A three-year study involving 152 adults aged 50 and older, of whom 52 had been recently diagnosed with mild cognitive impairment and 31 were diagnosed with Alzheimer's disease, has found that those with mild or no cognitive impairment who initially had amyloid-beta plaques showed greater cognitive decline than those whose brain scans were negative for plaques. Moreover, 35% of plaque-positive participants who started with MCI progressed to Alzheimer's, compared to 10% without plaque, and they were more than twice as likely to be started on cognitive-enhancing medication.
The fact that 90% of those with MCI but no plaque didn’t progress to Alzheimer's (within the three-year period) points to the value of using PET imaging to identify patients unlikely to decline, who can be reassured accordingly. The finding also points to the importance of plaque buildup in cognitive decline.
 Florbetapir F 18 amyloid PET and 36-month cognitive decline:a prospective multicenter study. Molecular Psychiatry [Internet]. 2014 . Available from: http://www.nature.com/mp/journal/vaop/ncurrent/abs/mp20149a.html