Interrater reliability of the international consensus definition of drug-resistant epilepsy: a pilot study

We evaluated the interrater reliability of the consensus definition of drug-resistant epilepsy proposed by the International League Against Epilepsy. According to the definition framework, outcome of each antiepileptic drug (AED) trial was categorized as "seizure freedom" or "treatment failure." This level 1 assessment was used to determine the level 2 classification, which defined drug-resistant epilepsy as the failure of adequate trials of two or more AED schedules to achieve sustained seizure freedom. Two raters classified treatment outcomes of 150 patients independently. The patients had received a total of 428 trials of AEDs. Categorization of level 1 outcome to individual AED trials by the raters was consistent in 413 (96.5%). For the level 2 classification of drug-resistant or drug-responsive epilepsy, there was absolute agreement between the raters in 141 patients (94%), with a κ index of 0.91 (P<0.001). The definition appeared to have a high degree of interrater reliability in this setting.