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Syndromes of Transient Amnesia


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									                                                                                                                                                           Review Article

Syndromes of Transient Amnesia

      or most of us, transient lapses of memory are a                    ly occurs within 4 to 10 hours, although the individual
      familiar and at worst irritating feature of daily life.            is left with a permanent amnesic gap for the duration of
      They are generally brief, item specific and alleviat-              the attack. Recurrence is rare, with most recent studies
ed by a pertinent cue. At the other extreme, the amnesic                 reporting a rate of between 3 and 10% per year. A sin-
syndrome is characterised by a profound and usually                      gle, uncomplicated episode requires minimal investiga-
permanent loss of the ability both to retrieve previous-                 tion and no specific treatment.
ly established memories (retrograde amnesia) and to                         It is widely accepted that the pathological changes in
form new ones (anterograde amnesia). A permanent                         TGA affect the medial temporal lobes, although pre-
amnesic syndrome is usually caused by extensive bilat-                   cisely what those pathological changes are and why                         Chris Butler is a trainee neurolo-
eral damage to the medial temporal lobes (as in limbic                   they occur is far from resolved. A number of studies                       gist from Edinburgh, UK who has
encephalitis or post-hypoxic damage) or to the dien-                     have reported increased prevalence of migraine                             recently completed a three-year
cephalon (as in Korsakoff ’s syndrome), brain regions                    amongst TGA patients3 and migrainous accompani-                            project investigating the clinical
                                                                                                                                                    and neuropsychological features
which play a key role in declarative, ‘conscious’ memory                 ments, including headache, nausea and vomiting, are                        of transient epileptic amnesia. He
for facts and events.1 Some people, however, experience                  not uncommon during the amnesic period. This mech-                         is currently conducting post-doc-
an episode of dense memory loss which is sudden in                       anism alone, however, would not explain the limited                        toral research, with an emphasis
onset but self-limiting. These syndromes of transient                    age range and rare recurrence of TGA. More recent                          on functional imaging in neurode-
                                                                                                                                                    generative disease and epilepsy, at
amnesia are the focus of this article.                                   studies using diffusion-weighted imaging have revealed                     the Memory and Aging Center,
                                                                         punctate hippocampal lesions, supportive of a vascular                     UC San Francisco, USA.
Transient Global Amnesia (TGA)                                           aetiology, in a significant proportion of TGA cases.4,5
The syndrome of TGA has an incidence of 3 to 10 per                      Interestingly, given the frequency of Valsalva manoeu-
100,000 and is characterised by the abrupt onset, usual-                 vre-like precipitants in TGA, it has also been found that
ly in middle to old age, of a profound but transient                     patients have a higher prevalence of jugular vein
deficit in the retention of new information together                     incompetence than controls,6,7 lending support to a
with a variable degree of amnesia for past events.2 At                   hypothesis that increased pressure in the superior vena
least 50% of cases appear to be precipitated by a variety                cava causes ischaemia in crucial memory-related brain
of acute stressors including exercise, immersion in cold                 structures.8
water, sexual intercourse, pain, or a strongly emotional                    Episodes of transient amnesia occurring in the con-
event. The anterograde amnesia is betrayed by repetitive                 text of epilepsy or head injury and those accompanied
                                                                                                                                                    Adam Zeman is Professor of
questioning, usually related to attempts at self-orienta-                by focal neurological symptoms or signs are usually                        Clinical and Behavioural Neuro-
tion such as “What day is it?” or “What am I doing                       excluded from the rubric of TGA (see Table 1). These                       logy at the Peninsula Medical
here?” The retrograde amnesia may cover a few hours                      are discussed below.                                                       School, UK. His research interests
prior to the attack onset or be much more extensive.                                                                                                include the impairment of memo-
                                                                                                                                                    ry in epilepsy, disorders of cogni-
There is no impairment of consciousness or of other                      Transient Epileptic Amnesia (TEA)                                          tion and emotion associated with
cognitive functions such as attention, language or per-                  TEA is a relatively recently described condition in which                  cerebellar disease and the interdis-
ception, and there are no focal neurological deficits.                   transient amnesia is the principal manifestation of tem-                   ciplinary study of consciousness.
Spontaneous and apparently complete recovery typical-                    poral lobe seizures.9,10 The attacks are often mistaken for
                                                                                                                                                    Correspondence to:
                                                                                                                                                    Christopher R Butler,
   Table 1: Diagnostic criteria                                             Table 2: Characteristic features                                        Visiting Postdoctoral Scholar in
  Transient Global Amnesia (Hodges and Warlow 1993)                                                                                                 Memory and Aging Center,
                                                                           TGA                                                                      University of California,
  1. attacks must be witnessed and information available from a            • sudden onset often precipitated by exercise, immersion in              San Francisco, Suite 706,
     capable observer who was present for most of the attack                 water, emotional stress, etc                                           350 Parnassus Avenue,
                                                                                                                                                    San Francisco,
  2. there must be a clear-cut anterograde amnesia during                  • dense anterograde amnesia with repetitive questioning                  California 94143, USA.
     the attack                                                            • lasts around 4 – 10 hours                                              Email: cbutler@memory.ucsf.edu
  3. clouding of consciousness and loss of personal identity must          • rarely recurs
     be absent, and the cognitive deficit must be limited to                                                                                        Adam ZJ Zeman,
                                                                           • aetiology unknown                                                      Professor of Cognitive and
     amnesia (that is, no aphasia, apraxia, etc)                                                                                                    Behavioural Neurology,
  4. there should be no accompanying focal neurological                                                                                             Peninsula Medical School,
                                                                           TEA                                                                      Mardon Centre,
     symptoms during the attack and no significant neurological
     signs afterwards                                                      • recurrent, brief (usually < 1 hour) amnesic episodes                   Exeter EX2 4UD, UK.
                                                                           • often occur upon waking                                                Email: adamzeman@pms.ac.uk
  5. epileptic features must be absent
  6. attacks must resolve within 24 hours                                  • may be associated with olfactory hallucinations or
  7. patients with recent head injury or active epilepsy (that is,
     remaining on medication or one seizure in the past two years)         • responds to anticonvulsant medication
     are excluded                                                          • persistent memory deficits

