Elizabeth A. Reid, MD A Slip of Memory S
EARCH the Internet for drugs that cause memory problems, and you will quickly become familiar with a fascinating syndrome called tran- sient
global amnesia (TGA).
Some people, including astro- naut-physician Dr. Duane Grave- line, who has twice experienced TGA, believe that the syndrome is related to cholesterol-lowering drugs known as statins. Dr. Graveline has recounted how his instances of TGA took place six weeks after he started taking a statin during his yearly astronaut physical, which was conducted at Johnson Space Center. TGA is not officially listed as an ad- verse effect associated with statins, but with twelve million Americans now using these prod- ucts, recognition of the possibil- ity of this side effect by patients and doctors is important. Beyond the tightly controlled world of premarket drug approval studies, unexpected symptoms need to be noted.
TGA is a short-lived problem
and is usually over in less than twenty-four hours. It involves all aspects of new memory forma- tion, which means that nothing gets recorded in the brain during the event. When it is over, the affected person cannot recall what happened to him, so our understanding of the event must come from those who observed it as it took place. An individual
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Diagnostic Criteria for Transient Global Amnesia • A witness must be present to describe what happened.
• The patient must be unable to form new memories of any kind (anterograde amnesia).
• The patient must have full knowledge of his identity and an unclouded state of consciousness.
• No other neurological symptoms or signs are present. • No signs of a seizure are detected.
• The patient has no history of seizures within the last two years or of recent head injury.
• The patient is back to normal within twenty-four hours.
experiencing TGA appears to lose access to a few hours, days, or even years of past memory, but usually not to memories about himself. He looks around but can- not identify why he is where he is, and depending on how much access to the past he has lost, his current situation might totally mystify him. With great urgency he questions the people around him— “What am I doing here?” “How did I get here?” “What’s going on?” He understands what he is told and can hold on to the information he is given for about thirty seconds. But his ability to store that information has gone offline. He forgets. He asks again, and again, and again, with obvi- ous anxiety. All his other mental capacities work well. He can speak, read, write—even drive and problem solve. Except for his anxiety, he seems to be the
same person as always. Then the confusion ebbs. His memory formation starts up, and his past memories return, gradually and in
chronological order. Once
again, he is tethered to time and place, but he will never remem- ber what went on while he was cut loose. For a while, he might complain of a slight headache.
Occurrence and Diagnosis The first descriptions of these
odd symptoms appeared in an obscure medical journal in 1956. More cases then came to light, and by the early 1990s there were a few studies that suggested that TGA occurs in about ten out of every one hundred thousand people. In the most susceptible age-group, those fifty to eighty years old, the rate goes up to twenty-five to thirty-two out of ev- ery one hundred thousand
people. Far from being harbin- gers of impending stroke or evi- dence of seizures, these short episodes seem to have no corre- lation with any problems other than a history of migraine. They also leave no complications in their wake, but they do recur in somewhere between 5 and 25 percent of cases, with one par- ticular patient having more than a dozen recurrences. No definite cause has ever been found, though many physicians have noted that, fairly often, physically or emotionally strenuous events immediately precede the onset of a TGA episode.
In 1990, criteria for the diag- nosis of TGA were published (see sidebar), and when a diagnosis of TGA strictly adheres to these criteria, it is almost always safe to predict that there is no under- lying neurological or vascular problem. Nevertheless, when a patient appears in an emergency room with TGA symptoms, good practice still requires a comput- erized tomography (CT) scan or magnetic resonance imaging (MRI) and an electroencephalo- gram (EEG) to rule out the re- mote possibility of an underlying tumor, hemorrhage, or seizure disorder. Very rarely, underlying brain problems, like tumors in- volving the deep middle and fron- tal areas of the brain where memory formation takes place, (Continued on page 78)
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