Abstracts

Left hemispheric predominance of interictal epileptiform discharges (IEDs) has been highlighted by a previous study from our center. Lateralization becomes slightly more prominent in adults than in children. However, no data on lateralization of benign focal epileptiform discharges of childhood (BFED) are available. The objective of our study was to determine the distribution, frequency and type of epileptiform abnormalities as a function of age and to compare it with BFEDs and slowing. The current study retrospectively reviewed all routine (25,935) and multi-hour (5449) EEGs during a consecutive 10 year period. 7704 patients under the age of 18 years were included. All EEGs were read according to a systematic EEG classification system (Lüders et al., 1993). EEGs were reviewed for unilateral epileptiform discharges, unilateral BFED and slowing. The lateralization of the abnormality was counted only once for each patient by including just the first abnormal EEG. Additionally subsequent EEGs of all infants under the age of 3 years with unilateral IED were reviewed for change in lateralization of IED over time. EEG recordings with unilateral regional IED were seen in 612 (8%) pediatric patients; left-sided IED were seen in 260 patients (55%), right-sided in 213 (45%) and both right and left-sided in 139. There was no difference between infants (40 left, 33 right) and older children (220 left, 180 right).
BFEDs were seen in 136 (49 left, 50 right, 37 bilateral) out of 7704 pediatric patients (1.8%). No BFEDs were seen under 3 years of age. Continuous unilateral regional slow was seen in 193 patients, with 97 (20 infants) on the left and 96 (18 infants) on the right. Intermittent slow (less than 80% of the recording) was seen in 199 patients (32 infants) on the left (61.6%) and in 123 patients (9 infants) on the right.
In 118 infants with unilateral or bilateral regional IED, the lateralization of IED in subsequent EEGs was reviewed. 32 patients with uni- or bilateral IEDs had subsequent EEGs, with localization changed in 9. Two patients converted from left to right (one of these two underwent epilepsy surgery on the left), and none converted from right to left. Five patients with initially left sided and two with initially right sided IED showed bilateral IEDs subsequently. Two patients with initially bilateral AEDs had subsequently right-sided IED in one and left-sided IED in the other. Regional epileptiform discharges were seen in approximately 8% of patients. Interictal epileptiform discharges and intermittent slow were more frequently seen in the left hemisphere. Age adjusted analysis of the data showed no difference between infants and older children. Continuous slow and BFEDs were equally distributed between both hemispheres. Longitudinal follow up of consecutive infant EEGs did not reveal a trend towards IED conversion from one side to the other.