Subjective Cognitive Decline as a Preclinical Marker of Dementia: A Theoretical Review and Conceptual Framework of Longitudinal Studies in Older Adults

Subjective cognitive decline (SCD) refers to a persistent self-perception of deteriorating cognitive function, particularly in memory, despite normal performance on standardized neuropsychological assessments. Increasing evidence supports its role as a potential preclinical marker of the Alzheimer's disease (AD) continuum. In recent years, the field has witnessed substantial growth, prompting the development of novel research frameworks and methodological approaches. This theoretical study synthesizes recent advances and key findings from longitudinal studies, which offer critical insights into the temporal relationship between SCD and progression to clinically defined stages of cognitive impairment. The literature consistently reports associations between SCD and subtle declines in objective cognitive performance, as well as the influence of sociodemographic and psychosocial factors, including differences related to sex and ethnicity. Additionally, emerging data link SCD with alterations in neurobiological biomarkers assessed through neuroimaging and fluid-based analyses, reinforcing its relevance as an early indicator of pathological aging. Based on this body of evidence, a preliminary comprehensive evaluation framework for clinical practice is proposed to improve early detection. Together, these findings underscore the need for standardized diagnostic criteria and integrative models that encompass the clinical, biological, cognitive, and psychosocial domains to enhance the predictive and diagnostic value of SCD in the context of neurodegenerative disease.