High amplitude background slow waves in normal children aged 3 to 18 months: Implications for the consideration of hypsarhythmia

Purpose: To assess for the presence of high amplitude EEG background slow waves in normal young children. Methods: One hundred children with normal development ages 3 to 18 months had normal EEGs for spells and did not have seizures or epilepsy. Three electroencephalographers retrospectively reviewed 5 minutes of stable stage II sleep to measure background slow waves for peak-to-peak amplitudes. A standard 10-20 longitudinal bipolar montage was used. Interrater agreement was assessed by intraclass correlation coefficient. Results: Interrater agreement between reviewers in the assessment of recurrent slow wave amplitudes was excellent (intraclass correlation coefficient ¼ 0.97). Slow wave amplitudes were the highest in the posterior head regions for all patients. We found recurring slow waves of,200 mV, 200 to 299 mV, 300 to 399 mV, 400 to 499 mV, and .500 mV in 17%, 49%, 30%, 3% and 1%, respectively. Conclusions: Although hypsarhythmia typically includes high amplitude background slow waves of .200 or .300 mV, we found that 83% and 34% of normal children had recurring posterior background slow waves of .200 or .300 mV, respectively. These data may be useful in the EEG background assessment of young children, for determining the presence or absence of hypsarhythmia, and determining treatment response in children with epileptic spasms.