Are High-Amplitude Background Slow Waves Normal in Young Children?

Sometimes considered a sign of infantile spasm-related hypsarhythmia – or just an indication that patients need to be followed – high-amplitude posterior waves are common in young children.

Columbus, OH — March 2018

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.”


 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. Journal of Clinical Neurophysiology. 2018 Jan 8. [Epub ahead of print]