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Seizure Lateralization During EEG Monitoring in Patients with Bilateral Foci: The Cluster Effect
Author(s) -
Haut Sheryl R.,
Legatt Alan D.,
O'Dell Christine,
Moshé Solomon L.,
Shinnar Shlomo
Publication year - 1997
Publication title -
epilepsia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.687
H-Index - 191
eISSN - 1528-1167
pISSN - 0013-9580
DOI - 10.1111/j.1528-1157.1997.tb01260.x
Subject(s) - concordance , epilepsy , electroencephalography , lateralization of brain function , analysis of variance , psychology , medicine , anesthesia , audiology , neuroscience
Summary : Purpose: To determine whether seizures that occur in clusters are more likely to reflect activity of the same focus than are seizures that are widely separated in time. Methods : EEG monitoring data from 14 patients with bilateral independent seizure onsets were analyzed. Twelve of the 14 patients had surface recordings only, and two had implanted electrodes. Interseizure intervals (ISIs) for 151 seizure pairs were measured. Seizure onsets were classified as right hemispheric, left hemispheric, or indeterminate. Seizure pairs were classified as concordant for hemisphere of onset, discordant, or indeterminate. The relation between seizure‐pair concordance and ISI was examined by using univariate analysis and analysis of variance (ANOVA). Results : Both seizures originated from the same hemisphere in 61 (75%) of 81 seizure pairs with ISIs >8 h, compared with 28 (55%) of 51 seizure pairs with ISIs >8 h (p < 0.015). The cluster effect was not more pronounced for ISIs <2 h. ANOVA demonstrated that the relation between IS1 and seizure concordance was not a result of the variability in seizure rates among patients. In three patients, the presence of bilateral foci was not demonstrated until more than five seizures were recorded. Conclusions : Seizures that occur after an IS1 of <8 h are more likely to come from the same side as the previous seizure than are those with longer ISIs. Thus clustered seizures should not be given the same weight as seizures widely separated in time. In addition, more than five seizures may sometimes be needed to adequately assess patients being evaluated for epilepsy surgery.