Idiopathic generalized epilepsy: biases and inconsistencies.

OBJECTIVES: Distinguishing Idiopathic Generalized Epilepsy (IGE) from focal epilepsy (FE) can be challenging when IGE cases present with asymmetric clinical or electroencephalographic (i.e., atypical) features. We aimed to identify factors that lead to discordance in IGE diagnoses among epileptologists. METHODS: 41 patients with IGE and 6 patients with FE or mixed focal and generalized epilepsy followed at the NYU Comprehensive Epilepsy Center for ≥5 years were identified. IGE cases included typical (n = 18) and atypical (n = 23) presentations. Anonymized summaries of patients at initial presentation and 5-year follow-up were presented in random order to epileptologists who categorized them as generalized epilepsy (GE), FE, or other. Factors leading to discordance were identified. RESULTS: Inter-rater agreement was moderate for atypical IGE cases at initial presentation (AC1 = 0.54, 95% CI 0.31-0.77, p < 0.01) and 5-year follow-up (AC1 = 0.48, 95% CI 0.25-0.72, p < 0.01). For atypical cases, asymmetric epileptiform activity was most commonly associated with increased discordance. DISCUSSION: Epileptologists may underdiagnose IGE when patients have asymmetric EEG or clinical features. Review of one time point (i.e., vignettes) may mask the diversity of features that may support a localized epilepsy when serial reviews reveal a generalized epilepsy.