DEAR DOCTOR: Can you shed some light on transient global amnesia? I was diagnosed with this five years ago (I'm now 71) after my family noticed that I couldn't recall common facts. I had no physical ailment or injury prior to this, and I'm told that the recurrence rate is 1 percent.
DEAR READER: Transient global amnesia is, as the name describes, a short-lived inability to retain new memories. Because the episodes are so sudden, they can be disorienting to all involved. Afflicted people often repeatedly ask questions about the date, their location or their reason for being there. They can temporarily lose memories from a few hours before the event to, more rarely, up to a year before the event.
Note that such episodes do not affect a person's ability to perform complex tasks such as driving, cooking, lecturing and playing a musical instrument. Nor do the events interfere with self-awareness.
The episodes last, on average, about six hours, but can be as short as one hour or as long as 10 hours. Afterward, a person does not remember anything that transpired during the episode and may even lose some memories formed just before the incident. Although the episodes can be preceded by an acute emotional event, physical activity, or exposure to cold or heat, doctors don't really know what causes such amnesia.
MRIs have shown that the events affect the memory centers of the brain in the temporal lobe and in the hippocampus. Like the symptoms, however, the resulting lesions that develop in these areas are not permanent. Some brain experts suspect that blood flow restriction may be a trigger, but the evidence for this is thin. Another hypothesis, which has more merit, is that a backflow of venous blood is the catalyst; such flows are more likely to affect the aforementioned parts of the brain.
One strong risk factor is psychogenic stress -- in other words, a psychiatric condition that produces a physical response. A 2005 study found that people with a history of psychiatric disease or alcohol abuse had three times the likelihood of experiencing transient global amnesia.
The condition typically occurs in people ages 50 to 80 and is diagnosed in one in every 3,500 people over 50 each year in the United States. The peak incidence occurs in those 60 to 65. Men and women are equally affected. Because the symptoms can resemble those of a stroke or a transient ischemic attack, many people mistake the condition for a stroke or TIA. Unlike those conditions, however, transient global amnesia doesn't have a vascular cause, and people who experience it have the same incidence of stroke as the general population. Nonetheless, because of the similarity in symptoms, immediate medical attention is needed to rule out more serious causes.
You mention a 1 percent recurrence rate, but studies have shown the rate to be about 5 percent. This is still very low.
This sudden loss of memory must have been unnerving for you. Please take some comfort in the fact that it's unlikely to happen again.
(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)
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