Practice effects and amyloid deposition: preliminary data on a method for enriching samples in clinical trials.

Clinical trials in Alzheimer disease are moving toward prevention studies in prodromal individuals with amyloid burden. However, methods are needed to identify individuals expected to be amyloid positive for these studies to be feasible and cost-effective. The current study sought to determine whether short-term practice effects on cognitive tests can identify those with notable uptake on amyloid imaging. Twenty-five, nondemented older adults (15 cognitively intact, 10 with mild cognitive impairment) underwent amyloid imaging through F-flutemetamol and 2 cognitive testing sessions across 1 week to determine practice effects on a visual memory test. Results indicated that, whereas F-flutemetamol uptake showed little association with baseline performance on a visual memory test (r=-0.04, P=0.85), it was significantly correlated with practice effects across 1 week on that same memory measure (r=-0.45, P=0.02), with greater uptake being associated with lower practice effects. The odds ratio of notable F-flutemetamol uptake was 5 times higher in individuals with low practice effects compared with high practice effects. Although these preliminary results need to be replicated in larger samples, short-term practice effects on cognitive tests may provide an affordable screening method to identify individuals who are amyloid positive, which could enrich samples for preventative clinical trials in Alzheimer disease.