Transient global amnesia is characterized by sudden-onset anterograde and retrograde amnesia that typically lasts up to 24 hours. Diagnosis is primarily clinical, but laboratory and imaging studies are done to exclude other disorders. The amnesia typically remits spontaneously but may recur. There is no specific treatment unless an underlying condition is present.
The annual incidence of transient global amnesia is between 3.4 and 10.4/100 000. Most cases of transient global amnesia occur in people aged 50 to 70; this disorder rarely occurs in people < 50. It affects men slightly more often than women (1).
Reference
1. Miller TD, Butler CR: Acute-onset amnesia: Transient global amnesia and other causes. Pract Neurol 22 (3):201–208, 2022. doi: 10.1136/practneurol-2020-002826 Epub 2022 May 3.
Etiology of Transient Global Amnesia
The etiology of transient global amnesia is not clear. Suggested mechanisms include those related to migraine, hypoxia and/or ischemia, venous flow abnormalities, or seizures, as well as psychologic factors.
Recent data suggest that vulnerability of neurons in the CA1 area of the hippocampus to metabolic stress is pivotal; the resulting damage triggers a cascade of changes that lead to impaired hippocampal function.
Events that can trigger transient global amnesia include
Sudden immersion in cold or hot water
Physical exertion
Emotional or psychologic stress
Pain
Medical procedures
Sexual intercourse
A Valsalva maneuver
However, usually no trigger can be identified.
Symptoms and Signs of Transient Global Amnesia
The classic presentation in transient global amnesia is
Abrupt onset of severe anterograde amnesia
But a less severe retrograde amnesia may be the presenting symptom.
Episodes usually last for 1 to 8 hours but may last from 30 minutes to 24 hours (rarely). Patients are often disoriented to time and place but usually not to personal identity. Many patients are anxious or agitated and may repeatedly ask questions about transpiring events (eg, "Where are we?" or “What happened?"). Language function, attention, visual-spatial skills, and social skills are retained. Impairments gradually resolve as the episode subsides.
The benign transient amnesia after substance ingestion is distinct because it
Is selectively retrograde (ie, for events during and preceding intoxication)
Relates specifically to drug-accompanied events
Does not cause confusion (once acute intoxication resolves)
Recurs only if similar amounts of the same drug are ingested
Diagnosis of Transient Global Amnesia
Primarily clinical evaluation
Brain imaging
Diagnosis of transient global amnesia is primarily clinical. Neurologic examination typically does not detect any abnormalities other than disturbed memory. Brain ischemia must be ruled out.
Laboratory tests should include complete blood count (CBC), coagulation tests, and evaluation for hypercoagulable states. These tests can help rule out other possible causes of the amnesia (eg, severe anemia, clotting disorders).
MRI of the brain done during an episode of transient global amnesia is usually normal; however, MRI is useful for excluding stroke or a space-occupying lesion. MRI is most useful after the amnestic period has resolved. Why lesions are more visible later, when the patient has recovered, is unknown.
Electroencephalography (EEG) is done to check for seizure activity. It usually shows nonspecific abnormalities and is unnecessary unless a seizure is suspected or episodes recur.
The following conditions should be ruled out before diagnosing transient global amnesia:
Acute ischemic stroke involving the hippocampus
Transient epileptic amnesia
Psychogenic amnesia
Toxin- or drug-related amnesia
Posttraumatic amnesia
A more extensive evaluation may be done if the transient amnestic episodes recur.
Treatment of Transient Global Amnesia
Treatment of any underlying condition as needed
No specific treatment is indicated for transient global amnesia. However, any underlying condition (eg, brain ischemia) should be treated.
Prognosis for Transient Global Amnesia
Prognosis is good. Symptoms typically last < 24 hours. As the disorder resolves, the amnesia lessens, but memory for events during the episode may be lost.
Although transient global amnesia usually does not recur, approximately 15% of patients have more than one episode.
Risk of stroke is not increased.
Key Points
Transient global amnesia usually affects patients aged 50 to 70.
Do high-resolution diffusion-weighted brain MRI to exclude an underlying condition (eg, brain ischemia) as a cause of the symptoms.
Although memories that were lost may not be recovered, memory function tends to resolve within 24 hours, and episodes usually do not recur.
