Late-onset idiopathic (genetic) generalized epilepsies: Clinical and EEG findings

We investigated the occurrence and clinical characteristics of late-onset idiopathic generalized epilepsies (IGEs). We also provided a statistically meaningful definition for late-onset IGE in this large cohort of patients.

In this cross-sectional retrospective chart review study, all patients with a clinical diagnosis of IGE were recruited at the outpatient epilepsy clinic at Shiraz University of Medical Sciences from 2008 until 2019. We defined "late-onset IGE" according to the following equation: those with an age at onset of their seizures above X years [X = mean age at the seizure onset of all patients + 2 × (standard deviation)].

During the study period, 601 patients with IGE were registered at our epilepsy clinic. Late-onset IGE was defined as having an age at onset of above 26 years. Fifteen patients (2.5%) had late-onset IGE. The syndromic diagnosis of these patients included: IGE with absences [6 patients (40%)], generalized tonic-clonic only (GTC-only) [5 patients (33.3%)], and juvenile myoclonic epilepsy (JME) [4 patients (26.7%)].

While late-onset IGE (IGE with an age at onset of above 26 years) is not common, one should consider the possibility of its occurrence in adults with new-onset seizures. This condition shares many of the clinical and electroencephalograic features of classical IGEs, which supports the hypothesis that IGE syndromes in different age groups share common biological determinants.