Elsevier

Mayo Clinic Proceedings

Volume 90, Issue 2, February 2015, Pages 264-272
Mayo Clinic Proceedings

Review
Transient Global Amnesia

https://doi.org/10.1016/j.mayocp.2014.12.001Get rights and content

Abstract

Transient global amnesia (TGA) is a clinical syndrome characterized by the sudden onset of anterograde amnesia (the inability to encode new memories), accompanied by repetitive questioning, sometimes with a retrograde component, lasting up to 24 hours, without compromise of other neurologic functions. Herein, we review current knowledge on the epidemiology, pathophysiology, clinical diagnosis, and prognosis of TGA. For this review, we conducted a literature search of PubMed, with no date limitations, using the following search terms (or combinations of them): transient global amnesia, etiology, pathophysiology, venous hypertension, migraine, magnetic resonance imaging, computed tomography, electroencephalography, prognosis, and outcome. We also reviewed the bibliography cited in the retrieved articles. Transient global amnesia is a clinical diagnosis, and recognition of its characteristic features can avoid unnecessary testing. Several pathophysiologic mechanisms have been proposed (venous insufficiency, arterial ischemia, and migrainous or epileptic phenomena), but none of them has been proved to consistently explain cases of TGA. Brain imaging may be considered and electroencephalography is recommended when episodes are brief and recurrent, but otherwise no investigations are necessary in most cases. Data on long-term prognosis are limited, but available information suggests that the relapse rate is low, the risk of stroke and seizures is not considerably increased, and cognitive outcome is generally good.

Section snippets

Basic Concepts on Memory

Memory is the brain function that allows us to encode, store, and retrieve information. It can be divided into 3 different types: immediate or working memory, short-term memory, and long-term memory.13 Immediate memory refers to the information that can be retained for a short period of time without active involvement of the memory pathways. It can be simply tested by asking the patient to repeat a 7-digit number. This type of memory can be affected by attention or language impairment or by a

Epidemiologic Profile

Transient global amnesia affects predominantly middle-aged or elderly patients. Its annual incidence has been reported to be 3.4 to 10.4 per 100,000 people.6, 14, 15, 16 If we narrow it to the population older than 50 years, the incidence increases to 23.5 per 100,000 per year.17 It is more common in individuals with migraine.18, 19

Clinical Presentation and Diagnostic Criteria

Transient global amnesia is a clinical syndrome characterized by the sudden onset of anterograde amnesia, accompanied by repetitive questioning, sometimes with a retrograde component, lasting up to 24 hours, and without compromise of other neurologic functions. Typically, TGA is encountered in patients aged 50 to 70 years who are brought to medical attention because they are noticed to have acutely lost the ability to understand their situation and grasp their surroundings. Patients repeatedly

Additional Investigations

When making a diagnosis of TGA, the question is whether to pursue additional testing. The main value of additional testing in TGA is to exclude alternative diagnoses.

Brain imaging is often considered by clinicians who suspect TGA, but findings from head computed tomography are typically normal, and evidence on the utility of brain magnetic resonance imaging (MRI) is conflicting. Case series and studies comparing patients with TGA and those with transient ischemic attack (TIA) or control cohorts

Differential Diagnosis

The differential diagnosis of TGA includes TIA or stroke in the posterior cerebral circulation, focal seizures (including TEA), postictal state, dissociative disorders or psychogenic amnesia, posttraumatic amnesia, and metabolic disorders such as hypoglycemia. The differentiating features of some of these alternative diagnoses are reviewed on Table 2. It is particularly important to remember that isolated memory loss is a very infrequent presentation of acute ischemic stroke. Meanwhile,

Pathophysiologic Mechanisms

The debate regarding the pathogenesis of TGA has focused mainly on 3 distinct mechanisms: vascular (due to venous flow disturbances or focal arterial ischemia), epileptic, and migraine related. It has also been reported that the CA1 subfield of the hippocampal cornu ammonis (which is the part of the hippocampus most affected by TGA) would have a particular vulnerability to metabolic stress caused by hypoxemia, B-amyloid–induced neurotoxicity, and ischemia; the degree of this local

Treatment

There is no specific treatment for TGA. Episodes are self-limited, and improvement is noted within 24 hours without any intervention. It seems prudent to avoid any activity that could raise intrathoracic venous pressure until the amnesia is resolved. When alternative diagnoses are suspected (eg, seizures or ischemic stroke/TIA), focused investigations should be pursued to determine whether acute treatment or secondary prevention for these disorders might be indicated.

Long-term Outcome in Patients With TGA

Transient global amnesia is generally considered a benign condition. However, there are few studies on the long-term outcome of patients who have experienced TGA regarding the risk of recurrence and the incidence of cognitive decline, stroke, and seizures over time.

Reported recurrence rates for TGA have varied considerably (between 2.9% and 23.8%) among different studies (Table 3). The reason for such a spread in the rate of recurrences found in different studies is unclear. There is no

Conclusion

Transient global amnesia is not a rare condition. It typically presents in patients aged 50 to 70 years, and it is frequently preceded by a Valsalva maneuver. Diagnosis is clinical, and its semiological hallmark is the inability to form new memories, although some retrograde amnesia can occasionally be present. Noncognitive functions are always preserved, and the presence of aphasia, hemiparesis, sensory loss, or incoordination indicates a different diagnosis and demands additional evaluation.

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