Do neurologists agree in diagnosing drug resistance in adults with focal epilepsy?

OBJECTIVE: To evaluate interrater agreement in categorizing treatment outcomes and drug responsiveness status according to the International League Against Epilepsy (ILAE) definition of drug‐resistant epilepsy. METHODS: A total of 1053 adults with focal epilepsy considered by the investigators to meet ILAE criteria for drug resistance were enrolled consecutively at 43 centers and followed up prospectively for 18‐34 months. Treatment outcomes for all antiepileptic drugs (AEDs) used up to enrollment (retrospective assessment), and on an AED newly introduced at enrollment, were categorized by individual investigators and by 2 rotating members of a 16‐member expert panel (EP) that reviewed the patient records independently. Interrater agreement was tested by Cohen’s kappa (k) statistics and rated according to Landis and Koch’s criteria. RESULTS: Agreement between EP members in categorizing outcomes on the newly introduced AED was almost perfect (90.1%, k = 0.84, 95% confidence interval [CI] 0.80‐0.87), whereas agreement between the EP and individual investigators was moderate (70.4%, k = 0.57, 95% CI 0.53‐0.61). Similarly, categorization of outcomes on previously used AEDs was almost perfect between EP members (91.7%, k = 0.83, 95% CI 0.81‐0.84) and moderate between the EP and investigators (68.2%, k = 0.50, 95% CI 0.48‐0.52). Disagreement was related predominantly to outcomes considered to be treatment failures by the investigators but categorized as undetermined by the EP. Overall, 19% of patients classified as having drug‐resistant epilepsy by the investigators were considered by the EP to have “undefined responsiveness.” SIGNIFICANCE: Interrater agreement in categorizing treatment outcomes according to ILAE criteria ranges from moderate to almost perfect. Nearly 1 in 5 patients considered by enrolling neurologists to be “drug‐resistant” were classified by the EP as having “undefined responsiveness.”