Polyspike and Waves Do Not Predict Generalized Tonic-Clonic Seizures in Childhood Absence Epilepsy

About 40% of children with childhood absence epilepsy develop generalized tonic-clonic seizures. It is commonly held that polyspike wave pattern on the electroencephalogram (EEG) can predict this development of generalized tonic-clonic seizures. However, there is no firm evidence in support of this proposition. To test this assumption, we used survival analysis and compared the incidence of generalized tonic-clonic seizures in 115 patients with childhood absence epilepsy having either isolated 3-Hz spike wave or coexisting 3 Hz and polyspike waves and other variables. There was no evidence that polyspike waves predicted development of generalized tonic-clonic seizures in patients with childhood absence epilepsy. Later age of onset (>= 8 years) and family histories of generalized tonic-clonic seizures were the only independent predictors. These results have implications for counseling and in the choice of first-line antiepileptic drugs used for childhood absence epilepsy, especially if valproate is chosen based on the observation of polyspike waves.