Persistence of Hypsarrhythmia in Children Beyond the Age of Three Years

Occurrence of hypsarrhythmia after the age of 3 years is rare. The objective of this study is to describe a group of patients who have persistence of hypsarrhythmia after the age of 3 years. The authors retrospectively reviewed the EEGs of 24 patients with hypsarrhythmia. Electroencephalographies (EEGs) were scored using a hypsarrhythmia scale. The clinical data of 7 patients with EEG scores greater than 9 at ages >= 3 years were analyzed. The mean age was 5.7 years (range, 3-8.7 years). EEG background amplitudes ranged from 200 to 500 mu V in 5 patients and it was greater than 500 mu V in the other 2. Six patients had electrodecremental responses. The etiology was developmental in 3 patients, mitochondrial disease in 2, and hypoxic ischemic encephalopathy in 2. Our study suggests that a subgroup of patients with hypsarrhythmia may not transition to a Lennox-Gastaut pattern or normalization after the age of 3 years.