A proposal for a new clinical entity: transient epileptic amnesia complex syndrome (TEACS)

Transient epileptic amnesia (TEA) is a special type of temporal lobe epilepsy, the main symptom of which is recurrent amnesia attacks. In the late 1990s, Zeman et al. developed the following diagnostic criteria for TEA: (i) recurrent, witnessed episodes of amnesia; (ii) other cognitive functions remain intact during attacks; and (iii) evidence of epilepsy. It was subsequently reported that patients with TEA almost always demonstrate two other types of memory symptoms: accelerated long-term forgetting (ALF) and autobiographical amnesia (AbA). As a result, it has been recognised that TEA causes at least three characteristic types of amnesia, that is, amnesia attacks, ALF, and AbA. In this report, we present two clinical cases, in which the patients showed symptoms of ALF and/or AbA without suffering any type of epileptic seizure, including amnesia attacks, for a long time. We discuss a syndrome associated with TEA, particularly the relationship between TEA and ALF/AbA, based on our two cases and a review of the literature. In addition, we propose a new clinical entity, which we named 'transient epileptic amnesia complex syndrome (TEACS)' and will help to ensure that physicians recognise the existence of such cases and do not overlook this condition. Furthermore, the following diagnostic criteria for TEACS are proposed. (i) The patient is middle-aged to elderly at onset and has no history of epilepsy. (ii) ALF and/or AbA have been definitively diagnosed. (iii) The ALF and/or AbA precede TEA attacks and/or other epileptic seizures. (iv) Except for the ALF/AbA, the patient's cognitive functions are confirmed to be intact via clinical examinations. (v) There is evidence for a diagnosis of epilepsy. Such evidence can include: (i) wake or sleep electroencephalography; or (ii) a clear response to anti-epileptic drugs. Furthermore, we describe our hypotheses regarding the pathogenesis of ALF/AbA and discuss the relationships between TEACS and other epileptic amnesia-related syndromes.