Asymmetry of generalized discharges in idiopathic generalized epilepsy in adults

Generalized epileptiform discharges (GEDs) in idiopathic generalized epilepsy (IGE) are classically considered symmetrical in amplitude, although this has not been formally tested. This is a major knowledge gap, since asymmetry is conventionally considered an atypical feature, with clinical implications. Furthermore, if such asymmetry exists, it would challenge the concept that IGE engages homogenously the entire brain and rather supports the hypothesis that IGE is shaped by delimited networks. Here, we asked whether GEDs in IGE are asymmetrical and whether this asymmetry exhibits individual specificity. Across 62 patients with IGE recorded with scalp electroencephalography (EEG), we found that GEDs exhibit hemispheric asymmetry (mean, 95% confidence interval [CI]: 22%, 17%-28%) in comparison to control conditions and preceding baseline. Importantly, this asymmetry is systematic across several repetitions of GEDs. Furthermore, the asymmetry varies more across than within patients, indicating that it operates as an individual trait. In contrast, there was no left-right hemispheric preference, and the asymmetry was not different when comparing wake- and sleep-recorded GEDs. Beyond the clinical relevance of providing a formal range for GEDs asymmetry in IGE (upper range of 95% CI ~30% asymmetry), this work supports the concept of IGE as being shaped by distinct and lateralized cortical brain networks.