Transient global amnesia (TGA) refers to a benign episode of memory loss of unknown aetiology, which resolves spontaneously within 24 hours.
A typical feature is an inability to retain new information and, to some degree, to recall events from the past few days whilst cognitive functioning and the level of consciousness are unaffected.
The clinical picture is usually obvious and no follow-up investigations or treatment are needed after a short observation period.
Epidemiology
Usually encountered in late middle-age, the average age being about 60 years
More common in women
Aetiology
Associated with a local dysfunction of the hippocampus, but the precise mechanism or causative factors remain elusive.
Migraine equivalent, an epileptic mechanism and cerebrovascular disease, i.e. a mechanism resembling a TIA, have all been postulated to account for TGA.
More common in individuals with migraine.
Emotional stress and a sensitive personality may predispose a person to TGA, particularly after an exposure to a prolonged Valsalva phenomenon, which can result for example from severe straining, exposure to cold temperature or acute pain.
The increase in intrathoracic pressure that occurs during the Valsalva phenomenon reduces intracranial venous return. Venous congestion, caused by the reduction in venous return, could result in ischaemia of the basal structures of the brain involved with memory, in which case a haemodynamic disturbance would be the principal cause of the disorder.
Not one of the mechanisms proposed so far can explain all the cases encountered, and it is therefore likely that several underlying mechanisms and/or predisposing structural factors exert a simultaneous effect.
Signs and symptoms
The principal symptom is an abrupt onset of anterograde amnesia, i.e. an inability to retain new information. The patient will, therefore, ask repetitive questions. Moreover, some degree of retrograde amnesia will be present.
However, the level of consciousness, behaviour, the patient's own identity, remembering the names of close family members and cognitive functioning remain intact.
Neurological examination is normal.
Diagnosis
Diagnosis is based solely on a clinical assessment; laboratory or imaging studies will not yield additional information. Nevertheless, diagnosis is usually easy since no other neurological condition has this type of symptom picture.
If the clinical picture is not entirely typical, for example, if in addition to the loss of memory the patient exhibits other neurological symptoms or the neurological examination reveals side differences or abnormalities, or if the episode lasts for more than 24 hours or recurs, relevant additional investigations should be considered, such as imaging studies of the head and/or an EEG.
Treatment and prognosis
The patient is normally monitored in hospital, usually in the emergency department, until the memory disturbance resolves.
No actual treatment is available, but the condition will resolve spontaneously and completely within 24 hours. However, a permanent gap will remain in the patient's memory, equal to the length of time that the amnesia lasted.
The condition usually causes no anxiety to the patient, but in order to reassure family members or those accompanying the patient they should be informed of the benign nature of TGA, and of the fact that it only seldom recurs and it is not a risk factor, for example, for cerebrovascular disease.
The episode may recur in slightly more than 10% of patients.
Younger age (below 60 years) at the time of the first episode, as well as history of migraine predispose to recurrence.
In the case of recurrence, actions should be taken case by case, excluding other, alternative diagnoses, as necessary.
References
Liampas I, Siouras AS, Siokas V et al. Migraine in transient global amnesia: a meta-analysis of observational studies. J Neurol 2021;():. [PubMed]
Morris KA, Rabinstein AA, Young NP. Factors Associated With Risk of Recurrent Transient Global Amnesia. JAMA Neurol 2020;77(12):1551-1558. [PubMed]