Subjective cognitive decline: Memory complaints, cognitive awareness, and metacognition

Abstract

Cognitive complaints are common in elderly subjects and are a frequent reason for referral to memory clinics. If the complaints are not associated with objective cognitive impairment, the condition is labelled subjective cognitive decline (SCD). SCD is often considered as a stage antedating objective impairment, and an at-risk condition for subsequent dementia. Recent large-scale studies indicate that a significantly increased risk of clinical progression in subjects with SCD is associated with positivity for Alzheimer's disease (AD) biomarkers, a finding supporting the notion that SCD can be due to different mechanisms not associated with neurodegeneration, including functional cognitive disorders. In this paper we present a selective review of research on the relations among SCD, cognitive awareness, and metacognitive abilities. We propose that longitudinal studies of metacognitive efficiency in SCD may provide useful cues about the risk of progression to dementia and the possible presence of a functional cognitive disorder, with different implications for the management of this prevalent aging-related condition. HIGHLIGHTS: Subjective cognitive decline (SCD), a common cause of referral to memory clinics, can be due to multiple conditions. The predictive value of SCD for progression to Alzheimer's disease (AD) dementia is high in association with AD biomarker positivity. The awareness of cognitive decline is the mechanism responsible for the emergence of SCD and metacognition is the underlying neuropsychological function. The awareness of cognitive decline in clinical patients is usually assessed comparing an informant rating to the patient self-assessment, a method that can be affected by informant bias. While there is strong evidence that awareness starts to decline with the onset of objective cognitive impairment, progressively leading to the anosognosia of AD, the status of metacognitive efficiency in SCD needs to be further investigated. Quantitative, performance-based indexes of metacognitive efficiency may contribute both to the assessment of progression risk and to the management of subjects with functional cognitive disorders.

Keywords: cognitive awareness; memory complaints; metacognition; subjective cognitive decline.

FIGURE 1

Trajectory of objective and subjective cognitive performance. This figure shows the potential dynamic course of normal aging, pathological cognitive changes in the AD continuum, and subjective judgment of cognitive performance. The blue line shows the mean trajectory of normal cognition in aging, while the red line shows the mean trajectory of cognitive decline of a pathological subject; dashed lines indicate the confidence intervals. The distance between the purple line and the red one represents the level of awareness of cognitive decline. AD, Alzheimer's disease; SCD, subjective cognitive decline.

FIGURE 2

Risk factors for dementia and Alzheimer's disease and their corresponding hazard ratio. Modified from Frisoni et al. This figure shows the HR of lifestyle, biological, and genetic risk factors as detailed in the review of Frisoni et al. with the addition of SCD as a risk factor with or without positivity of Alzheimer's disease biomarkers. A, amyloid; APOE, apolipoprotein E; HR, hazard ratio; SCD, subjective cognitive decline; T, tau.

FIGURE 3

Proposed workflow for SCD patients. Modified from Altomare et al., this figure illustrates a possible memory clinic work‐up for SCD individuals. Cognitively unimpaired patients evaluated at memory clinics could benefit from a metamemory assessment before going through a dementia risk assessment, at least before the possible changing clinical scenario associated with the availability of validated blood‐based biomarkers. Based on the limited knowledge available, an initial metamemory screening could identify those at lower risk of developing dementia (functional cognitive disorders) that could benefit from a metacognition training instead of risk reduction protocols. However, there may be individuals who overestimate their decline and are at risk of cognitive decline. Therefore, we recommend monitoring these patients to ensure that their judgment and objective cognition remain stable. ACD, awareness of cognitive decline; SCD, subjective cognitive decline.