Transient Global Amnesia

This Mysterious Disorder Temporarily Disrupts Memory

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A 56 year-old man began acting strangely shortly after arriving at a baseball game with his wife. She noticed that he began repeating parts of the conversation that had just happened a few minutes ago. He did not seem to remember how he had gotten to the game.

Frightened and worried that he might be having a stroke, she took him to the emergency room. Doctors looked for signs of stroke and seizure, but found nothing wrong.

Over the course of the next day, the man returned to his normal self, with little memory of what had occurred.

Naturally, both he and his wife were concerned that this might be something serious, or that it could happen again.

What Is Transient Global Amnesia?

Transient global amnesia (TGA) is a mysterious syndrome causing a relatively brief inability to form new memories. It usually happens in people who are middle-aged or elderly. The disorder is relatively rare, occurring in about 23.5 to 32 per 100,000 people per year in those over the age of 50.

People with TGA frequently repeat the same question, as they may not remember more than a few minutes at a time. The problem usually lasts from one to ten hours. In addition to the inability to form new memories (anterograde amnesia), there is often some degree of retrograde amnesia, meaning an inability to remember things that have occurred in the past, reaching back anywhere from hours to, rarely, years.

People with TGA are still able to state who they are, and remember how to perform complicated tasks such as driving or cooking. While amnesia is the most prominent feature, some patients complain of headache, nausea, dizziness or other symptoms during an episode of TGA.

Sometimes TGA may be triggered by emotional events.

Postural changes, high altitude, strenuous exercise or bearing down may also precipitate an episode.

While TGA only repeats itself about 15 percent of the time and does not necessarily indicate a more serious problem, similar memory lapses can also result from seizure or stroke, making it important to be evaluated quickly.

The Cause of TGA

The cause of TGA is still unknown, but the symptoms suggest dysfunction in the medial temporal lobe, the area of the brain that contains the hippocampus and is critical for formation of new memories. Some studies have shown lesions in this area in those suffering from TGA, but these lesions do not seem quite like those normally associated with stroke, as they often disappear.

Theories include a transient change in blood flow to these regions, or perhaps a migrainous phenomenon involving slow changes in electrical activity. It is possible that the syndrome results from more than one cause.

While transient decrease in blood flow (a transient ischemic attack or "TIA") to the hippocampus can mimic TGA, TGA usually lasts longer than a typical transient ischemic attack.

There is no clear relationship between stroke risk factors and TGA.

Some studies suggest that migraine is associated with TGA. While it is best known for causing headaches, migraine phenomena can actually cause a wide range of transient neurological deficits due to a slow wave of electrical activity across the brain. Migraine can cause the MRI changes seen in TGA cases, and the time-course for migraine attacks and TGA is similar. Migraines, though, impact people at many ages, especially younger, whereas TGA impacts middle to older aged people.

Initially, some doctors suspected that TGA may be a psychiatric disorder with no clear underlying brain problem, but the lack of other psychiatric symptoms in patients and similar presentation across so many different people makes this unlikely.

Management of TGA

TGA itself requires no treatment, as the episode will usually pass within 24 hours. It is not uncommon to hospitalize someone for TGA, however, in order to ensure that a more serious problem isn't causing the symptoms. For example, while there is no specific treatment, patients should receive thiamine to exclude Wernicke's encephalopathy, a type of memory loss due to insufficient levels of the vitamin thiamine.

The differential diagnosis includes seizures arising from the mesial temporal lobe. For this reason, getting an electroencephalogram (EEG) is a good idea, though a normal EEG does not exclude the possibility of subtle seizure activity too deep to be detected by the scalp electrodes. If there is high concern for seizure, prolonged EEG may be advisable, preferably one that captures a period of sleep.

A transient ischemic attack or stroke can imitate TGA, though this is uncommon without other symptoms such as weakness or numbness. An MRI may be used to exclude this possibility, especially if someone has serious vascular risk factors such as diabetes, high cholesterol, high blood pressure or smoking.

Psychogenic amnesia is a type of conversion disorder, meaning that a psychiatric complaint manifests as a more physical deficit. Unlike TGA, patients with psychogenic amnesia forget their name or other pieces of autobiographical information. Other serious things to be considered with TGA include low blood sugar, alcohol or drug use or withdrawal, encephalitis, or delirium, though these cases usually present with a less specific confusion rather than just memory loss.

Prognosis

People with TGA do not seem to be at an increased risk of stroke or other serious vascular disease. Some studies have suggested that subtle memory deficits may linger after an episode, though others have found no such association.

Even though the work-up for the gentleman described showed no sign of stroke or seizure, it is normal to be concerned about the possibility of a recurrence of symptoms. Such a recurrence is uncommon, but not impossible, and should prompt further evaluation for other possible explanations.

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