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Sunday, September 24, 2023
Dr. Brown: The curious case of short-lasting memory loss
Dr. William Brown. File Photo

Forgetting the names of people, where you placed the car keys and the occasional appointment are common much beyond the age of 80.

We’re all guilty as charged and most of the time, those embarrassments and inconveniences are just that – not tell-tale signs of impending dementia, a stroke or anything else worrisome.

Sometimes memory loss is acute and lasts several days. That’s what happened to my father-in-law, Bob, when the family was vacationing in Barbados.

One evening at dinner, his speech became slurred, his mouth sagged on the left and his left arm and leg became mildly weak, none of which he was aware of until I pointed out the weakness to him. This all cleared up within a few minutes, only to reoccur an hour or so later.

We took him to the local hospital – not very impressive in those days – and the decision was made for me to get him on the first flight back to Toronto and thence University Hospital in London the following morning.

On the return flight to Toronto, as we climbed to cruising altitude, the weakness reoccurred only to, fortunately, go away with nasal oxygen.

Once in Toronto, it was obvious Bob could not remember the several-hour flight from Barbados to Toronto, or rolling forward, the subsequent flight to London Ontario, admission to University Hospital and most of the following day.

Otherwise, Bob’s neurological examination was normal – except he was unable to remember what was said to him or even that we had been with him in his room a minute or so earlier, although longer-term memories were intact.

Imaging studies revealed a small ischemic lesion involving the right dorsal medial nucleus of the thalamus, which is part of the memory circuit.

Such discrete, localized lesions affecting the retention and recall of memory are rare – rare enough that my colleague who looked after Bob at University Hospital reported his case, complete with an MRI picture of the small thalamic lesion.

Occasionally, people in mid-age or later develop acute memory loss associated with no symptoms – other than a several-hour period in which they are completely unable to recall anything during this timeframe, nor anything several hours before the first symptoms.

Characteristically, these patients compulsively and repeatedly ask questions such as, “What’s going on?” and “How did I get here?” There are no other neurological signs or symptoms to suggest migraine, stroke or epilepsy or any other specific disorders as the cause.

In that sense, the disorder is a clinical syndrome of exclusion.

The disorder was first described in 1958 by Miller Fisher, a Canadian by birth, and Raymond Adams from Harvard University and the Massachusetts General Hospital. They gave it the name “transient global amnesia.”

Patients invariably recover with no deficits, although occasionally recurrences happen which are equally benign. Despite several extensive clinical studies, no specific cause has been identified, although the features of the memory loss point to something happening somewhere along the memory circuit from the hippocampus to the thalamus.

Episodes may be triggered by some significant event such as extreme exertion, news of a death, sexual assault, severe pain or, according to a series completed by the Mayo Clinic in Minnesota’s farm country, “strenuous farm work.”

A migraine is sometimes associated with a cycle of spreading excitation followed by depression involving the neocortex, often involving the visual area.

The excitation period is marked by bright lights, dots or zigzags in the related visual fields and is usually followed by a period of neocortical depression in the same region of the visual field marked by temporary blindness.

Whether a similar physiological process might involve the hippocampus and/or thalamus in transient global amnesia syndrome is speculation and a reminder that 65 years later, the cause of transient global amnesia remains a mystery – fortunately, a benign one.

Remember, the syndrome is very specific and deviations from the usual pattern might well be cause for serious concern.

To return to my father-in-law – none of us were aware that Bob had a two-year history of angina associated with brisk walking. That history suggested Bob might have had a “silent” heart attack in the days or few weeks before the transient ischemic attacks and later stroke.

If so, the latter might have been related to emboli from a previously-infarcted region of his heart. Evidence of such a series of events was found in subsequent cardiac studies.

Bob later confessed he had been reluctant to tell anyone about the angina. Sound familiar to some males?

Dr. William Brown is a professor of neurology at McMaster University and co-founder of the InfoHealth series at the Niagara-on-the-Lake Public Library.  

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