Definition of Transient Global Amnesia

Transient global amnesia is a sudden, temporary episode of memory loss that can't be attributed to a more common neurological condition, such as epilepsy, transient ischemic attack, stroke or head injury.

During an episode of transient global amnesia, your recall of recent events simply vanishes, so you can't remember where you are or how you got there. You may also draw a blank when asked to remember things that happened a day, a month or even a year ago. You do remember who you are, and you recognize family members and others you have known for a long time, but that knowledge doesn't make your memory loss any less disturbing.

Transient global amnesia would be even more distressing if it recurred more often or lasted longer than it does. The condition is rare to start with, and among the few who do have one episode, a second episode is uncommon. Also, episodes of transient global amnesia last only six hours, on average — although an episode of any length is frightening to witness or experience.

When an episode of transient global amnesia is over, you remember nothing that happened while your memory was impaired, and you might not recall the hours beforehand. Otherwise, though, your memory is fine.

Transient global amnesia is identified by its main symptom, which is the inability to recall the recent past. Once that symptom is confirmed, ruling out other possible causes of amnesia is important.

Diagnostic Criteria for Transient Global Amnesia

The criteria for a diagnosis of transient global amnesia are:

• Sudden onset of memory loss, verified by a witness
• Retention of personal identity despite memory loss
• Normal cognition (ability to recognize and name familiar objects and follow simple directions, for example)
• Absence of signs indicating damage to a particular area of the brain (limb paralysis, involuntary movement or impaired word recognition, for example)
• Duration of no more than 24 hours
• Gradual return of memory
• No evidence of seizures during the period of amnesia
• No history of active epilepsy or recent head injury

Symptoms of Transient Global Amnesia

Additional signs and symptoms
These signs and symptoms sometimes accompany the chief symptom, memory loss.

• Headache
• Nausea
• Vomiting
• Dizziness
• Chills or flushing
• Fear of dying
• Pins-and-needles sensation
• Cold hands and feet
• Powerful expression of emotion
• Trembling
• Sweating
• Chest or neck pain
• Visual disturbance
• Racing heartbeat

Transient global amnesia is identified by its main symptom, which is the inability to recall the recent past. Once that symptom is confirmed, ruling out other possible causes of amnesia is important.

Diagnostic criteria
The criteria for a diagnosis of transient global amnesia are:

• Sudden onset of memory loss, verified by a witness
• Retention of personal identity despite memory loss
• Normal cognition (ability to recognize and name familiar objects and follow simple directions, for example)
• Absence of signs indicating damage to a particular area of the brain (limb paralysis, involuntary movement or impaired word recognition, for example)
• Duration of no more than 24 hours
• Gradual return of memory
• No evidence of seizures during the period of amnesia
• No history of active epilepsy or recent head injury

Additional signs and symptoms
These signs and symptoms sometimes accompany the chief symptom, memory loss.

• Headache
• Nausea
• Vomiting
• Dizziness
• Chills or flushing
• Fear of dying
• Pins-and-needles sensation
• Cold hands and feet
• Powerful expression of emotion
• Trembling
• Sweating
• Chest or neck pain
• Visual disturbance
• Racing heartbeat

Causes of Transient Global Amnesia

About half of all transient global amnesia episodes start just after a physically or emotionally stressful incident. Among the triggering events commonly reported are:

• Sudden immersion in cold or hot water
• Strenuous physical activity
• Sexual intercourse
• Medical procedures, such as angiography or endoscopy
• Acute emotional distress, as might be provoked by bad news, conflict or overwork

The underlying cause of transient global amnesia is unknown. The incidence of migraine may be higher than can be explained by chance among those affected by transient global amnesia, suggesting that similar processes may be involved in both conditions. Compression of the large veins that empty oxygen-depleted blood from the brain and arms back into the heart may play a role as well. Many of the physical stresses experienced just before an episode of transient global amnesia result in compression of these veins.

Risk Factors

Interestingly, high blood pressure and high cholesterol — which are closely linked to strokes — are not risk factors for transient global amnesia. Your sex doesn't seem to affect your risk, either. Transient global amnesia affects about as many men as it does women.

The clearest risk factors are:

• Age. People between the ages of 56 and 75 have a higher risk of transient global amnesia than do younger or older adults, and the condition very rarely occurs in children.
• History of migraines. If you have migraines, your risk of transient global amnesia is significantly higher than that of someone without migraines. The link appears to be strongest before age 56.

Interestingly, high blood pressure and high cholesterol — which are closely linked to strokes — are not risk factors for transient global amnesia. Your sex doesn't seem to affect your risk, either. Transient global amnesia affects about as many men as it does women.

The clearest risk factors are:

• Age. People between the ages of 56 and 75 have a higher risk of transient global amnesia than do younger or older adults, and the condition very rarely occurs in children.
• History of migraines. If you have migraines, your risk of transient global amnesia is significantly higher than that of someone without migraines. The link appears to be strongest before age 56.

Tests

Diagnosis of transient global amnesia rests on excluding more serious conditions — stroke, seizure or head injury, for example — that can cause the same type of memory loss.

The process begins with a neurological exam, checking your reflexes, muscle tone, muscle strength, sensory function, gait, posture, coordination and balance. Your doctor may also ask questions to test your thinking, judgment and memory. By checking your knowledge of general information — such as the name of the current president — and assessing your ability to recall a random list of words, the doctor can determine the extent of memory loss.

Diagnostic tests

The workup for acute memory loss also includes tests to detect abnormalities in the brain's electrical activity and circulation. The most common of these tests are painless and take less than two hours each.

• Electroencephalogram (EEG). An EEG records the electrical activity of your brain via electrodes affixed to your scalp. People with epilepsy often have changes in their brain waves, even when they're not having a seizure.

  To prepare for an EEG, avoid elaborate hair styling, metallic hair spray or greasy hair dressing. Refrain from caffeine for six hours before the test. The procedure itself is painless and usually lasts about 30 minutes. However, it can take as long as an hour to place the electrodes on your scalp.

• Computerized tomography (CT) scan. Using special X-ray equipment, CT machines obtain images from many different angles and join them together to show cross-sectional images of your brain and skull. CT scans can reveal abnormalities in brain structure, including narrowed, overstretched or broken blood vessels and past strokes.

  To prepare for a CT scan of your head, you should remove such things as earrings, eyeglasses, dentures and hairpins. You may need to have an intravenous (IV) line inserted if your test requires the injection of a contrast material — which makes abnormalities easier to see. During the test, you will lie on a table that slides into the CT machine.

Treatment and Prevention of Transient Global Amnesia

No treatment is needed for transient global amnesia. It's self-limited and has no confirmed after-effects.

Since the cause of transient global amnesia is unknown and the rate of recurrence is low, the effectiveness of preventive measures has been difficult to demonstrate. Some doctors recommend daily aspirin, on the theory that reduced circulation is the cause.

If your episode of transient global amnesia followed a particular activity, such as a strenuous workout or a vigorous swim in a chilly lake, steer clear of that and similar activities.