Abdorasool Janati

Correlative Study of Interictal Electroencephalogram and Aura in Complex Partial Seizures

Summary: To understand fürther relationships of the interictal electroencephalogram to the aura in complex partial seizures (CPS), we studied the interictal EEG and aura in 144 patients with CPS. The ages of the patients studied ranged from 31 to 80 years (average 52.44 years). The duration of seizures ranged from 1 to 60 years (average 15.69 years). Seventy patients (49%) reported auras which were classified according to the guidelines recommended by the Commission of the International League Against Epilepsy. Statistical analysis revealed no relationship between presence, laterality, or localization of EEG abnormality and the number or type of aura. The results emphasize that more factors than electrophysiologic localization alone participate in the détérmination of aura in CPS. Our data support the position that aura has, at most, a limited relationship to lateralization or localization of interictal cerebral dysfunction in CPS.

Positive temporal sharp waves in neonatal EEG.

The clinical correlates and EEG characteristics of rolandic positive sharp waves in neonatal EEG have been studied systematically. Morphologically similar positive sharp waves have been reported to occur in the temporal areas (PTS). Their significance is, however, unclear. We reviewed fifty-two EEGs on patients from the Neonatal Intensive Care Unit of the University of Arkansas for Medical Sciences. Twenty-one of the EEGs which were reviewed had PTS. We correlated the PTS with the results of ultrasound of the head and with clinical evaluations. PTS are more strongly correlated with the occurrence of non-hemorrhagic than of hemorrhagic intracranial pathology.

The Anterior Temporal Electrode in the EEG of the Adult

The anterior temporal cerebral region is not well covered, electroencephalographically, by the usual EEG electrodes. Numerous attempts have been made to add anterior temporal electrodes. There has been discussion regarding the amount of additional information actually attributable to those electrodes. We systematically evaluated the abnormalities revealed by one such noninvasive set of anterior temporal electrodes, D. Silvermans T1 and T2. A total of 624 consecutive EEGs were reviewed. We conclude that, in the adult, anterior temporal electrodes can add significantly to the information contained in the routine interictal EEG.

Clinical correlate of EEG rhythmicity.

The widespread use of the routine EEG in clinical practice was a major development in the treatment of patients with ill-defined spells thought to be epileptic. Not every finding on the EEG is suggestive of epilepsy, and the EEG is subject to overinterpretation, which may lead to misdiagnosis and incorrect treatment. Although supplemented by other procedures, the EEG remains a cost-effective and noninvasive way to diagnose spells. To enhance further the diagnostic use of the EEG, it is important to determine how strongly patterns are correlated with clinical seizures. The authors studied one EEG pattern, lateralized bursts of &thgr;, and found the rhythmicity of the pattern to be most strongly correlated with seizures.

Positive Sharp Waves in Neonatal EEG

ABSTRACT.The clinical correlates and EEG characteristics of rolandic positive sharp waves in neonatal EEG have been studied systematically. Morphologically similar positive sharp waves have been reported to occur in the temporal areas (PTS). Their significance is, however, unclear. We reviewed 52 EEGs on patients from the Neonatal Intensive Care Unit of the University of Arkansas for Medical Sciences. Twenty-one of the EEGs which were reviewed had PTS. We correlated the PTS with the results of ultrasound of the head and with clinical evaluations. PTS are more strongly correlated with the occurrence of nonhemorrhagic than of hemorrhagic intracranial pathology.

WAIS performance in epileptics with unilateral interictal EEG abnormalities

A predictable relationship between Verbal Comprehension deficits and EEG abnormalities in the left hemisphere of patients with focal and generalized seizures has been reported. A relationship has also been reported between Perceptual Organization deficits and right-hemisphere EEG abnormalities. To extend and verify these findings, the performance of the left- and right-hemisphere seizure groups were compared using multivariate analyses of variance on three factors of cognitive performance: Verbal Comprehension, Perceptual Organization, and Freedom from Distractibility. Twenty-eight right-handed male subjects with focal seizures lateralized to either the left or right hemisphere by EEG were studied using the Wechsler Adult Intelligence Scale. Our initial hypotheses that individuals with left-hemisphere seizure foci would perform significantly more poorly on Verbal Comprehension tasks and individuals with right-hemisphere seizure foci would perform significantly more poorly on Perceptual Organization tasks were not confirmed. The data suggest that theoretical bias may obscure the mechanism of cognitive dysfunction in epileptic populations.

Aberrant EEG rhythms and epilepsy.

