Amiram Katz

Morphological Patterns of Seizures Recorded Intracranially

Summary: We analyzed the frequency and morphological characteristics of the initial EEG manifestations of spontaneous seizures recorded from depth and subdural electrodes in 26patients for whom pathological analysis of the area of seizure onset was available after resective surgery. Pathological features considered to be positive findings included well‐defined structural lesions (hamartoma, neoplasm) or strictly defined mesial temporal sclerosis. Seizure onset was characterized by the frequency of the rhythmic discharge >2 Hz in the first second and by the presence or absence of periodic low‐frequency spikes (<2 Hz) preceding this stable change in background frequency. These features were correlated with the presence or absence of pathologic abnormalities in temporal and extratemporal locations. Although all patterns and frequencies of seizure onset were recorded in both medial temporal and extratemporal locations, medial temporal seizure onset was significantly more likely to have high frequency (>13 Hz, p < 0.05) and no periodic spikes before seizure onset tended to periodic spikes prior to the seizure when it was associated with medial temporal sclerosis compared to when it was not. Extratemporal seizure onset associated with abnormal pathological substrate was significantly more likely to have a lower frequency (<13 Hz, p < 0.05) and no periodic spikes before seizure onset (p < 0.00001) than extratemporal seizure onset recorded from areas without pathological findings. Variability of seizure onset frequency was a characteristic of temporal, but not extra temporal, seizures (p < 0.01). The existence of such differences between seizures of temporal and extratemporal origin suggests that the underlying anatomy may in part determine these patterns, and that interpretation of EEG records of seizures beginning in different cerebral locations requires recognition of these differences.

Does interictal spiking change prior to seizures

We studied 10 patients with intractable epilepsy being evaluated for epilepsy surgery for preictal changes in spiking. All patients were implanted with intracranial electrodes and underwent continuous EEG/audiovisual monitoring. Interictal spikes were detected and recorded continuously by a dedicated computerized system. Edited spikes were counted during 0-5, 5-10, and 0-60 min epochs before each seizure, during epochs of unvarying state of arousal (awake or sleep stage II). When comparing by repeated measures, 1-way ANOVA, total spiking (in all recording channels) did not differ among the different preictal epochs (0-5, 5-10, 0-60 min) in 45 seizures (F = 0.88, P = 0.40, using the Geisser-Greenhouse adjustment--GGA). Likewise, no significant differences were obtained during those same epochs when comparing spiking originating from the channel of seizure onset in 5 patients with 28 seizures of localized onset (F = 1.19, P = 0.38 using the GGA). Our findings indicate that in patients with intractable epilepsy, no changes in spiking occur in the 5 min prior to seizures, when compared to more distant preictal epochs.

Frontal lobe partial seizures and psychogenic seizures Comparison of clinical and ictal characteristics

Of all partial seizures, those of frontal lobe origin (FLPS) are most bizarre and are often mistaken for psychogenic seizures (PS). The reverse can also be true. To clarify the confusing clinical presentation of these different seizure types, we compared the clinical ictal characteristics of 63 FLPS in 11 patients with 29 PS in 12 patients. Patients with PS had significantly later age at onset and longer ictal duration. There was no statistically significant difference between the two groups with respect to history of psychiatric disorder, ictal pelvic thrusting, rocking of body, side-to-side head movements, or rapid postictal recovery, all of which previously have been reported as characteristic features of PS. Turning to a prone position during the seizure occurred only in FLPS. Nocturnal occurrence, short ictal duration, younger age at onset, stereotyped patterns of movements, and MRI and EEG abnormality suggested FLPS.

Direct Measurement of Extracellular Lactate in the Human Hippocampus During Spontaneous Seizures

Abstract: The effect of clinical, spontaneous‐onset seizures on extracellular fluid lactate was investigated by the method of lactography, the in vivo on‐line measurement of lactate levels using microdialysis. Studies of experimental animals have suggested that generation of extracellular lactate as measured by microdialysis is an index of local glucose utilization and is dependent on the activity of neurons under physiological conditions. Patients with medically refractory complex partial epilepsy underwent stereo‐tactic implantation of combination depth electrode/micro‐dialysis probes into both hippocampi for 7–16 days. During spontaneous complex partial seizures with secondary generalization, extracellular lactate levels rose by 91 β 32%. Moreover, this increase persisted for 60–90 min. During a unilateral hippocampal seizure that did not propagate to the contralateral hippocampus, the increase in lactate content was restricted to the side of seizure activity. Between seizures, extracellular lactate levels correlated with the frequency of interictal spikes. In summary, these data suggest that brief clinical seizures increase nonoxidative glucose metabolism significantly as measured by the generation of extracellular lactate. Furthermore, the increase in extracellular lactate level is limited to the site of seizure activity. Lactate is transported extracellularly via a lactate/proton cotransporter; therefore, the rise in extracellular lactate level may mediate the drop in pHo associated with seizure activity. As acidification of the extracellular compartment has an inhibitory effect on neuronal excitability, the rise in extracellular lactate content may be a mechanism of seizure arrest and postictal refractoriness. Moreover, extracellular lactate may also mediate the decreased seizure susceptibility associated with frequent interictal spikes.

