Abstracts

Rationale: Hypsarrhythmia is an EEG pattern characterized by high amplitude, chaotic, disorganized background with multifocal spikes occurring usually during the first year of life. Late persistence of infantile spasms without hypsarrhythmia has been described but 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 Methods: The EEG database of our institution was searched to identify EEG recordings with high amplitude, chaotic background, multifocal spikes or hypsarrhythmia. Only patients with at least 2 EEGs were included in the study. EEGs were reviewed blinded to the clinical information and scored using a hypsarrhythmia scoring scale (Kramer, et al 1997). Items scored included disorganization, delta activity, amplitude, spikes and other abnormalities with scores from 0 to 3 each. Single item scores were added for a total score in each EEG recording. The clinical data of patients with EEGs with total scores greater than 9 (usually unequivocal hypsarrhythmia) at ages older than 3 years were analyzed. Results: There were 24 patients with hypsarrhythmia who had a total of 99 EEGs. Six of them had EEGs with hypsarrhythmia at age 3 years or older with total hypsarrhythmia scores of 9 to 13. The mean age was 5.4 ±2.2 (range: 3.1-8.7 years). All 6 patients had chaotic EEGs with no synchrony, and no anterior to posterior gradient. Five patients had EEG background amplitudes from 200-500 μV and one patient greater than 500 μV. Five patients had electrodecremental response. There were 2 patients with lissencephaly, 2 with mitochondrial disease and 2 cryptogenic. Conclusions: Twenty five percent of our population with hypsarrhythmia had persistence of this pattern after the age of 3 years. Our study suggests that a subgroup of patients may not transition to a Lennox-Gastaut pattern or normalization. Treatment response to antiepileptic drugs in this group of patients may be different compared to younger ages. Follow-up EEG’s in patients with history of hypsarrhythmia may be warranted as seizures may not be prominent.