Transient Global Amnesia

Transient Global Amnesia (TGA) is a rare disorder of unknown cause. It is seen mainly in patients between the ages of 55 and 75. It commonly follows a stressful event, but at least 50% of episodes occur with no previous stressor. The sole feature of the disorder is the sudden loss of antegrade memory.

The patient is oriented to person but can retain no new information for more than a few seconds. Memory of past events is usually impaired as well. Since the disorder is rare, physicians who have never seen a patient with it will suspect a stroke as the cause of the amnesia. But a physical exam performed during an episode will clearly differentiate TGA from a CVA. Here is a typical case:

A 67 year old woman was brought to the emergency room by her husband. A teacher, she had left her school and was in her car when she became aware that something was very wrong. She was able to phone her husband and drive home. He returned home and found her confused. She did not remember calling him nor did she remember driving home. He brought her to the ER. In the ER she was oriented to person, but could not remember where she was. She did not know that her mother was dead (she had died 10 years ago). She could not remember anything she was told and kept repeatedly asking the same questions. She did not know the year. Her blood pressure was 190/105  Her neurological examination was entirely normal except for the memory loss. CT and MRI of the head were normal. She was admitted to the hospital. Her memory started to return six hours after the onset of her problem and was completely normal the next morning. Her blood pressure (which had been normal before this episode) was controlled with atenolol and subsequently has been controlled with 10 mg of lisinopril twice a day. She is now asymptomatic. She has no memory of the period of amnesia.

After the patient’s memory returned she remembered taking 30 mg of pseudoephedrine on the morning of the day she suffered the episode of TGA. The role of this drug in precipitating the episode and its accompanying hypertension is unclear.

The diagnosis of this syndrome requires the following:
1. The attack be witnessed
2. There be loss of recent memory (antegrade amnesia)
3. No history of head trauma or epilepsy
4. No clouding of consciousness
5. Neurological examination is normal except for memory loss
6. The attack resolves in less than 24 hours

The incidence of this disorder may be as high as 235 per million in patients over 50 years of age. It may be more common in people with migraines. Though there has been speculation about disruption of blood flow to some parts of the brain, the cause of the syndrome is unknown. What’s important is that the correct diagnosis be made and that patients and especially their families be reassured about its benign prognosis. Repeat episodes are unlikely. The range of recurrence is said to be 3 to 25 %. More details about this disorder can be found at the sites below.

http://www.med.ucla.edu/modules/wfsection/article.php?articleid=38
http://emedicine.medscape.com/article/1160964-overview
http://www.mayoclinic.com/health/transient-global-amnesia/DS01022

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