CHICAGO — Analysis of EEG patterns in a group of drug-naive children diagnosed with absence seizures found that although 80% of individuals demonstrated consistent patterns, only 18% of this group demonstrated the classic pattern commonly described in textbooks, according to Dr. Yoshimi Sogawa.
“Textbooks will tell you that absence bursts are characterized by 3-Hz spike and wave discharges, are nonevolving, and start and end abruptly. What we are finding is that is not true,” said Dr. Sogawa, a neurologist at the Children's Hospital at Montefiore, New York.
The study participants, part of the largest cohort gathered to date of children with absence seizures (n = 400), were enrolled in the National Institutes of Health Childhood Absence Epilepsy Trial. Dr. Sogawa analyzed the EEGs of 103 drug-naive children. Of this group, 80 children showed a consistent EEG pattern while 23 who showed intraindividual variability were excluded from further analysis. Making an analogy to a musical sonata, Dr. Sogawa subdivided the 3-Hz spike-wave discharges into multiple components.
Within a burst, she identified five components:
▸ Introduction (I): initial change from baseline, consisting of irregular slowing with or without spikes.
▸ Exposition (E): the characteristic 3-Hz spike-wave discharge.
▸ Development (D): variations on the 3-Hz pattern.
▸ Recapitulation (R): reemergence of the E-like pattern.
▸ Coda (C): combination of rhythmic slow activity.
With these elements, Dr. Sogawa found that three predominant patterns emerge. The most frequent combination was the I-E-D-C pattern (59%), followed by the semiclassic I-E-D-R pattern (23.8%), and then the “classic” I-E-C pattern (17%).
“These patterns bring up the question: What is childhood absence epilepsy? It is not a single entity. There are so many variations,” according to Dr. Sogawa. This variability certainly brings into question the diagnostic value of the classic EEG pattern.
Dr. Sogawa suggested that the distribution of a particular EEG component may reflect genetic variability, perhaps related to calcium channel function, and may underlie the differences in sensitivity to antiepileptic medications that she often sees. Speaking at the annual meeting of the American Academy of Neurology, Dr. Sogawa said genetic analyses are underway to see how different EEG patterns correlate with drug response and comorbidity.
Dr. Sogawa said she had nothing to disclose.