Factors affecting subjective memory complaints in the AIBL aging study: biomarkers, memory, affect, and age

Background: The prognostic value of subjective memory complaints (SMCs) in the diagnosis of dementia of the Alzheimer's type is unclear. While some studies have found an association between SMCs and cognitive decline, many have found a stronger association with depression, which raises questions about their diagnostic utility. Methods: We examined the cross-sectional association between SMC severity (as measured using the MAC-Q, a brief SMC questionnaire) and affect, memory, and Alzheimer's disease (AD) biomarkers (beta-amyloid deposition and the apolipoprotein E epsilon 4 (APOE epsilon 4) allele) in healthy elderly controls (HC; M = 78.74 years, SD = 6.7) and individuals with mild cognitive impairment (MCI; M = 72.74 years, SD = 8.8). We analyzed a subset of individuals drawn from the Australian Imaging Biomarkers and Lifestyle (AIBL) Study of Aging. Results: SMCs were more severe in MCI patients than in HCs. SMC severity was related to affective variables and the interaction between age and group membership (HC/MCI). Within the HC group, SMC severity was related to affective variables only, while severity correlated only with age in the MCI group. SMCs were not related to cognitive variables or AD biomarkers. Conclusion: SMCs were related to solely by poorer mood (greater depressive and anxious symptomatology) in the cognitively healthy elderly however mean levels were subclinical. This finding argues for the assessment of affective symptomatology in conjunction with cognitive assessment in elderly memory complainers. Future AIBL research will focus on assessing other AD biomarkers, such as brain atrophy and A beta plasma markers, in relation to complaint severity. Once our 36-month follow-up data are collected, we propose to assess whether SMCs can predict future cognitive decline.