Approximately 50 per cent of older individuals have evident white matter damage on their medical imaging scans. For most patients, these changes are harmless but when this damage is severe, it can cause impairment. Previous studies have already established that the more white matter disease there is in the brain, the more likely patients are to have symptoms of dementia such as cognitive impairment or changes in behaviour. What was not understood is why this white matter disease develops - the traditional assumption was that it might be the result of the natural aging process.
The researchers conducted an intensive study to observe the development of this white matter disease over a short period of time, rather than on an annual basis - the interval at which previous studies have performed repeat brain imaging. The study involved 5 patients with white matter disease undergoing detailed MRI scanning of their brains every week for 16 consecutive weeks. The weekly MRI scans revealed new tiny spots arising in the brain's white matter that were, based on their MRI appearance, characteristic of small new strokes (cerebral infarcts). The lesions had no symptoms but, with time, came to resemble the existing white matter disease in the subjects' brains. In the study's random sampling, the majority of subjects had this phenomenon: Tiny strokes occurring without symptoms, and developing into the kind of white matter disease that causes dementia.
"The findings suggest that the tiny, silent strokes are likely much more common than physicians previously appreciated, and these strokes are likely a cause of the age-related white matter disease that can lead to dementia. We don't yet know whether these small strokes are responsible only some or most of the white matter disease seen in older patients. But in those where it is the cause, the detection of white matter disease on brain imaging should trigger physicians to treat patients aggressively when managing stroke risk factors such as high blood pressure, diabetes, high cholesterol, cigarette smoking and lack of exercise not only to prevent further strokes, but also to reduce the development of cognitive impairment over time."