Longitudinal Trajectories of Episodic Memory in Older Adults in Preclinical stages depending on whether they remain Stable or Progress to Mild Cognitive Impairment: Evidence from the CompAS and CIMA-Q cohorts

Subjective Cognitive Decline (SCD) refers to self-perceived decline in the absence of objective cognitive impairment, but whether longitudinal decline differentiates stable and progressing Cognitively Unimpaired (CU) and SCD individuals remains unclear. We aimed to analyse longitudinal differences in memory trends in stable and progressing CU and SCD participants to Mild Cognitive Impairment (MCI) from two methodologically similar cohorts, Compostela Aging Study (CompAS) and Consortium for the Early Identification of Alzheimer's Disease (CIMA-Q). 216 participants (67.09 ± 8.29 years) without objective cognitive impairment were classified into four groups considering baseline diagnosis and progression at two follow-ups: CU-S (CU who remained stable), SCD-S (SCD who remained stable), CU-P (CU who progressed to SCD/MCI), and SCD-P (SCD who progressed to MCI). Memory was assessed using immediate, short-, and long-delay free recall measures. Longitudinal memory trends were evaluated considering time as within-subject factor, group as between-subject factor, and schooling, age, and comorbidity as covariates. Longitudinal episodic memory declines were larger in CU-P in long-delay and, particularly, in SCD-P in all three memory measures compared to stables. For immediate memory, slope decline was similar in SCD-P, but the group effect also indicated lower performance in SCD-P at baseline. Long-delay measure was able to differentiate longitudinal memory decline between SCD-P and CU-P groups. Our results suggest that longitudinal change in delay measures is concurrent with diagnostic change in at-risk SCD participants. Immediate memory might be more discriminative as early risk marker, but not intense enough to detect worsening in at-risk SCD or differentiate it from at-risk CU group.