Multiple recent unsuccessful late-stage drug trials in people with mild to moderate Alzheimer's disease have lead some in the field to believe that treating people when dementia symptoms are apparent is too late in the disease process and that we must move detection and intervention earlier in order to be effective. Some experts believe that the best time to treat individuals with Alzheimer's is when cognitive performance is still normal but there is evidence of Alzheimer's changes in the brain. This is described as preclinical (or presymptomatic) Alzheimer's in new diagnostic criteria published by the U.S. National Institute on Aging and the Alzheimer's Association.

To identify these individuals earlier, researchers tested whether performance on tests of memory and thinking in cognitively normal individuals was related to preclinical Alzheimer's disease.  They presented their results at the 2013 Alzheimer's Association International Conference.

Dorene M. Rentz, Psy.D., associate professor of Neurology at Harvard Medical School and a neuropsychologist in the Departments of Neurology at Massachusetts General Hospital and Brigham and Women's Hospital, Boston, and colleagues tested whether performance on tests of memory and thinking in cognitively normal individuals was related to preclinical Alzheimer's disease.

The group studied 129 normal older adults, age 65 to 85, with cognitive tests and two PET brain scans: one that measures how the brain uses glucose (FDG metabolism) and another scan that measures the amount of brain amyloid plaques (PiB deposition). 

The researchers found that people in the study with worse memory performance had higher PiB deposition and lower FDG metabolism in regions of the brain that are commonly affected in Alzheimer's. In contrast, individuals who performed worse on non-memory thinking tests had lower FDG metabolism but a normal PiB scan.

They also found that more highly educated individuals in the study performed normally on tests of memory despite lower FDG metabolism and higher PiB retention. "This may mean that education has a protective effect on cognitive performance in the early stages of preclinical Alzheimer's," Rentz said.

"Overall, our findings suggest that poor memory performance with both FDG metabolism and higher PiB deposition may help identify people who are at high risk for progression to Alzheimer's disease dementia," Rentz said.