Pure amnestic seizure: A clinico-intracranial EEG study.

OBJECTIVE: Enduring anterograde amnesia is caused by lesions in bilateral mesial temporal lobes. However, whether transient dysfunction of bilateral mesial temporal regions induces reversible amnesia has not been proven. We investigated this association in patients with epilepsy and analyzed the electroclinical correlation during pure amnestic seizures (PAS). PAS are defined as seizures with anterograde amnesia as the only ictal manifestation, accompanied by preserved responsiveness and other cognitive functions.

METHODS: We retrospectively searched our intracranial EEG database to find PAS. Pure ictal amnesia was confirmed by immediate and comprehensive ictal examinations.

RESULTS: Among 401 patients who underwent intracranial EEG recording, three patients with temporal lobe epilepsy (TLE) manifesting PAS were identified. The patients talked and behaved normally during seizure but did not remember the episodes afterwards. Ictal discharges were confined to bilateral mesial temporal regions, with no or mild involvement of surrounding structures. Spread of low-voltage fast activities to bilateral mesial temporal regions corresponded to onset of ictal anterograde amnesia. Two patients underwent unilateral mesial temporal resection and became seizure-free with improvement in cognitive functions.

SIGNIFICANCE: PAS is a rare ictal semiology in TLE. Bilateral mesial temporal regions that play a critical role in memory encoding are presumably the symptomatogenic zones for PAS.