Transient global amnesia
Encyclopedia
Transient global amnesia (TGA) is a syndrome in clinical neurology whose key defining characteristic is temporary but almost total disruption of short-term memory with a range of problems accessing older memories. A person in a state of TGA exhibits no other signs of impaired cognitive functioning but recalls only the last few moments of consciousness plus deeply-encoded facts of the individual’s past, such as his or her own name.
The diagnostic criteria for TGA, as defined for purposes of clinical research, include:
, or TIA) is common. In a large survey, 11% of individuals in a TGA state were described as exhibiting "emotionalism" and 14% "fear of dying". The attack lessens over a period of hours, with older memories returning first, and the repetitive fugue slowly lengthening so that the victim retains short-term memory for longer periods. While seemingly back to normal within 24 hours, there are subtle effects on memory that can persist longer. In the majority of cases there are no long-term effects other than a complete lack of recall for this period of the attack and an hour or two before its onset.
There is emerging evidence for observable impairments in a minority of cases weeks or even years following a TGA attack.
There is also evidence that the victim is aware that something is not quite right, even though they can't pinpoint it. The person suffering from the attack may vocalize signs that 'they just lost their memory', or that they believed they had a stroke, although they aren't aware of the other signs that they are displaying. The main sign of this condition is the repetitive actions of something that is not usually repeated.
should include:
If the event lasts less than one hour, transient epileptic amnesia
(TEA) might be implicated.
If the condition lasts longer than 24 hours, it is not considered TGA by definition. A diagnostic investigation would then probably focus on some form of undetected ischemic attack or cranial bleed.
The leading hypotheses are some form of epileptic event, a problem with blood circulation around, to or from the brain, or some kind of migraine-like phenomenon.
The differences are sufficiently meaningful that transient amnesia may be considered a heterogeneous clinical syndrome with multiple etiologies, corresponding mechanisms, and differing prognoses.. Another wildly disputed cause of TGA is excessive contact with bleach products.
If the definition of a precipitating event is widened to include events days or weeks earlier, and to take in emotionally stressful burdens such as money worries, attending a funeral or exhaustion due to overwork or unusual childcare responsibilities, a large majority, over 80%, of TGA attacks are said to correlate with precipitating events.
The role of psychological co-factors has been addressed by some research. It is the case that people in a state of TGA exhibit measurably elevated levels of anxiety and/or depression. Emotional instability may leave some people vulnerable to stressful triggers and thus be associated with TGA. Individuals who have experienced TGA, compared with similar people with TIA, are more likely to have some kind of emotional problem (such as depression or phobias) in their personal or family history or to have experienced some kind of phobic or emotionally challenging precipitating event.
is a frequently-disputed possible cause, at least for some segment of the TGA population, and until the 1990s it was generally thought that TGA was a variant of transient ischemic attack
(TIA) secondary to some form of cerebrovascular disease. Those who argue against a vascular cause point to evidence that those experiencing TGA are no more likely than the general population to have subsequent cerebral vascular disease. In fact, "in comparison with TIA patients, TGA patients had a significantly lower risk of combined stroke, myocardial infarct, and death."
Other vascular origins remain a possibility, however, according to research of jugular vein valve insufficiency in patients with TGA. In these cases, mostly men, TGA has followed vigorous exertion. One current hypothesis is that TGA may be due to venous congestion
of the brain, leading to ischemia
of structures involved with memory, such as the hippocampus
. It has been shown that performing a Valsalva maneuver
(involving ""bearing down"" and increasing breath pressure against a closed glottis, which occurs frequently during exertion) may be related to retrograde flow of blood in the jugular vein, and therefore, presumably, cerebral blood circulation, in patients with TGA.
is a statistically significant risk factor identified in the medical literature. "When comparing TGA patients with normal control subjects… the only factor significantly associated with an increased risk for TGA was migraine." 14% of people with TGA had a history of migraine in one study, and approximately a third of the participants in another clinical study reported such a history.
However, migraine does not appear to occur simultaneously with TGA nor serve as a precipitating event. Headache frequently occurs during TGA, as does nausea, both symptoms often associated with migraine, but it appears that these do not indicate migraine in patients during a TGA event. The connection remains conceptual, and muddied further by a lack of consensus about the definition of migraine itself, and by the differences in age, gender, and psychological characteristics of migraine sufferers when compared to those variables in the TGA cohort.