To the Editor: In the erudite article by Sinha (2011) on relationship of sleep and epilepsy, the author noted that a common circuit has been postulated to be responsible for generation of sleep spindles and spike-wave complexes. However, this hypothesis can be disputed by clinical pathologic syndromes, where abnormal spindling has occurred in the absence of epileptiform discharges, signifying a possible dissociation of mechanisms underlying these two EEG patterns. In the study of EEG in thalamic tumors in children, Hirose et al. (1975) found spindle activity in waking over the ipsilateral hemisphere. However, despite this “aberrant spindling,” there was no documented epileptiform activity or clinical seizures. In another study, in an adult patient with hemispheric glioblastoma extending into the lateral thalamus and the posterior limb of the internal capsule (Janati and Hester, 1986), aberrant spindles occurred in waking ipsilaterally, whereas physiologic spindles disappeared in sleep over the same hemisphere. Again, no epileptiform discharges were found. Obviously, in both studies, a dynamic cerebral pathology (brain tumor) caused a disruption of synaptic pathways in the thalamus or thalamusecortexethalamus circuit, provoking the genesis of aberrant spindling but without inducing epileptiform discharges. Ripples (episodic focal beta), as described by the author, have been found to be associated clinically with epilepsy in the majority of cases reported in the literature (Hooshmand et al., 1980; Nealis and Duffy, 1978). They are often associated with an underlying cerebral pathology, particularly cerebral malformations (arteriovenous malformations and cerebral dysgenesis), porencephalic cysts, and brain tumors. In one study (Hooshmand et al., 1980), the episodic focal beta was considered to be an ictal pattern seen primarily in LennoxeGastaut syndrome and infantile spasms where electrodecremental seizures are also common. Whether ripples (episodic focal beta) and electrodecremental seizures (episodic generalized beta) share common pathophysiologic mechanisms is not clear. Although a cortical origin has been proposed for ripples, a brain stem pacemaker has been theorized for the genesis of electrodecremental seizures. It is therefore conceivable that subcortical pathways may also play a role in the pathogenesis of ripples. Sleep-induced physiologic variants resembling epileptiform discharges typically occur at specific stages of sleep (e.g., hypnagogic hypersynchrony and psychomotor variant in drowsiness, “mittens” in deep sleep), although the reason for such selectivity has not been determined. Therefore, future studies should consider the physiologic mechanisms and neuronal pathways involved in the generation of these variants to broaden the existing knowledge of sleep mechanisms. Moreover, similar studies should address the neuropathologic mechanisms of abnormal arousal patterns (e.g., paradoxical arousal) in relationship to different types of cerebral pathology and epileptic syndromes.

A correlative study of electroencephalography and computed tomography in partial complex seizures in adults

Abstract To further elucidate relationships between the EEG and computed tomography (CT) in partial complex seizures (PCS), we retrospectively reviewed the EEGs and CT scans in nonselected, predominantly male patients with refractory PCS. We further correlated EEG and CT results with clinical data. All 78 patients in the study had EEGs and CT scans. The time span between the two procedures was 6 months or less. The ages of the patients ranged from 25 to 80, with an average of 51 years. Seizure chronicity ranged from 1 to 60 years, with an average of 15 years. Statistical analysis revealed a trend for unilateral CT and EEG abnormalities to be on the same side. There was no significant relationship between the location of abnormalities on EEG and on CT. The greatest degree of disagreement between CT and EEG occurred in patients with normal findings or diffuse atrophy on CT. There was no significant difference in the age between groups defined by different EEG categories (normal, right-sided, left-sided, or bilateral). The average age of patients with bilateral CT lesions was greater than that of patients with other CT lesions. This observation may reflect the influence of aging rather than the epileptic process on CT findings in PCS. We conclude that surface EEG and neuroimaging measure complementary aspects of cerebral pathology in PCS.

Unilateral Alpha Rhythm and Cheyne-Stokes Respirations

A case of unilateral basal ganglion hemorrhage with Cheyne-Stokes respirations is presented. During the hyperpneic periods there was rhythmic alpha activity in the hemisphere contralateral to the basal ganglion hemorrhage. We postulate that the hemorrhage interrupted the thalamocortical fibers on the involved side. The implications of this clinical evidence are discussed in the light of the theory of cerebral autorhythmicity.

Interictal epileptiform discharges and epilepsy prediction.

To the Editor: I read with interest the article by Dr. So (2010) who, after an extensive review of the literature, concluded that the presence of interictal epileptiform discharges (IEDs) on the EEG carries a higher risk of “seizures” in patients with neurologic symptoms compared with healthy individuals with the same EEG pattern. Dr. So also asserts that the risk of “epilepsy” in patients with IEDs remains unknown. Controversy exists surrounding the correct definition of sharp waves and spikes. A definition that has consistently appeared in the literature is as follows: “distinct waves or complexes distinguishable from the background activity, and with a sharp configuration.” This definition, however, is ambiguous. A more objective definition was introduced years ago, at a symposium of the American Clinical Neurophysiological Society, as follows: “a waveform that is characterized by an amplitude of 2.5 times that of the underlying background with a duration of either less than 70 milliseconds (spikes) or longer than 70 milliseconds (sharp waves).” It should be noted that the terms sharp waves and spikes may not always be interchangeable in different clinical settings. For example, there have been anecdotal reports of a higher incidence of sharp waves rather than spikes in slowly growing lesions such as supratentorial tumors and in slowly progressive pathologic processes as observed in Alzheimer’s disease. Conceivably, the differences in the definitions applied to IEDs may have partly accounted for the discrepancies noted in the EEG literature. Also, the “negative afterdischarge” as a component of the IEDs and its amplitude may be an important parameter, deserving further investigation. Unlike sharp waves and spikes, “sharp slow waves” (to be distinguished from sharp wave complexes) have been vastly overlooked in the literature. Indications are that this pattern may have significant implications in connection with epilepsy diagnosis, cause, and severity. The presence of IEDs poses a serious concern in epilepsy legal defense when aggression or crime may be interpreted as a manifestation of epileptic mental automatisms in an otherwise healthy offender with or without a history of aggressive or criminal behavior. In such instances, where neurologists may be asked to testify as expert witnesses, circumstances surrounding the crime, a thorough medicolegal history, detailed clinical data, and a period of hospital-based observation with video-EEG monitoring are required to resolve the issue by establishing or refuting criminal liability. Finally, as Dr. So suggests, future studies of IEDs should eschew the “methodological shortcomings” of the past. Moreover, particular emphasis should be placed on parameters germane to IEDs, including morphology, topography, frequency, and activation, by provocative procedures (hyperventilation, photic stimulation, and sleep).