Possible cause of common dementia found, opening avenues for treatment

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.

Krembil researchers hypothesized that the white matter disease (also called leukoaraiosis) may actually be the result of many tiny unnoticed strokes accumulating over time -- a finding that points to a potentially treatable form of dementia. The research was published today in the journal Annals of Neurology.

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

"We were surprised by the study findings" said Dr. Daniel Mandell, Neuroradiologist, Joint Department of Medical Imaging, Toronto Western Hospital and the principal investigator of the study. "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."

Unlike degenerative types of dementia where there are no treatments, this type, based on vascular disease, is more treatable as it is caused by tiny episodes affecting the blood vessels in the brain over time. It may be possible to prevent or stop this process.

"We don't yet know whether these small strokes are responsible only some or most of the white matter disease seen in older patients," said Dr. Frank Silver, Neurologist and Medical Director, Stroke Program, Krembil Neuroscience Centre and a co-author of the study. "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."

Although more research is needed to further investigate these findings with a larger sample size, if most white matter disease is found to be caused by these tiny strokes, it could eventually lead to interventions to delay its progression in the brain.