, and for that reason people with known epilepsy are disqualified from most studies of TGA. In a study where strict criteria were applied to TGA diagnosis, no epileptic features were seen in EEGs of over 100 patients with TGA. However, despite the fact that EEG
readings are usually normal during a TGA attack, and other usual symptoms of epilepsy are not observed with TGA it has been speculated that some initial epileptic attacks present as TGA. The observation that 7% of people who experience TGA will develop epilepsy calls into question whether those case are, in fact, TGA or transient epileptic amnesia
(TEA). TEA attacks tend to be short (under one hour) and tend to recur, so that a person who has experienced both repeated attacks of temporary amnesia resembling TGA and if those events lasted less than one hour is very likely to develop epilepsy.
There is additional speculation that atypical cases of TEA in the form of nonconvulsive status epilepticus
may present with duration similar to TGA. This may constitute a distinct subgroup of TGA.
TEA, as opposed to "pure" TGA, is also characterized by "two unusual forms of memory deficit …: (i) accelerated long-term forgetting (ALF): the excessively rapid loss of newly acquired memories over a period of days or weeks and (ii) remote autobiographical memory loss: a loss of memories for salient, personally experienced events of the past few decades."
Whether an amnestic event is TGA or TEA thus presents a diagnostic challenge, especially in light of the recently-published descriptions of possible long-term cognitive deficits with (presumably correctly-diagnosed) TGA.
s (a class of drug used in treating cholesterol).
"The most important part of management after diagnosis is looking after the psychological needs of the patient and his or her relatives. Seeing a once competent and healthy partner, sibling or parent become incapable of remembering what was said only a minute ago is very distressing, and hence it is often the relatives who will require reassurance."
TGA may have multiple etiologies and prognoses. Atypical presentations may masquerade as epilepsy and be more properly considered TEA. In addition to such probable TEA cases, some people experiencing amnestic events diverging from the diagnostic criteria articulated above may have a less benign prognosis than those with "pure" TGA.
Recently, moreover, both imaging and neurocognitive testing studies question whether TGA is as benign as has been thought. MRI scans of the brain in one study showed that among people who had experienced TGA, all had cavities in the hippocampus, and these cavities were far more numerous, larger, and more suggestive of pathological damage than in either healthy controls or a large control group of people with tumor or stroke. Verbal and cognitive impairments have been observed days after TGA attacks, of such severity that the researchers estimated the effects would be unlikely to resolve within a short time frame. A large neurocognitive study of patients more than a year after their attacks have shown persistent effects consistent with amnestic mild cognitive impairment
(MCI-a) in a third of the people who had experienced TGA. In another study, "selective cognitive dysfunctions after the clinical recovery" were observed, suggesting a prefrontal impairment. These dysfunctions may not be in memory per se but in retrieval, in which speed of access is part of the problem among people who have had TGA and experience ongoing memory problems.
TGA is most common in people between age 56 and 75, with the average age of a person experiencing TGA being approximately 62.
Symptoms
A person having an attack of TGA has almost no capacity to establish new memories, but generally appears otherwise mentally alert and lucid, possessing full knowledge of self-identity and identity of close family, and maintaining intact perceptual skills and a wide repertoire of complex learned behavior. The individual simply cannot recall anything that happened outside the last few minutes, while memory for more temporally distant events may or may not be largely intact. The degree of amnesia is profound, and, in the interval during which the individual is aware of his or her condition, is often accompanied by anxiety.The diagnostic criteria for TGA, as defined for purposes of clinical research, include:
- The attack was witnessed by a capable observer and reported as being a definite loss of recent memory (anterograde amnesiaAnterograde amnesiaAnterograde amnesia is a loss of the ability to create new memories after the event that caused the amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. This is in contrast to retrograde amnesia, where memories...
). - There was an absence of clouding of consciousness or other cognitive impairment other than amnesia.
- There were no focal neurological signs or deficits during or after the attack.
- There were no features of epilepsyEpilepsyEpilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
, or active epilepsy in the past two years, and the patient did not have any recent head injury. - The attack resolved within 24 hours.
