Transient global amnesia is a rare condition that affects about five out 100,000 people per year. The experience can be frightening for both the person experiencing it and those who are present when it occurs. While experts have not identified a specific cause, some common triggers occur in people who have had transient global amnesia. Luckily, the condition resolves on its own within 24 hours and does not seem to have any long-lasting effects.
Transient global amnesia (TGA) is a temporary short term memory loss that occurs suddenly and is not caused by another neurological event such as a stroke or epilepsy. During an episode, the person becomes suddenly confused about where they are and what they are doing there. They may ask the same questions over and over because they cannot remember the answers they were just given. Otherwise, they are alert and seem to be thinking normally.
While transient global amnesia and dementia share some characteristics, they are different conditions. People with dementia are often confused about who they are and may not recognize the people around them, but those experiencing TGA retain much of this knowledge: who they are, who friends and family are, and how to perform complex tasks. No memories are formed during the episode and the person has no recollection of the experience after it passes.
The defining characteristic of transient global amnesia is the sudden onset of the inability to form new memories or recall short term memories. For an official diagnosis of TGA, a witness must verify this sudden onset. The affected individual must retain their identity and be able to follow simple directions and recognize familiar objects. Finally, there cannot be any signs of impairment or damage to the brain, such as involuntary movements, facial drooping, or limb paralysis, which are more likely to indicate a stroke.
Short term memory loss or prominent anterograde amnesia is the main symptom of TGA. The person often asks the same questions over and over because they are confused and cannot remember the answers they receive. People experiencing TGA are often described as "sounding like a broken record" because of this repetition. The memories lost during an episode can span hours, days, or weeks.
Other factors can help diagnose transient global amnesia as well. Memory loss typically only lasts between one and eight hours. Six hours is the average length of time, and episodes last no longer than 24. When the memory returns, it comes back gradually. A TGA diagnosis requires no evidence of a head injury or seizures, and the individual cannot have active epilepsy. Reflexes, balance, and coordination will be normal.
The exact cause of TGA is unknown, although experts have identified some possibilities. Abnormalities in blood flow and blood supply or hypoxia could cause the episodes. This is also a likely relationship to migraines. That said, none of these causes apply consistently to all people who have experienced TGA, which means it may have multiple causes.
Some activities have been identified as common triggers, although the risk of a TGA episode following these events is low. Strenuous physical activity, sudden immersion in hot or cold water, mild head trauma, sexual intercourse, medical procedures such as endoscopy or angiography, and psychological or emotional distress could all trigger an episode. TGA has also resulted from excessive alcohol and prescription or illicit drugs.
While high blood pressure and high cholesterol are risk factors for stroke, they do not raise one's risk of TGA. Gender does not seem affect risk either. In fact, there are only two confirmed risk factors. People over age 50 have a higher risk of transient global amnesia, and people with a history of migraines have a significantly increased risk of experiencing TGA.
Since TGA resolves on its own within 24 hours, it generally does not cause any long lasting damage. It does not seem to increase the risk of seizures or stroke, and most cognitive function returns within days. TGA is typically an isolated incident, though there is up to a 26% chance that someone will have reoccurring episodes.
There is no test for a definitive diagnosis of transient global amnesia. Any tests a doctor may run will be to rule out other causes of the event. These tests can include scans such as MRI or CT, an EEG to monitor brain activity, and blood tests. The doctor may also perform neurological exams and psychological evaluations.
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