Subjective cognitive decline as a potential early marker of MCI.

Background: Evidence is mounting that subjective cognitive decline (SCD), the experience of a decline in cognition compared to the previous functioning of a person, could be an early predictor of Alzheimer’s Disease (AD). Until now there is no agreed upon operationalization of SCD and no standardized assessment, which makes it hard to compare results found in different studies. Objective: The objective of current study was to examine whether reporting SCD at baseline predicts conversion to MCI in seven international studies with long-term follow-up (median = 8 years) and to examine within which cognitive domain SCD has the strongest association with conversion to MCI. Methods: From a total of 9135 participants 3943 were included in the analysis. At baseline SCD was assessed by means of different questionnaires per study. Two independent raters scored the questions on five characteristics and after consensus was reached it was decided which SCD questions would be included in current analyses and to which cognitive domain they belonged. Cox regression analyses were used to examine the relationship between SCD and conversion to MCI and to examine the relationship between SCD and conversion to MCI. Results: After controlling for possible effect modifications, which were not found, and risk factors, the total SCD score appeared to be significantly associated with increased risk of converting to MCI (HR = 1.324, 95%-CI = 1.130-1.551). Among the cognitive domains SCD questions concerning memory (HR = 1.380, 95%-CI = 1.168-1.630), attention (HR = 1.557, 95%-CI = 1.146-2.116), and visuospatial abilities (HR = 1.544, 95%-CI = 1.102-2.164) were found to be significantly associated with conversion to MCI. Conclusion: SCD in individuals without MCI or AD at baseline appears to be associated with a higher risk of converting to MCI. Furthermore, SCD questions concerning a change in memory, attention and visuospatial abilities might be especially important in early detection of a possible higher risk of converting to MCI