Mytinger JR, Weber A, Vidaurre J. High Amplitude Background Slow Waves in Normal Children Aged 3 to 18 Months: Implications for the Consideration of Hypsarhythmia. J Clin Neurophysiol. 2018 Mar;35(2):151-154.
To assess for the presence of high amplitude EEG background slow waves in normal young children.
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.
Interrater agreement between reviewers in the assessment of recurrent slow wave amplitudes was excellent (intraclass correlation coefficient = 0.97). Slow wave amplitudes were the highest in the posterior head regions for all patients. We found recurring slow waves of <200 µV, 200 to 299 µV, 300 to 399 µV, 400 to 499 µV, and >500 µV in 17%, 49%, 30%, 3% and 1%, respectively.
Although hypsarhythmia typically includes high amplitude background slow waves of >200 or >300 µV, we found that 83% and 34% of normal children had recurring posterior background slow waves of >200 or >300 µV, 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.
Infantile spasms often co-occur with hypsarhythmia, and high-amplitude slow waves are considered a hallmark of that hypsarhythmia. But pediatric epileptologists at Nationwide Children’s Hospital regularly see electroencephalograms (EEGs) of young children with high-amplitude slow waves who have not experienced infantile spasms.
Should those children be followed? If they have high-amplitude waves, are they at risk for development of epileptic encephalopathy?
In what appears to be the first study of its kind, physician-researchers at Nationwide Children’s reviewed EEGs of 100 normal children, ages 3 months to 18 months, and found that the large majority of them showed recurring posterior slow waves of 200 µV or greater. In fact, more than 30 percent of children had waves of 300 µV or greater.
As long as those kinds of waves stay in the brain’s posterior regions, and in the absence of other signs of hypsarhythmia like EEG epochs of severe disorganization and multifocal spikes, the waves appear to be normal, says John Mytinger, MD, director of Infantile Spasms program at Nationwide Children’s and lead author of the study.
“Other authors have described these high amplitude slow waves in the back of head, but we didn’t know how common they were,” says Dr. Mytinger, who is also an assistant professor of Clinical Pediatrics and Neurology at The Ohio State University College of Medicine. “We don’t want to confuse kids who have those waves with ones who may go on to develop an epileptic encephalopathy.”
The study also has an important implication for children who have experienced infantile spasms, says Dr. Mytinger. Effective treatment in those children can result in electrographic improvement, but epileptologists still regularly see high-amplitude posterior slow waves. These findings show that the waves, by themselves, are not reasons for concern.
“Ultimately, this study demonstrates that when we conduct EEGs on young children who have not experienced infantile spasms, serial EEGs or frequent clinical evaluation may not be necessary given that high-amplitude posterior slow waves are normal,” says Dr. Mytinger. “While we still need to follow children who have experienced infantile spasms, the isolated finding of these waves on a post-treatment EEG is likely normal and additional treatment is not indicated.”