Abstracts

RATIONALE: Although adult EEG studies demonstrate left hemispheric favoring of epileptiform discharges (EDS), little is known about when such asymmetries first become evident. We studied if, where, and when similar EDS favoring occurs in children.
METHODS: Thirteen months of consecutive EEG reports were retrospectively examined from Seattle[ssquote]s Children[ssquote]s Hospital. Electroencephalographers were blind to study objectives. Recorded data included age in months, if it was a first EEG study, general findings, location of EDS (left or right), and interpreting electroencephalographer. Standard age-associated normal findings were not recorded. EDS were defined as interictal spikes, interictal sharp waves, ictal activity or PLEDS. Age-appropriate neonatal sharp waves were not considered epileptiform. Both premature and full gestation infants were considered one month old until they entered their second month of life. Bilateral independent EDS were coded as predominantly left or right; if the encephalographer didn[ssquote]t specify they were tallied as [dsquote]bilateral EDS.[dsquote] Data were entered into a computerized database and statistical analysis performed.
RESULTS: 1327 reports were reviewed. 2 board-certified electroencephalographers and 2 board-eligible, recent Epilepsy fellowship graduates interpreted the EEG[ssquote]s. All used digital montages according to their preference. Mean age was 78 months. Focal EDS were seen in 258 records with right in 159 and left in 99 (p[lt]0.01 chi square). Mean ages of those with EDS showed right 71 months, left 83 months. 727 (55%) results were first EEG (FEEG) studies; in this group, mean ages of those with EDS on the right were 45 months, left 76 months. FEEG results showed the right hemisphere displayed EDS more often in the first 54 months (n=37 right, 21 left), but between 55-78 months EDS occured symetrically (n= 10) and after 79 months left-sided EDS predominated (n=12 right, 19 left). Comparing EDS by side with 2 age-cohorts, [lt]54 and [gt] 54 months, showed this age-related shift to be significant ( p=0.023 fisher[ssquote]s exact). This suggests no reading bias for right-sided EDS. Furthermore, hemispheric favoring of EDS seems age-influenced. This age-associated shift in FEEG records may help explain the discordant left-favoring EDS data from adults and the right-sided findings in this study. Our FEEG findings parallel several normal parameters of childhood development: infantile blood flows show right-sided hemispheric favoring up to 3 years of age and transition to the left therafter, additionally left hemispheric growth lags that of the right in infancy, yet undergoes a marked growth spurt between ages 3-6 that ultimately outpaces the right. These shifts correspond temporally with developing handedness and language. It may be that mechanisms of normal laterlizations such as handedness and language similarly influence abnormal EDS-prone regions . Clarifying these influences in other cohorts may suggest age-associated factors that alter susceptabilities to focal EDS.
CONCLUSIONS: Focal EDS in our pediatric cohort appear more commonly over the right hemisphere. In first EEG evaluations, this finding is age-dependent: in infancy EDS favor the right side, at 54 months they occur symmetrically, and after 79 months they favor the left side.