Researchers have found further troubling evidence that cognitive damage from white matter disease is more widespread than first thought. A comprehensive meta-analysis of twenty seven published studies comparing healthy older adults to those who have cognitive impairment due to white matter disease has revealed that the disease can sabotage several cognitive areas.
Led by the Rotman Research Institute at Baycrest Health Sciences in Toronto, in collaboration with the University of Toronto Scarborough, the findings are published online today in the British Journal of Neuropsychology, ahead of print publication.
"A central characteristic of white matter disease is impairment of executive functions and speed of thinking, but there's long been suspicion in the scientific and clinical communities that the disease impairs a broader range of cognitive areas," said the study's lead author, Brandon P. Vasquez, a PhD candidate with Baycrest's Rotman Research Institute and the Department of Psychology at the University of Toronto.
"Our findings add to a growing body of evidence that white matter disease is a discreet saboteur in the brain, impacting a large number of cognitive functions."
Unlike Alzheimer's disease which shrinks the hippocampus causing progressive memory loss, white matter disease is a more diffuse mind-robbing condition that targets small blood vessels deep within the brain's white matter. The disease hardens the tiny arteries, gradually restricting nutrients to white matter -- the connections between brain regions involved in executive abilities such as planning, organizing, problem-solving, and attention. The disease increases a person's risk of having a stroke, or even developing a full-blown dementia such as vascular dementia or Alzheimer's disease.
Vasquez and University of Toronto Scarborough research colleague, Dr. Konstantine Zakzanis, reviewed the cognitive performance scores of 2,544 individuals across twenty seven published studies. Of this total group of adults, 794 had a clinical diagnosis of cognitive impairment due to a vascular cause (white matter disease) but not serious enough to compromise their ability to function in their daily lives (no dementia). The other 1,750 were healthy controls.
Compared to healthy subjects, the patients with vascular cognitive impairment showed significant deficits in all eight cognitive domains examined, including executive functioning, thinking speed, general functioning, language, immediate memory, delayed memory, working memory and visuo-spatial construction. Thinking speed showed the greatest impairment, followed by immediate and delayed memory, while working memory and visuo-spatial abilities were the least affected.
It is estimated that 5 per cent of Canadian adults aged 65-and-older have vascular cognitive impairment (Rockwood et al. 2000), with white matter disease likely contributing in the majority of cases. The disease is thought to be linked to hypertension, high cholesterol, poorly-managed diabetes, an unhealthy diet, lack of exercise, and smoking.
"White matter disease is a covert operator. It can slowly strangle the brain's connecting pathways over time," said Vasquez. "Many people may have white matter lesions and not even know that they do or that they should seek clinical testing for a diagnosis. This can occur because individuals may be unaware of incremental changes to cognition, or because they ignore mild changes that they attribute to the aging process. This makes it difficult to nail down a more precise prevalence rate in the Canadian population."
The good news is that white matter damage can be minimized by adopting the same healthy lifestyle habits that reduce the risk of heart attack and stroke. These include eating a low fat, healthy diet, regular exercise, managing blood pressure and cholesterol levels, and blood-sugar levels if you're a diabetic, and not smoking.
Rotman Research Institute senior scientist Dr. Nicole Anderson was a senior advisor on the paper. The study was funded by the Natural Sciences and Engineering Research Council of Canada.
White matter disease is responsible for about a fifth of all strokes worldwide (Sudlow, 1997), more than doubles the future risk of stroke (Debette 2010, Vermeer, 2007), and is a contributing factor in up to 45% of dementias (Gorelick, 2011).
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