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 (> or =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.