Age at focal epilepsy onset varies by sex and hemispheric lateralization

Background: Previous studies have shown that interictal epileptiform discharges favor the left hemisphere in adults but the right side in children up until age 5. This may be due to sex-influenced asymmetric brain maturation. To clarify this relationship, the authors analyzed age at epilepsy onset by sex and by lateralization of epileptiform activity. Methods: An adult epilepsy center long-term monitoring database was used to define patients with exclusively unilateral epileptiform findings. Three groups were studied: any epileptiform activity (n = 404), ictal activity (n = 287), and interictal activity (n = 265). The second and third groups were drawn from the first group and the second and third groups overlapped with each other. Side of lateralized finding and sex were analyzed via factorial two-way analysis of variance with the outcome variable being age at epilepsy onset. Comparison analysis included patients with generalized epilepsy (n = 114), nonepileptic seizures (NES, n = 232), and surgical mesial temporal sclerosis (MTS, n = 116). Results: Patients with unilateral epileptiform activity displayed bimodal epilepsy onset ages with infant and adolescent peaks. For patients with a right-sided focus, epilepsy onset was earlier in men (14.4 years) than women (20.7 years). In contrast, among patients with a left-sided focus, epilepsy began earlier in women (18.2 years) than men (19.9 years, p < 0.01). Parallel results were found in unilateral ictal (p < 0.01) and unilateral interictal activity (p = 0.01). Patients with surgical MTS, NES, or generalized seizure showed no similar patterns. Conclusions: In adult patients with focal epilepsy, sex and lateralized epileptiform abnormalities may be related to age at epilepsy onset.