TRANSIENT EPILEPTIC AMNESIA - A DESCRIPTION OF THE CLINICAL AND NEUROPSYCHOLOGICAL FEATURES IN 10 CASES AND A REVIEW OF THE LITERATURE

Objectives-To clarify the clinical and neuropsychological aspects of t ransient epileptic amnesia (TEA) based on 10 personally studied cases as well as review of 21 previously published cases; and to propose ten tative diagnostic criteria for the diagnosis of TEA. Methods-All 10 pa tients and informants underwent a standardised clinical interview. The radiological and neurophysiological (EEG) data were also reviewed in all cases. The diagnosis of transient epileptic amnesia was made on th e basis of the following criteria: (1) there was a history of recurren t witnessed episodes of transient amnesia; (2) cognitive functions oth er than memory were judged to be intact during typical episodes by a r eliable witness; (3) there was evidence for a diagnosis of epilepsy. T his evidence was provided by either (a) wake or sleep EEG, or (b) the co-occurrence of other seizure types (if their roughly concurrent onse t or close association with episodes of transient amnesia suggested a connection), or (c) a clear cut response to anticonvulsant therapy, or by a combination of these three factors. In addition all patients wer e administered a comprehensive neuropsychological test battery designe d to assess verbal and non-verbal anterograde memory and retrograde me mory for famous personalities and personal events. Their results were compared with those of 25 age and IQ matched normal controls. Results- TEA usually begins in later Life, with a mean age of 65 years in this series. Episodes are typically brief, lasting less than one hour, and recurrent, with a mean frequency of three a year. Attacks on waking ar e characteristic. Repetitive questioning occurs commonly during attack s. The anterograde amnesia during episodes is, however, often incomple te so that patients may later be able to ((remember not being able to remember''. The extent of the retrograde amnesia during attacks varies from days to years. Most patients experience other seizure types comp atible with an origin in the temporal:lobes, but transient amnesia is the only manifestation of epilepsy in about one third of patients. Epi leptiform abnormalities arising from the temporal lobes are most often detected on interictal sleep EEG. Despite normal performance on tests of anterograde memory, many patients complain of persistent intericta l disturbance of autobiographical memory, involving a significant but variable loss of recall for salient personal episodes. The epochs affe cted may predate the onset of epilepsy by many years. Conclusions-TEA is an identifiable syndrome and comprises episodic transient amnesia w ith an epileptic basis, without impairment of other aspects of cogniti ve function. Future studies should consider the question of whether TE A reflects ictal activity or a postictal state, and the mechanism of t he persistent autobiographical amnesia. It is hypothesised that the la tter may result in part from impairment of very long term memory conso lidation as a result of epileptic activity in mesial temporal structur es.