to 21 degrees C could abolish tetany-induced neuronal network synchronization (gamma oscillations) without blocking normal synaptic transmission.

METHODS

Intracellular and extracellular electrodes recorded activity in transverse hippocampal slices (450-500 microm) from Sprague-Dawley male rats, maintained in an air-fluid interface chamber. Gamma oscillations were evoked by afferent stimulation at 100 Hz for 200 ms. Baseline temperature in the recording chamber was 34 degrees C, reduced to 21 degrees C within 20 min.

RESULTS

Suprathreshold tetanic stimuli evoked membrane potential oscillations in the 40-Hz frequency range (n = 21). Gamma oscillations induced by tetanic stimulation were blocked by bicuculline, a gamma-aminobutyric acid (GABA)A-receptor antagonist. Cooling from 34 to 21 degrees C reversibly abolished gamma oscillations in all slices tested. Short, low-frequency discharges persisted after cooling in six of 14 slices. Single-pulse-evoked potentials, however, were preserved after cooling in all cases. Latency between stimulus and onset of gamma oscillation was increased with cooling. Frequency of oscillation was correlated with chamber cooling temperature (r = 0.77). Tetanic stimulation at high intensity elicited not only gamma oscillation, but also epileptiform bursts. Cooling dramatically attenuated gamma oscillation and abolished epileptiform bursts in a reversible manner.

CONCLUSIONS

Tetany-induced neuronal network synchronization by GABAA-sensitive gamma oscillations is abolished reversibly by cooling to temperatures that do not block excitatory synaptic transmission. Cooling also suppresses transition from gamma oscillation to ictal bursting at higher stimulus intensities. These findings suggest that cooling may disrupt network synchrony necessary for epileptiform activity.

The epileptic pre-aura

The term "pre-aura" is used for the designation of earliest pre-ictal manifestations that escape detection by conventional EEG and both objective and subjective behavioral signs. Fairly recent reports have indicated earliest pre-ictal vascular changes (perifocal ischemia and hyperemia) and also changes found in various methods of quantified EEG. These changes may precede the seizure onset (in conventional terms) by 1 to 20 minutes. There is good reason to assume that pre-auras are limited to focal epilepsies and do not occur in the various subforms of primary generalized epilepsy. The electrodecremental type of seizure onset, mostly found in the frontal region, could also denote a pre-aura in the earliest decremental phase. The very earliest pre-aura phenomena are most likely to be neuronal rather than vascular. Further proof could come with the use of ultrafast EEG frequency recordings.

Rasmussen encephalitis associated with segmental vitiligo of the scalp: clinicopathologic report

A 3-year-old boy with segmental vitiligo, poliosis, and alopecia over the right side of the scalp developed epilepsia partialis continua involving the left side of the body and progressive atrophy of the right cerebral hemisphere. There was a right ear dysacusia and a perilimbal vitiligo associated with an area of iris depigmentation in the right eye. Pleocytosis and hypergammaglobulin were detected in cerebrospinal fluid. Because medical treatment that included phenobarbital, phenytoin, carbamazepine, oxcarbazepine, benzodiazepines, corticosteroids, gamma-globulin, and a ketogenic diet was ineffective, he underwent a right hemispherectomy. Neuropathologic examination showed a widespread scattered inflammatory process with numerous microglial nodules and perivascular lymphocytic cuffing associated with degenerative changes with severe neuronal loss, loosening of the neuropil, and microcystic changes with tissue collapse. The coexistence of vitiligo and possibly Vogt-Koyanagi-Harada syndrome in this child reinforces the autoimmune theory as the pathogenesis of Rasmussen syndrome.

Nocturnal paroxysmal dystonia related to a prerolandic dysplasia

Nocturnal paroxysmal dystonia (NPD) is a rare disorder characterized by attacks of short-lived dystonic, tonic and choreoatetoid movements occurring mainly during sleep. Although seizures are believed to arise from the frontal lobe, their localization is, however, uncertain due to the lack of ictal clinical-EEG correlations. Two patients are reported with episodes clinically compatible with NPD who also experienced occasional generalized tonic-clonic seizures in which there was a frontal (prerolandic) dysplasia detected by MRI. In one patient interictal/ictal SPECTs suggested that the seizure focus was over the area of dysplasia. Both patients support the notion that NPD is a type of epilepsy arising from the frontal lobe, possibly originating in the prerolandic region.

Focal extratemporal epilepsy: clinical features, EEG patterns, and surgical approach

The objective of this review is a summary of the clinical and electrographic findings in those forms of epilepsy to which the term 'extratemporal' (ExT) can be applied. They form a group that differs in many ways from the better known temporal lobe epilepsies. Seizure foci are difficult to localize by clinical semiology alone but modern imaging now often allows a precise definition of the epileptogenic area. The most common causes of ExT epilepsy are tumors and cortical dysgenesis. The concept of 'dual pathology' implies the coexistence of two or more distinct lesions, typically mesial temporal sclerosis and cortical dysplasia. Electroencephalography (EEG) and electrocorticography (ECoG) are valuable tests in the definition of the epileptogenic area beyond the structural lesion, and surgical removal must be guided by the nature of the lesion and the extent of the epileptogenic zone.

Frontal lobe epilepsy: the next frontier

Frontal lobe epilepsy, the great new epileptological challenge, presents enormous difficulties that still preclude a more profound understanding at the present time. The major subdivision of the frontal lobe into a prefrontal and premotor portion is the first step toward a better and yet limited comprehension of the frontal lobe epilepsies. Prefrontal implies higher mental functions (e.g., ictal forced thinking); rapid generalization to full grand mal evolves quite often from prefrontal foci. The frontal accentuation of classical generalized 3/sec spike-wave absences adds to the conceptual difficulties of the frontal lobe epilepsies. The unique type of disturbed consciousness in classical absences is presumed to be based upon ictal "suspension of the working memory." Limbic components (via orbitofrontal and cingulate mechanisms) also play an important role. Correlations between ictal semiologies and regional frontal lobe functions are still quite controversial.