Transient epileptic amnesia has been considered a syndrome of mesial temporal lobe epilepsy characterized by (1) recurrent episodes of isolated memory impairment of epileptic cause (ictal or postictal) while other cognitive functions remain intact; (2) interictal memory disturbances of accelerated long-term forgetting and autobiographical and topographical amnesia; and (3) late age of onset with a mean of 57 years. The duration of episodes of amnesia is usually less than an hour with usual recurrence of around 20 times each year in untreated patients. In addition, brief seizures typical of mesial temporal lobe epilepsy are detected in two thirds of patients. Interictal EEG, particularly when recorded in sleep, shows temporal lobe spikes whereas EEG during attacks of amnesia demonstrates either ictal discharges or postictal features. In most cases of transient epileptic amnesia, no clear cause for the epilepsy is identified though MRI may show hippocampal atrophy or focal structural lesions in the temporal lobes. Transient epileptic amnesia is considered rare though it is frequently underdiagnosed or misdiagnosed as transient global or psychogenic amnesia. Patients with transient epileptic amnesia usually have an excellent prognosis; seizures respond extremely well to monotherapy with small doses of lamotrigine or levetiracetam though interictal memory disturbances may persist.
In this article, Dr. C P Panayiotopoulos of St. Thomas’ Hospital discusses the clinical manifestations, biological basis, and diagnosis of transient epileptic amnesia.
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