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Test for Alzheimerís Disease Predicts Cognitive Decline in Parkinsonís
- Dec 19 2011
A brain imaging method used to detect Alzheimer’s disease can also identify cognitive decline in people with Parkinson’s disease (PD), according to new research published in the November 21, 2011 issue of Brain. Moreover, the test may predict future cognitive impairment in people with Parkinson’s who have no current symptoms of dementia.
Up to 80 percent of people who have had Parkinson’s for longer than 20 years develop dementia. Scientists have noticed similar brain changes in people with dementia associated with Parkinson’s and Alzheimer’s. For example, autopsies indicate that the brains in some people with Parkinson’s undergo atrophy, or shrinking, of the brain in the same regions affected by Alzheimer’s disease.
A team of researchers led by Daniel Weintraub, M.D., at the University of Pennsylvania questioned whether magnetic resonance imaging (MRI) of the brain could detect dementia in Parkinson’s. The team imaged the brains of 84 people with Parkinson’s who had normal cognition, mild cognitive impairment, or dementia. Then they compared the images to brain scans in a database from people with Alzheimer’s. Each person with PD was assigned a SPARE-AD score, which stands for Spatial Pattern of Abnormalities for Recognition of Alzheimer’s disease. The higher the SPARE-AD score, the more similar the person’s pattern of brain atrophy was to those of people with Alzheimer’s.
- Among the 84 people with PD, mean SPARE-AD scores were lowest for those with normal cognition, intermediate for people with mild cognitive impairment, and highest for those with dementia.
- Two years after the brain MRI, the researchers reevaluated the cognitive performance of 59 people from the study who did not have dementia at the time of the MRI. People with relatively high SPARE-AD scores had suffered greater cognitive decline than those with lower scores. Increasing age and postural instability/gait difficulty also predicted long-term cognitive decline.
- Among people with normal cognition at the time of the brain MRI, higher SPARE-AD score and increasing age predicted worse cognitive performance over time.
What Does It Mean?
Currently doctors have very few tools to predict which people with Parkinson’s will eventually develop dementia. This is because we do not fully understand how dementia develops in Parkinson’s.
The findings from Dr. Weintraub and his colleagues strengthen existing evidence that two specific mechanisms contribute to cognitive decline in Parkinson’s. The first is Parkinson’s brain pathology, which results in the formation of protein clumps called Lewy bodies. This pathology may progress from the midbrain/substantia nigra (the part of the brain where movement is controlled) to the cortex (the part of the brain where thoughts form,) leading to dementia. The second is the disease itself. Since the brain pathology of those with Parkinson’s and dementia often show Alzherimer’s-like damage, this suggests that Parkinson’s may be a risk factor for the development of Alzheimer’s or Alzheimer’s related changes in the brain.
This study also provides evidence that similar brain regions undergo neurodegeneration in both PD-related dementia and Alzheimer’s disease. Therefore, some of the brain changes that occur in Alzheimer’s disease may also contribute to cognitive decline in Parkinson’s, the researchers say.
This study shows that this clinical test, largely based on the computer-assisted interpretation of a MRI scan, can theoretically help doctors to better diagnose and treat dementia. However, with all small studies such as this, scientists will need to perform additional investigations with a larger number of participants and longer follow-up periods to verify these results.
Nevertheless, this test, or one similar to it, may one-day help doctors predict dementia before a person with Parkinson’s shows any symptoms.
From the Author
PDF asked Dr. Weintrabub (DW), lead author of this study, about how his findings will impact research and care.
PDF: What might be important for clinicians to "take home" from this research?
DW: That the same regions that undergo neurodegeneration with Alzheimer's disease are also associated with all stages of cognitive decline in Parkinson's disease, reinforcing recent research that memory impairment can be an initial manifestation of cognitive decline and is common in people living with Parkinson's.
What are the potential clinical implications of the findings?
DW: People living with Parkinson's who are not experiencing dementia, but who show particular regions of atrophy or a particular pattern of atrophy using a standard brain MRI, may be at increased risk of long-term cognitive decline and eventual development of dementia.
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Reference: Weintraub D, Dietz N, Duda JE, Wolk DA, Doshi J, Xie SX, Davatzikos C, Clark CM, Siderowf A. Alzheimer“s disease pattern of brain atrophy predicts cognitive decline in Parkinson”s disease. Brain 2011 Nov.
Source Date: Dec 19 2011