Subjective and objective cognitive decline at the pre-dementia stage of Alzheimer's disease.

Research on Alzheimer's disease (AD) dementia prediction has moved from the mild cognitive impairment stage to the preclinical stage of AD. This has also extended the focus from the early clinical sign of cognitive impairment measured with neuropsychological tests to the purely subjective report of cognitive decline (SCD) in unimpaired elderly individuals. Epidemiological studies have shown that both objective impairment and SCD are independently predictive of AD dementia. Both are also associated with an increased likelihood of biomarker or neuroimaging evidence of AD. However, the relationship of objective and subjective cognitive performance along the axis of AD development and their role at different stages in prediction of AD dementia is not well explored. Refined knowledge about strengths and weaknesses of both aspects at different pre-dementia disease stages will be beneficial for dementia prediction. Both concepts and their interaction are introduced in this article.