Late-onset temporal lobe epilepsy: Enlarged amygdala-hippocampus indicates interictal epileptic activity at electroencephalography and memory impairment.

Late-onset temporal lobe epilepsy (TLE) sometimes manifests with enlargement of the amygdala or hippocampus. This study aimed to clarify the yet unknown clinical significance of amygdala-hippocampal enlargement in late-onset TLE. We retrospectively analyzed the late-onset TLE (≥ 60 years old) patients admitted to Kyoto University Hospital between 2000 and 2019. To investigate whether the patient group has enlarged amygdala or hippocampus compared to the healthy control, we performed MRI volumetry with hippocampal subfield segmentation. Furthermore, to evaluate the associations of amygdala or hippocampal enlargement with clinical manifestations, we analyzed the relationship between volume changes and seizure semiology, interictal epileptiform discharges (IED) on electroencephalography, Wechsler Memory Scale-Revised, 18F-fluorodeoxyglucose positron emission tomography (FDG-PET), and neural autoantibodies. We analyzed 33 patients (19 male. Age: mean/median/SD/range = 68.8/69/5.0/61-82. Epilepsy onset: 64.9/64/4.1/60-77 years. Years after epilepsy onset: 3.9/4/2.6/1-14 years). MRI volumetry revealed (1) an increase in the volume of the left amygdala and left hippocampus-amygdala transition area (HATA) and (2) a volume decrease in the bilateral ventral diencephalon, compared to healthy subjects. FDG-PET revealed glucose hypometabolism in the bilateral presubiculum and left hippocampal tail (p < 0.05, Wilcoxon rank-sum test). Memory impairment was more severe in patients with enlarged HATA or left amygdala (left HATA, p = 0.0121; right HATA, p = 0.0039; left amygdala, p = 0.0285; MANOVA). The hippocampal volume ipsilateral to the IED was larger than that contralateral to the IED (p = 0.0053, Wilcoxon rank-sum test). The left hippocampal volume significantly differed depending on IED prevalence (p = 0.0039, ANOVA), where higher IED prevalence was associated with larger hippocampal volume. The present study provides the supporting findings for the association of amygdala-hippocampal enlargement with IED and memory impairment in late-onset TLE, suggesting that amygdala-hippocampal enlargement is a clinically significant indicator of epileptic excitability and memory impairment.