Estimating the importance of epileptiform abnormalities discovered on cassette electroencephalographic monitoring

Assessment of hairline EEG as a screening tool for nonconvulsive status epilepticus

PURPOSE

Because of the high incidence of nonconvulsive status epilepticus (NCSE), the attraction of a "quick and easy" screening electroencephalogram (EEG) is obvious. Previous studies have shown utility of hairline EEG in diagnosing epilepsy. However, this technique has not been evaluated as a screening tool for NCSE. We wanted to provide proof of principle that a screening hairline EEG has sufficient sensitivity to use as a screening tool for diagnosing NCSE.

METHODS

A total of 120, 2- to 3-min EEG samples of normal and various abnormal digital EEG studies were reformatted in three six-channel montages (A, longitudinal bipolar; B, referential to ipsilateral ear; C, referential to contralateral ear) that mimicked a hairline recording and were interpreted by five neurophysiologists. The test data interpretation was compared with the original EEG interpretation.

RESULTS

Performance was best with montages A and B; 71% and 70.5% of the samples were interpreted correctly by using these montages. Only 65% of the samples were correctly interpreted by using montage C. With the best montage (A), the sensitivities ranged from 91% for normal EEG to 54% for periodic lateralized epileptiform discharges (PLEDs). The sensitivity for seizures was only 72%. Seizures were frequently misinterpreted as more benign patterns such as normal and diffuse slowing.

CONCLUSIONS

EEG data reformatted to resemble a hairline EEG had low sensitivity for detecting seizures. As a result, we do not recommend further pursuit of hairline EEG as a "quick and easy" screening tool for NCSE.

Incidence of spikes and paroxysmal rhythmic events in overnight ambulatory computer-assisted EEGs of normal subjects: a multicenter study

The incidences of spikes and paroxysmal rhythmic events (PREs) in 10-h overnight EEGs of normal adult volunteers (n=135) were studied at 11 sites with a computer-assisted ambulatory EEG monitoring system with automatic spike and PRE detection. Spikes were evident in the overnight EEG of 1 subject (0.7%), and PREs were apparent in the overnight EEG of the same subject (0.7%). The incidences of spikes of 24 other subjects with a history of migraine and/or a family history of epilepsy were 12.5 and 13.3%, respectively. The overnight EEGs of these subjects were significantly more likely to show spikes than the overnight EEGs of subjects without migraine or a family history of epilepsy.

The value of EEG in children with chronic headaches

To establish the usefulness of electroencephalography (EEG) as a diagnostic tool in the evaluation of headaches in children, we retrospectively reviewed the records of all children referred to our outpatient neuropediatric clinic because of recurrent headaches. Of 312 children, 257 (82%) underwent EEG tracings: 143 of the children who had had EEG recordings were diagnosed as migraineurs. In 31 (12%) of the children, the EEG revealed epileptic activity. The highest incidence of epileptic EEG activity was found amongst the children with very brief headaches. In 22 (8.6%) of the children, diffuse or focal slowing was detected. The group with migraine headache had a significantly higher incidence of slowing than the group with other types of headaches. There was no correlation between focal EEG abnormalities and brain radioimaging studies or clinical course. We conclude that despite the high incidence of epileptic abnormalities, the contribution of EEG to diagnosis and treatment in children with chronic headache is minimal, and should not be routinely prescribed in these children.

Aspartame has no effect on seizures or epileptiform discharges in epileptic children

The effects of aspartame (L-aspartyl-L-phenylalanine methyl ester; APM) on the neurological status of children with well-documented seizures were examined in a randomized, double-blind, placebo-controlled, crossover study. We report on 10 children (5 boys, 5 girls, ages 5-13 yr) who were tested for 2 weeks each on APM and placebo (single morning dose, 34 mg/kg). Seven children had generalized convulsions with 4 also having absence episodes. One child had absence seizures and 2 had complex partial seizures only. On each arm of the study, children were admitted to the hospital for a standard 21-lead electroencephalogram (EEG), continuous 24-hour cassette EEG, and determination of biochemical variables in plasma and urine. Subjects completed the Subjects Treatment Emergent Symptoms Scale (STESS) and parents the Conners Behavior Rating Scale. There were no significant differences between APM and placebo in the standard EEG or 24-hour EEG. No differences were noted for the STESS or the Conners ratings, and no differences were noted for any of the biochemical measures (except for expected increases in phenylalanine and tyrosine after APM). Our findings indicate that, in this group of vulnerable children, APM does not provoke seizures.

A review of interictal cerebral blood flow in the evaluation of patients for epilepsy surgery

The literature on cerebral blood flow (CBF) studies in patients with epilepsy is critically reviewed. Two methods are specifically addressed, radioactive xenon delivered through inhalation or vascularly, and single photon emission computed tomography (SPECT) using various tracers. Both regional and global blood flow were used in these studies to assess focal and generalized seizures. Electroencephalogram (EEG) foci were determined by various techniques, including interictal and ictal recordings from scalp or intracranial electrodes. All studies reported a positive concordance between EEG foci and CBF. However, there was a high incidence of false positive and false negative results. The methodology of almost all of the studies was inadequate to assess accurately the sensitivity and specificity of CBF to localize the seizure focus. Even when conservative estimates were made, the sensitivity and specificity of CBF was too low to be used as a diagnostic test for epilepsy, and inadequate to localize the EEG focus in the evaluation of patients for epilepsy surgery.

The utility of ambulatory EEG monitoring in typical absence seizures

In this study 8 hours ambulatory EEG monitoring (A/EEG) was performed in 25 outpatients with electroclinical evidence of absence attacks, in order to evaluate the possibility of objective quantification of the epileptic discharges, their distribution during the daytime and their relationship with evident behavioral correlates. A comparison between data obtained by A/EEG and standard EEG (S/EEG) was also made. The results have shown that: 1) it was possible to perform real quantification of the epileptic discharges only through the A/EEG test; 2) the two peaks of a greater incidence of the epileptic discharges corresponded to the execution of relaxing activities and ones requiring a low level of attentiveness; 3) a large number of epileptic generalized discharges did not exhibit a signal pattern like that of a "seizure", although they were of long duration; and 4) in six patients who showed the normalization of S/EEG and the disappearance of the absences after one month of valproate therapy, A/EEG revealed the persistence of epileptic discharges. These data demonstrate that A/EEG is a very useful technique for the quantification of paroxysmal discharges and that it may be of importance in the management of this kind of epileptic disorder.