Transient epileptic amnesia
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Transient epileptic amnesia (TEA) is a form of temporal lobe epilepsy in which the main if only manifestation of the seizure is a period of amnesia usually lasting around half an hour. During this time period, there may be difficulty in recalling recent events or in laying down a memory for current ones.
Two additional, persistent, interictal memory complaints are common among patients with TEA:
- 'Accelerated Forgetting' is the excessively rapid decay of memories that appear to have been acquired successfully, noted by the patient days to weeks after initial encoding.
- 'Autobiographical Amnesia' is a patchy, but dense, loss of the ability to evoke memories for salient life events, often extending back over several decades, well before the onset of symptoms of epilepsy.
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[edit] Diagnosis
The following diagnostic criteria for the disorder were adopted by a large recent study (Butler et al., 2007):
- A history of recurrent witnessed episodes of transient amnesia.
- Cognitive functions other than memory judged to be intact during typical episodes by a reliable witness.
- Evidence for a diagnosis of epilepsy based on one or more of the following:
1) Epileptiform abnormalities on electroencephalography (EEG).
2) The concurrent onset of other clinical features of epilepsy (e.g., lip-smacking, olfactory hallucinations).
3) A clear-cut response to anticonvulsant therapy.
TEA characteristically starts in middle-age. Attacks are frequent (several/year), brief (usually < 1 hour duration), and often occur on waking. The amnesia involves a variable mixture of anterograde amnesia (inability to form new memories) and retrograde amnesia (inability to retrieve old memories) but the former is often partial so that subjects 'remember not being able to remember'. The frequency and brevity of attacks of TEA distinguish this condition from transient global amnesia (TGA; a syndrome which causes transient amnesia lasting for around 4-6 hours, usually occurring just once, in middle aged people). The diagnosis is often delayed, but the attacks respond promptly to modest doses of anticonvulsant. Some patients' attacks are exclusively amnesic. Others display more familiar features of epilepsy in some or all attacks, typically brief periods of impaired awareness, automatisms or olfactory hallucinations.
[edit] Description of a Transient Epileptic Attack (TEA)
Before: An individual may be made aware that an attack is about to begin by a feeling of discomfort in the stomach or by the detection of a strange smell or a taste in the mouth. Others, however, will have no warning before the onset of memory loss. Very commonly, the attacks occur upon waking from sleep.
During: During an attack, the person is usually unable to remember things that have happened over the past days or weeks. Sometimes, the memory loss may affect events from much further back in the past. In addition, the individual often finds it difficult to retain new information and may ask the same question, such as “What day is it?” or “What are we supposed to be doing today?” repetitively. There is, however, no loss of personal identity and close friends or relatives are usually still recognised. The physical appearance of the person is normally unchanged. Observers may, however, notice some pallor of the skin, a brief ‘loss of contact’ or some automatic movements such as swallowing, lip smacking or fidgeting of the hands. Otherwise, the person responds appropriately to conversation and can continue with activities such as getting dressed, walking or even playing a game of golf. The attack usually lasts less than an hour and the lost memories from the past gradually return. Much longer attacks have however been reported, sometimes continuing for several days.
After: As the amnesia resolves, the memories for the past gradually come back. The person may have no recollection at all of events that occurred during the episode but is often able to “remember not being able to remember”. They may come round surprised to find themselves in a different situation, such as at the doctor’s or lying on the sofa.
This unusual experience can be very frightening both for the person concerned and for friends or family who witness it. The first time it occurs they may put it down to “stress” or “a bad night’s sleep”. However, TEA attacks recur. In some people, they are very infrequent (less than one per year) whereas others experience them as often as once a week. The episodes are usually very similar to each other.
In between attacks, the person is often able to function quite normally. They may, however, notice certain ongoing difficulties with memory.
[edit] Accelerated long-term forgetting (ALF)
Patients with TEA often have difficulty in recalling both verbal and visual information over days to weeks, even if this information was well learned initially.
Accelerated long-term forgetting (ALF) may be described as the abnormally rapid loss of recently learned material from memory.
ALF is often accompanied by a loss of remote memory - the ability to remember things that happened years ago.
Even though accelerated memory loss is a relatively common problem amongst TEA patients, it is undetected by standard tests of memory. Typically these tests examine the ability to store information for up to 30 minutes but the problem of accelerated long-term forgetting in TEA patients is not generally noticeable at this point. It becomes apparent over the following days and weeks.
There are 4 possible reasons why TEA patients experience accelerated forgetting:
1. Seizure activity Seizures in TEA patients commonly occur upon waking suggesting a link between TEA and sleep. It is possible that abnormal electrical activity during sleep disrupts the process of memory consolidation which normally occurs when we sleep.
2. Brain pathology Damage to particular structures in the temporal lobe may both cause attacks of TEA and interfere with the handling of memories.
3. Anticonvulsant medication Antiepileptic drugs sometimes affect memory. However, this is unlikely to be the cause of ALF in TEA, as patients tend to report memory problems before they start taking the antiepileptic drugs and can experience improvement in their memory after taking them.
4. Psychological mechanisms Research has reported that low mood and poor self-esteem are associated with memory problems. These are important factors when investigating patients with epilepsy in general. However, in TEA they do not appear to play an important role in accelerated forgetting.
[edit] Autobiographical Amnesia
People with TEA often notice a patchy but persistent loss of memories of events from their past lives. This difficulty in retrieving memories of significant events, such as weddings and holidays, is a form of ‘autobiographical amnesia’. In addition, some patients with TEA report topographical amnesia for familiar landmarks and routes. This deficit has not so far been characterised further.
Recent work has shown that autobiographical memory is affected for up to 40 years. This memory loss can occur in people whose ability to acquire new memories is intact.
Autobiographical amnesia maybe caused by repeated seizures in the temporal lobe resulting in the progressive “erasure” of memories. Alternatively, autobiographical memory loss may result from subtle changes in the temporal lobe which gives rise to temporal lobe epilepsy and to memory problems. As with ALF , it is unlikely that antiepileptic drugs or problems with mood cause autobiographical memory loss in people with TEA.
[edit] Links
[edit] Literature
- Butler, C.R., Graham, K.S., Hodges, J.R., Kapur, N., Wardlaw, J.M., & Zeman, A.Z.J. (2007) "The syndrome of Transient Epileptic Amnesia." Ann Neurol, 61, 587-598.
- Engmann, Birk; Reuter, Mike: A case history of sudden memory dysfunction – caused by transient epileptic amnesia. Akt Neurol 2003; 30: 350-353
- Manes, F., Hodges, J.R., Graham, K.S., et al. (2005). "Focal autobiographical amnesia in association with transient epileptic amnesia." Brain, 124, 499-509.
- Mendes, Marcelo Heitor: Transient epileptic amnesia: an under-diagnosed phenomenon? Three more cases. Seizure. 2002 Jun; 11(4): 238-242
- Rabinowicz, Adrián L.; Starkstein, Sergio E.; Leiguarda, Ramón C.; Coleman, Anton E: Transient epileptic amnesia in dementia: a treatable unrecognised cause of episodic amnestic wandering. Alzheimer Dis Assoc Disord. 2000 Oct-Dec; 14(4): 231-233.
- Zeman, AZ., Boniface, S.J., & Hodges, J.R. "Transient epileptic amnesia: A description of the clinical and neuropsychological features in 10 cases and a review of the literature. J. Neurol Neurosurg Psychiatry, 64, 435-443.