  Transient Epileptic Amnesia (Zeman et al 1998)
                                                                           Psychogenic amnesia
  1. a history of recurrent witnessed episodes of transient amnesia
                                                                           • history of ‘organic amnesia’, psychiatric illness and/or
  2. cognitive functions other than memory judged to be intact               substance abuse
     during typical episodes by a reliable witness
                                                                           • may be triggered by mild head injury or highly
  3. evidence for a diagnosis of epilepsy based on one or more of            emotional event
     the following:
                                                                           • extensive retrograde amnesia often with loss of personal
        a. epileptiform abnormalities on electroencephalography              identity
        b. the concurrent onset of other clinical features of epilepsy     • preserved new learning
             (e.g. lip-smacking, olfactory hallucinations)
                                                                           • duration usually several days at least
        c. a clear-cut response to anticonvulsant therapy.

                                                                                                                                    ACNR • VOLUME 6 NUMBER 4 • SEPTEMBER/OCTOBER 2006   I 13
Review Article

                                                                                                                  Age of memory (years)
Figure 1: MRI scan showing the location of the hippocampus and      Figure 2: Autobiographical amnesia in TEA. When asked to produce personal memories relating to a particular word
parahippocampal gyrus in the medial temporal lobes. These areas     (eg ‘boat’), a 68-year-old TEA patient failed to retrieve any episodes from his 20’s or 30’s. His performance on
are crucial for the processing of declarative memories.             standard tests of anterograde memory was normal.

TGA. They too occur in late-middle to old age                 brovascular events.14 However, some transient
and usually involve a mixed anterograde and                   ischaemic attacks, particularly of the posteri-
retrograde amnesia, repetitive questioning                    or circulation, can result in a transient mem-
and otherwise preserved cognitive function-                   ory disturbance that resembles TGA. In these
ing. However, there are a number of impor-                    cases, the physician should be alerted by
tant distinguishing features. The attacks are                 accompanying neurological signs such as                     References
recurrent and tend to be briefer than TGA,                    ataxia, dysarthria, nystagmus or hemianopia.2               1. O’Connor M, Verfaellie M. The Amnesic Syndrome:
                                                                                                                              Overview and Subtypes. In: Baddeley AD, Kopelman
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ated with other features suggestive of epilepsy               Memory is a psychological function and dis-                 2. Hodges JR. Transient amnesia. London: WB Saunders,
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                                                                                                                              Neurol Neurosurg Psychiatry 1990;53(10):834-43.
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                                                                                                                          4. Sedlaczek O, Hirsch JG, Grips E, Peters CN, Gass A,
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