Older people who are leading active, healthy lifestyles often have silent vascular disease that can be seen on brain scans that affect their ability to think, according to a new study published online Nov. 8 in the Archives of Neurology.
Over 5 million elderly people in the United States have Alzheimer's disease. Cardiovascular disease, including hypertension, high cholesterol and atherosclerosis, is also common in the elderly, and causes "white matter hyperintensities," regions of damaged brain tissue that look like white-hot areas on MRI scans. The researchers sought to better understand the relationship between white matter hyperintensities and the extent to which they precede, coincide with or follow short-term changes in cognitive functioning.
The study findings are based on data from participants in the Alzheimer's Disease Neuroimaging Initiative. The initiative tracks individuals who are normal, those who have mild cognitive impairment (MCI) and people with Alzheimer's disease using MRI, PET imaging and laboratory and cognitive testing to track changes in their cognitive status.
For the study, 804 participants ages 55 to 90 were recruited from more than 50 research sites throughout the United States and Canada. Some 200 participants were cognitively normal individuals who were followed for three years. Approximately 400 people with mild cognitive impairment were followed for three years. Two hundred people with Alzheimer's disease were followed for two years. Potential participants with serious brain anomalies, such as brain tumors or prior surgery, were excluded from the study.
All of the participants' baseline cognitive functioning was established using clinical diagnostic evaluation, including the Mini Mental State Exam and the Alzheimer's Disease Assessment Scale-Cognitive Subscale. Criteria for the normal group included no evidence of depression, mild cognitive impairment or dementia. Individuals were included in the MCI category if they had a subjective memory complaint or objective memory loss, among other measures. Participants with Alzheimer's disease met nationally accepted criteria for probable Alzheimer's disease.
Participants whose white matter hyperintensities were significantly above average at the beginning of the study lost more points each year in cognitive testing than those whose white matter hyperintensities were average at baseline. The presence of white matter hyperintensities and MCI or Alzheimer's disease together added up to even faster and steeper cognitive decline. In addition, participants who were older at baseline saw faster declines over time in their Mini Mental State Exam scores. The researchers found that, at the outset of the study, the extent of white matter hyperintensities was associated with greater subsequent declines in global cognition over a one-year period.
"There's a big group of people who have not had major cardiovascular events such as heart attacks. But we see signs that even milder vascular-related insults can contribute to loss of cognitive functioning," said Owen Carmichael, PhD, assistant professor in the department of neurology in the School of Medicine at University of California, Davis.
"This study shows that silent vascular disease is really common as we get older and it influences our thinking abilities,"said Charles DeCarli, MD, professor of neurology in the School of Medicine and director of the University of California, Davis Alzheimer's Disease Center. "We're beginning to realize that vascular disease plays a major role in Alzheimer's disease — they go together."