Progression of a TGA event
This onset of TGA is generally fairly rapid, and its duration varies but generally lasts between 2 to 8 hours. A person experiencing TGA typically has memory only of the past few minutes or less, and cannot retain new information beyond that period of time. One of its bizarre features is perseverance, in which the victim of an attack faithfully and methodically repeats statements or questions, complete with profoundly identical intonation and gestures "as if a fragment of a sound track is being repeatedly rerun." This is found in almost all TGA attacks and is sometimes considered a defining characteristic of the condition. The individual experiencing TGA retains social skills and older significant memories, almost always including knowing his or her own identity and the identity of family members, and the ability to perform various complex learned tasks including driving and other learned behavior; one individual "was able to continue putting together the alternator of his car." Though outwardly appearing normal, a person in TGA is disoriented in time and space, perhaps knowing neither the year nor where he or she resides. Although confusion is sometimes reported, others consider this an imprecise observation, but an elevated emotional state (compared to patients experiencing Transient Ischemic AttackTransient ischemic attack
A transient ischemic attack is a transient episode of neurologic dysfunction caused by ischemia – either focal brain, spinal cord or retinal – without acute infarction...
, or TIA) is common. In a large survey, 11% of individuals in a TGA state were described as exhibiting "emotionalism" and 14% "fear of dying". The attack lessens over a period of hours, with older memories returning first, and the repetitive fugue slowly lengthening so that the victim retains short-term memory for longer periods. While seemingly back to normal within 24 hours, there are subtle effects on memory that can persist longer. In the majority of cases there are no long-term effects other than a complete lack of recall for this period of the attack and an hour or two before its onset.
There is emerging evidence for observable impairments in a minority of cases weeks or even years following a TGA attack.
There is also evidence that the victim is aware that something is not quite right, even though they can't pinpoint it. The person suffering from the attack may vocalize signs that 'they just lost their memory', or that they believed they had a stroke, although they aren't aware of the other signs that they are displaying. The main sign of this condition is the repetitive actions of something that is not usually repeated.
Differential diagnosis
A differential diagnosisDifferential diagnosis
A differential diagnosis is a systematic diagnostic method used to identify the presence of an entity where multiple alternatives are possible , and may also refer to any of the included candidate alternatives A differential diagnosis (sometimes abbreviated DDx, ddx, DD, D/Dx, or ΔΔ) is a...
should include:
- ThrombosisThrombosisThrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot to prevent blood loss...
of the basilar arteryBasilar arteryIn human anatomy, the basilar artery is one of the arteries that supplies the brain with oxygen-rich blood.The two vertebral arteries and the basilar artery are sometimes together called the vertebrobasilar system, which supplies blood to the posterior part of circle of Willis and anastomoses with... - Cardioembolic strokeStrokeA stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
- Complex partial seizures
- Frontal lobe epilepsyFrontal lobe epilepsyFrontal lobe epilepsy, or FLE, is a neurological disorder that is characterized by brief, recurring seizures that arise in the frontal lobes of the brain, often while the patient is sleeping...
- Lacunar syndromes
- MigraineMigraineMigraine is a chronic neurological disorder characterized by moderate to severe headaches, and nausea...
variants - Posterior cerebral arteryPosterior cerebral artery-External links: - Posterior Cerebral Artery Stroke* at strokecenter.org* at State University of New York Upstate Medical University* at psyweb.com* at neuropat.dote.hu...
stroke - SyncopeSyncope (medicine)Syncope , the medical term for fainting, is precisely defined as a transient loss of consciousness and postural tone characterized by rapid onset, short duration, and spontaneous recovery due to global cerebral hypoperfusion that most often results from hypotension.Many forms of syncope are...
and related paroxysmal spells - Temporal lobe epilepsyTemporal lobe epilepsyTemporal lobe epilepsy a.k.a. Psychomotor epilepsy, is a form of focal epilepsy, a chronic neurological condition characterized by recurrent seizures. Over 40 types of epilepsies are known. They fall into two main categories: partial-onset epilepsies and generalized-onset epilepsies...
If the event lasts less than one hour, transient epileptic amnesia
Transient epileptic amnesia
Transient epileptic amnesia is a rare but probably underdiagnosed neurological condition which manifests as relatively brief and generally recurring episodes of amnesia caused by underlying temporal lobe epilepsy...
(TEA) might be implicated.
If the condition lasts longer than 24 hours, it is not considered TGA by definition. A diagnostic investigation would then probably focus on some form of undetected ischemic attack or cranial bleed.
Causes
The underlying cause of TGA remains enigmatic.The leading hypotheses are some form of epileptic event, a problem with blood circulation around, to or from the brain, or some kind of migraine-like phenomenon.
