Among patients with mild or no cognitive impairment, PET imaging using florbetapir, which binds to amyloid plaques in the brain, has been shown to detect early evidence of Alzheimer’s disease (AD) that may predict future decline, according to findings published online July 11 in Neurology.
"Even at a short follow-up of 18 months we can see how the presence of amyloid plaques affects cognitive function," P. Murali Doraiswamy, MD, professor of psychiatry at Duke University in Durham, N.C., said in a release.
The research conducted by Doraiswamy and colleagues expands on smaller studies which demonstrated that early detection of amyloid plaques could be a predictive tool and aid treatment decisions for AD patients.
A total of 151 people who had enrolled in a multi-center test of florbetapir were recruited to participate in the study. Subjects had various levels of cognitive function, with 51 recently diagnosed with mild cognitive impairment (MCI), 31 with clinically diagnosed AD dementia and 69 cognitively normal adults serving as the control group. All underwent florbetapir PET imaging, with the resulting images scored for beta-amyloid aggregation.
At baseline, 37 percent of subjects with MCI, 68 percent of subjects with AD dementia and 14 percent of cognitively normal subjects had amyloid-positive PET scans, reported the authors.
When subjects were reassessed at 18 and 36 months to evaluate changes in cognition and diagnostic status, cognitively normal adults and those with MCI who had evidence of plaque on the initial PET scan had greater clinical worsening on the AD Assessment Scale—Cognitive subscale and Clinical Dementia Rating-sum of boxes score. Amyloid-positive scans were also associated with greater declines in memory, Digit Symbol Substitution and Mini-Mental State Examination.
The findings suggest that amyloid PET could have predictive value for MCI progressing to AD dementia, according to Doraiswamy and colleagues. In patients with MCI, higher baseline standardized uptake value ratios correlated with greater declines in cognitive ability at follow-up. Of plaque-positive MCI patients, 29 percent developed AD, compared with 10 percent who had no plaque at baseline.
“In very mildly impaired patients with MCI, where conversion to dementia is a relatively distant outcome, the ability to assess risk of cognitive decline (e.g., from mild to more severe MCI) could be clinically useful for making ongoing care recommendations,” wrote the authors.
Additional research will be needed to confirm the results, according to the authors. Final, 36-month data from the study has been completed and will be presented at the Alzheimer’s Association International Conference in Vancouver, Canada.
These findings support the potential utility of florbetapir PET as a predictive biomarker of cognitive decline in at-risk subjects. "While additional longer-term confirmatory studies are necessary, this study also provides preliminary support to the proposed research concepts of preclinical AD (in cognitively healthy subjects) and MCI of the Alzheimer type,” summed the authors.
To read more about the first U.S. sites to provide florbetapir PET imaging, which was FDA approved in April, click here.