Anterior, Total, and Two‐Stage Corpus Callosum Section: Differential and Incremental Seizure Responses

Summary: Published reports suggest that control of generalized seizures is improved by callosotomy but do not necessarily indicate that completion of failed anterior callosotomy is beneficial. We studied 42 patients after anterior callosotomy and 22 after total callosotomy, of whom 14 underwent a two‐stage procedure. Cure or marked diminution of seizures was most dramatic for atonic and tonic‐clonic seizures after anterior callosotomy (100 and 83%), and for tonic‐clonic and tonic seizures after total callosotomy (68 and 57%). For the 14 patients who failed to improve after anterior section and then underwent total section, incremental responses were noted for all seizure types, with cure or marked diminution of partial seizures in 2 of 14 patients, of tonic‐clonic seizures in 6 of 10, of tonic seizures in 2 of 4, of atonic seizures in 2 of 5, and of myoclonic seizures in 1 of 1. More than two seizure types, verbal IQ <80, and diffuse ictal EEG patterns were significantly more common in the anterior callosotomy failures. Total callosotomy can be of benefit when anterior callosotomy fails, especially for persistent tonic‐ clonic and tonic seizures, and will most often be necessary in patients with diffuse cerebral abnormalities.

Comparison and correlation of surface and sphenoidal electrodes with simultaneous intracranial recording: an interictal study

We prospectively compared and correlated interictal spikes recorded with simultaneous surface, sphenoidal, depth and subdural electrodes in 21 patients. Although the amplitude of sphenoidal spikes was often larger than that of surface spikes in patients with mesial basal temporal ictal and interictal foci, only 1 patient had exclusively sphenoidal spikes. Spikes with maximal amplitude at the sphenoidal electrode arose from mesial temporal, temporal neocortical and orbital frontal foci. An inferior vertical temporal dipole (hippocampal positive and inferior temporal neocortex negative) was associated with surface and sphenoidal spikes.

Anatomic Correlates of Interhippocampal Seizure Propagation Time

Summary: The relation between interhippocampal seizure propagation time (IHSPT) and anatomic alterations in the human epileptic hippocampus may provide insight into the pathophysiology of temporal lobe epilepsy (TLE). Using depth electrode recordings, we measured the time required for spontaneous seizures with onset in one hippocampus to become manifest in the contralateral hippocampus in 50 patients who underwent resection of the temporal lobe of seizure origin. Cell densities in individual hippocampal subfields were determined and correlated with mean IHSPT for each patient. Mean IHSPT was significantly and inversely correlated with cell counts in CA4 only (r =−0.38, p < 0.01, Pearsons product correlation; r =−0.52, p < 0.001, Spearmans rank order correlation). In 5 patients with bilateral independent hippocampal seizure onset who had temporal lobectomy and a diagnosis of mesial temporal sclerosis, mean IHSPT was consistently longer from the sclerotic temporal lobe than to it. These observations suggest that anatomic changes associated with chronic epilepsy alter propagation patterns. Because CA4 is believed to modulate the output of dentate granule cells and also has commissural connections to the contralateral homotopic area, the association of decreased CA4 cells with prolongation of IHSPT suggests that the observed anatomic alterations may actively (through increased inhibition) or passively (through decreased recruitment) interfere with various routes of seizure propagation.

Clinical and electrographic effects of acute anticonvulsant withdrawal in epileptic patients

We retrospectively investigated the effects of acute antiepileptic drug (AED) withdrawal on seizure symptomatology—including frequency, clinical features, and electrical onset—by studying 35 patients during evaluation for epilepsy surgery. The highest risk for both partial and secondary generalized seizures occurred during absent or subtherapeutic, and not during rapidly falling, AED levels. AED withdrawal had minimal effect on clinical symptomatology or electrographic onset.

Differentiation of temporal lobe ictal behavior associated with hippocampal sclerosis and tumors of temporal lobe.

Summary: Ictal behavioral characteristics may reflect seizure spread patterns and provide a clue to seizure onset location, between or within specific cerebral lobes. Sequential symptomatology might therefore distinguish patients with hippocampal sclerosis from patients with temporal lobe tumors. To determine ictal behavioral differences in patients of these groups, we analyzed 145 seizures of 33 patients with hippocampal sclerosis (group I) and 79 seizures of 22 patients with temporal lobe tumors (group 11). First appearance of a variety of ictal behavioral characteristics was determined in three phases (first 5 s, 5–60 s, and from 60 s to mental clearing) for patients in both groups. Ipsilateral hand automatisms were significantly more frequent in the first 60 s in group I (p < 0.005). Onset of contralateral head turning was observed in the first 5 s only in group Il (p < 0.05). First appearance of leg automatisms in group I and of oral automatisms in group Il were very rare in phase 2 (p < 0.01, p < 0.005). Time of onset of other ictal behavioral characteristics and duration of seizures were not statistically different between the two groups. Ictal behavioral characteristics varied among and within patients and patient groups, but certain behavioral characteristics were helpful in differentiating these two groups of temporal lobe epilepsy (TLE) patients.

SPECT in patients with epilepsia partialis continua

We report 2 patients with epilepsia partialis continua (EPC) in whom ictal single photon emission computed tomography (SPECT) showed focal increased signal while EEG failed to show epileptic changes. SPECT may clarify confusing situations when EPC is suspected.