Clinical definition, biological characterization, and detection guidelines of subjective cognitive decline due to Alzheimer's disease and related dementia: A position paper from ISTAART SCD PIA.

Subjective cognitive decline (SCD)-self-perceived cognitive worsening without objective deficits-has emerged as a clinically meaningful, potential early manifestation of Alzheimer's disease (AD). Positioned at the intersection of normal aging, neuropsychiatric symptoms, and preclinical neurodegeneration, SCD offers a unique window for early detection and intervention. However, detection heterogeneity, variable prognostic trajectories, and limited equity in assessment hinder its full clinical utility. This position paper synthesizes current evidence on SCD's diagnostic complexity, neurobiological underpinnings, and modifiable influences. We highlight the need for harmonized assessment frameworks, scalable digital tools, inclusive research, and ethically grounded biomarker disclosure practices. Importantly, we advocate for personalized, (non-)pharmacological interventions targeting this early phase. By refining the conceptualization and operationalization of SCD, we can better identify individuals at heightened AD risk and deliver timely, equitable, and meaningful prevention strategies. SCD represents a pivotal inflection point in the dementia continuum-and a call to shift toward proactive brain health. HIGHLIGHTS: Subjective cognitive decline (SCD) may signal early-stage Alzheimer's despite normal test performance. Diagnostic heterogeneity limits current clinical and research utility. Biomarkers and digital tools could enhance risk stratification in SCD. Mental health and social context shape symptom reporting and outcomes. SCD offers a window for tailored (non-drug) preventive interventions.