The differences are sufficiently meaningful that transient amnesia may be considered a heterogeneous clinical syndrome with multiple etiologies, corresponding mechanisms, and differing prognoses.. Another wildly disputed cause of TGA is excessive contact with bleach products.
Precipitating events
TGA attacks are associated with some form of precipitating event in at least one-third of cases. In females, this event is more often of a strong emotional character; in males, it is more often related to some physical exertion. The most commonly cited precipitating events include vigorous exercise (including sexual intercourse), swimming in cold water or enduring other temperature changes, and emotionally traumatic or stressful events. There are reports of TGA-like conditions following certain medical procedures and disease states. There is a slight (2%) familial incidence.If the definition of a precipitating event is widened to include events days or weeks earlier, and to take in emotionally stressful burdens such as money worries, attending a funeral or exhaustion due to overwork or unusual childcare responsibilities, a large majority, over 80%, of TGA attacks are said to correlate with precipitating events.
The role of psychological co-factors has been addressed by some research. It is the case that people in a state of TGA exhibit measurably elevated levels of anxiety and/or depression. Emotional instability may leave some people vulnerable to stressful triggers and thus be associated with TGA. Individuals who have experienced TGA, compared with similar people with TIA, are more likely to have some kind of emotional problem (such as depression or phobias) in their personal or family history or to have experienced some kind of phobic or emotionally challenging precipitating event.
Vascular hypotheses
Cerebral ischemiaCerebral ischemia
Brain ischemia, also known as cerebral ischemia, is a condition in which there is insufficient blood flow to the brain to meet metabolic demand. This leads to poor oxygen supply or cerebral hypoxia and thus to the death of brain tissue or cerebral infarction / ischemic stroke...
is a frequently-disputed possible cause, at least for some segment of the TGA population, and until the 1990s it was generally thought that TGA was a variant of transient ischemic attack
Transient ischemic attack
A transient ischemic attack is a transient episode of neurologic dysfunction caused by ischemia – either focal brain, spinal cord or retinal – without acute infarction...
(TIA) secondary to some form of cerebrovascular disease. Those who argue against a vascular cause point to evidence that those experiencing TGA are no more likely than the general population to have subsequent cerebral vascular disease. In fact, "in comparison with TIA patients, TGA patients had a significantly lower risk of combined stroke, myocardial infarct, and death."
Other vascular origins remain a possibility, however, according to research of jugular vein valve insufficiency in patients with TGA. In these cases, mostly men, TGA has followed vigorous exertion. One current hypothesis is that TGA may be due to venous congestion
Congestion
Congestion generally means excessive crowding.Congestion may refer to:* congestion in heart failure, a term to describe low cardiac output seen in heart failure.* Nasal congestion, the blockage of nasal passages due to swollen membranes...
of the brain, leading to ischemia
Ischemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
of structures involved with memory, such as the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
. It has been shown that performing a Valsalva maneuver
Valsalva maneuver
The Valsalva maneuver or Valsalva manoeuvre is performed by moderately forceful attempted exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut...
(involving ""bearing down"" and increasing breath pressure against a closed glottis, which occurs frequently during exertion) may be related to retrograde flow of blood in the jugular vein, and therefore, presumably, cerebral blood circulation, in patients with TGA.
Migraine
A history of migraineMigraine
Migraine is a chronic neurological disorder characterized by moderate to severe headaches, and nausea...
is a statistically significant risk factor identified in the medical literature. "When comparing TGA patients with normal control subjects… the only factor significantly associated with an increased risk for TGA was migraine." 14% of people with TGA had a history of migraine in one study, and approximately a third of the participants in another clinical study reported such a history.
However, migraine does not appear to occur simultaneously with TGA nor serve as a precipitating event. Headache frequently occurs during TGA, as does nausea, both symptoms often associated with migraine, but it appears that these do not indicate migraine in patients during a TGA event. The connection remains conceptual, and muddied further by a lack of consensus about the definition of migraine itself, and by the differences in age, gender, and psychological characteristics of migraine sufferers when compared to those variables in the TGA cohort.
