Abstracts

Several reports indicate that interictal epileptiform discharges (IED) may be more likely to occur over the left cerebral hemisphere than over the right. Some authors additionally assume that the left hemisphere is more likely to generate focal seizures from a localized left-sided epileptogenic zone. The objective of our study was to determine the frequency and type of IED on routine and multi-hour EEGs in a tertiary epilepsy center, to estimate the frequency of left versus right-sided IED and to determine interictal spike distribution pattern differences between adult and pediatric epilepsy patients. Discharges that were generalized with a lateralized component were excluded. The current study retrospectively reviewed 31384 EEGs (25935 routine EEGs and 5449 multi-hour EEGs) recorded on 24003 patients during the period from 1993 to 2003. 7704 of these patients were under the age of 18 years All EEGs were read according to a systematic EEG classification system (Lüders et al., 1993) which included detailed localization and lateralization information about all epileptiform abnormalities. Every patient was only considered once by including the first abnormal EEG. Presurgical long-term video-EEG recordings were not included in the study. Regional IED were recorded in 1628 patients (6.78%). Left-sided regional IED were seen in 815 patients (664 sharp waves, 132 spikes, 13 spike and wave complexes and 6 polyspikes), and right-sided in 574 (450 sharp waves, 106 spikes, 9 spike and wave complexes and 9 polyspikes). Left-sided IED accounted for 58.6% of all regional unilateral regional IED. Right and left-sided regional IED were seen in 239 patients (163 sharp waves, 70 spikes, 4 spike and wave complexes and 2 polyspikes).
EEG recordings with regional IED were seen in 1032 (7.6%) pediatric epilepsy patients and 1032 (6.3%) adults. Among the adults left-sided IED were seen in 565 patients, right-sided in 361 and right and left sided in 106, with left-sided regional IED accounting for 61% of all regional unilateral IED. Among pediatric patients left-sided IED were seen in 260 patients, right-sided in 195 and right and left-sided in 136, with left-sided IED accounting for 57% of all regional IED. Regional epileptiform discharges were seen in approximately 7% of patients.
Interictal epileptiform discharges were more frequently seen in the left hemisphere (59% of all unilateral regional epileptiform discharges). Age adjusted analysis of the data revealed that this left-sided predominance was only mildly increased in adults as compared to epilepsy patients under the age of 18 years.