Subtle memory decline over 12 months in mild cognitive impairment

OBJECTIVE: Screening of normal older persons for progressive memory decline is a worthwhile strategy in the pursuit of the earliest possible stages of pre-clinical Alzheimer's disease (AD) or mild cognitive impairment (MCI). Reliable tests are needed to both detect MCI and measure the natural history of decline over months rather than years. We aimed to detect memory decline over 1 year in a group of older individuals with well-characterised amnestic MCI. METHODS: The continuous learning task (CLT) from the CogState test battery was administered 8 times in 12 months to 15 individuals with MCI and 35 controls matched for age, education, IQ and gender. All subjects were recruited from an ongoing aging study. The rate of change in CLT performance over the year was compared between groups and also compared to that detected with a word list learning task and a computerised paired associate learning task. RESULTS: At baseline, memory performance in the amnestic MCI group was significantly worse than controls on all memory tests. However, at 12 months the magnitude of the difference between the groups had increased significantly on the CLT due to decline in memory accuracy in the MCI group. No decline over 12 months was detectable on the routine memory tests. CONCLUSIONS: Subtle memory decline is detectable in amnestic MCI using reliable and sensitive tests of memory. Such measures may assist in the early identification of AD and also in trials of putative disease-modifying therapies to be conducted over as little as 12 months.