Epilepsy
Amnesia is often a symptom in epilepsyEpilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
, and for that reason people with known epilepsy are disqualified from most studies of TGA. In a study where strict criteria were applied to TGA diagnosis, no epileptic features were seen in EEGs of over 100 patients with TGA. However, despite the fact that EEG
EEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...
readings are usually normal during a TGA attack, and other usual symptoms of epilepsy are not observed with TGA it has been speculated that some initial epileptic attacks present as TGA. The observation that 7% of people who experience TGA will develop epilepsy calls into question whether those case are, in fact, TGA or transient epileptic amnesia
Transient epileptic amnesia
Transient epileptic amnesia is a rare but probably underdiagnosed neurological condition which manifests as relatively brief and generally recurring episodes of amnesia caused by underlying temporal lobe epilepsy...
(TEA). TEA attacks tend to be short (under one hour) and tend to recur, so that a person who has experienced both repeated attacks of temporary amnesia resembling TGA and if those events lasted less than one hour is very likely to develop epilepsy.
There is additional speculation that atypical cases of TEA in the form of nonconvulsive status epilepticus
Status epilepticus
Status epilepticus is a life-threatening condition in which the brain is in a state of persistent seizure. Definitions vary, but traditionally it is defined as one continuous unremitting seizure lasting longer than 5 minutes, or recurrent seizures without regaining consciousness between seizures...
may present with duration similar to TGA. This may constitute a distinct subgroup of TGA.
TEA, as opposed to "pure" TGA, is also characterized by "two unusual forms of memory deficit …: (i) accelerated long-term forgetting (ALF): the excessively rapid loss of newly acquired memories over a period of days or weeks and (ii) remote autobiographical memory loss: a loss of memories for salient, personally experienced events of the past few decades."
Whether an amnestic event is TGA or TEA thus presents a diagnostic challenge, especially in light of the recently-published descriptions of possible long-term cognitive deficits with (presumably correctly-diagnosed) TGA.
Other putative associations
There have been assertions of a possible link between TGA and the use of statinStatin
Statins are a class of drugs used to lower cholesterol levels by inhibiting the enzyme HMG-CoA reductase, which plays a central role in the production of cholesterol in the liver. Increased cholesterol levels have been associated with cardiovascular diseases, and statins are therefore used in the...
s (a class of drug used in treating cholesterol).
Prognosis
The prognosis of "pure" TGA is very good. It does not affect mortality or morbidity and unlike earlier understanding of the condition, TGA is not a risk factor for stroke or ischemic disease. Rates of recurrence are variously reported, with one systematic calculation suggesting the rate is under 6% per year. TGA “is universally felt to be a benign condition which requires no further treatment other than reassurance to the patient and their family.”"The most important part of management after diagnosis is looking after the psychological needs of the patient and his or her relatives. Seeing a once competent and healthy partner, sibling or parent become incapable of remembering what was said only a minute ago is very distressing, and hence it is often the relatives who will require reassurance."
TGA may have multiple etiologies and prognoses. Atypical presentations may masquerade as epilepsy and be more properly considered TEA. In addition to such probable TEA cases, some people experiencing amnestic events diverging from the diagnostic criteria articulated above may have a less benign prognosis than those with "pure" TGA.
Recently, moreover, both imaging and neurocognitive testing studies question whether TGA is as benign as has been thought. MRI scans of the brain in one study showed that among people who had experienced TGA, all had cavities in the hippocampus, and these cavities were far more numerous, larger, and more suggestive of pathological damage than in either healthy controls or a large control group of people with tumor or stroke. Verbal and cognitive impairments have been observed days after TGA attacks, of such severity that the researchers estimated the effects would be unlikely to resolve within a short time frame. A large neurocognitive study of patients more than a year after their attacks have shown persistent effects consistent with amnestic mild cognitive impairment
Mild cognitive impairment
Mild cognitive impairment is a brain-function syndrome involving the onset and evolution of cognitive impairments beyond those expected based on the age and education of the individual, but which are not significant enough to interfere with their daily activities...
(MCI-a) in a third of the people who had experienced TGA. In another study, "selective cognitive dysfunctions after the clinical recovery" were observed, suggesting a prefrontal impairment. These dysfunctions may not be in memory per se but in retrieval, in which speed of access is part of the problem among people who have had TGA and experience ongoing memory problems.
Epidemiology
The estimated annual incidence of TGA varies from a minimum of 2.9 cases per 100,000 population (in Spain) and 5.2 per 100,000 (in USA), but among people aged over 50, the rate of TGA incidence is reported to range from approximately 23 per 100,000 (in a US population) to 32 per 100,000 (in a population in Scandinavia).TGA is most common in people between age 56 and 75, with the average age of a person experiencing TGA being approximately 62.