Subjective cognitive decline as a predictor of future cognitive decline: a systematic review

Abstract

ABSTRACT. Over 44 million people suffer from dementia around the world. Researchers estimated that there will be 48.1 million people with dementia by 2020 and 90.3 million by 2040. In addition to dementia, mild cognitive impairment (MCI) and subjective cognitive decline (SCD) relate to cognitive impairment. It has been established that MCI precedes dementia, however the significance of SCD is still unclear. Recent studies suggest that SCD could be a risk factor for objective cognitive impairment. SCD is defined as а self-estimated decline in cognitive capacity in comparison to an individual’s previous level of functioning, which cannot be determined by neuropsychological tests. Objectives: To perform a systematic review of prospective longitudinal cohort studies that assessed the risk of MCI and dementia among people with SCD. Methods: A search was carried out for all available peer-reviewed articles in English related to SCD in PubMed and PsychINFO databases from database initiation through January 2020. The keywords used for the search were ‘subjective cognitive (or memory) impairment (or decline or complaints)’. Three authors separately determined the inclusion or exclusion of all articles retrieved for full-text evaluation. Results: The chance of progression to dementia in the SCD group was 2.17 (95% confidence interval [95%CI] 1.53‒3.07; p<0.05) compared to normal aging. Furthermore, the SCD group was 2.15 times more likely to progress to MCI than the group without SCD (95%CI 1.39‒3.30; p=0.005). Conclusions: SCD might precede cognitive impairment, however, more detailed longitudinal studies should be conducted.

tDCS-Induced Memory Reconsolidation Effects and Its Associations With Structural and Functional MRI Substrates in Subjective Cognitive Decline

“…Within this context, the condition termed subjective cognitive decline (SCD) has been defined to refer to individuals over 60 years of age, without evidence of objective cognitive impairment on formal testing, but who report self-perception of worsening cognitive capacity ( Jessen et al, 2014 ). SCD is commonly present in preclinical stages of neurodegenerative diseases ( Parfenov et al, 2020 ), and is considered a risk factor for developing amnestic mild cognitive impairment (MCI) and subsequently dementia due to Alzheimer’s Disease (AD; Abdulrab and Heun, 2008 ; Reisberg and Gauthier, 2008 ).…”

What do we know about the risks of developing dementia after traumatic brain injury?

“…Mild cognitive impairment (MCI) is often a prodromal stage between normal aging and dementia, constituting a period of objective cognitive difficulties but only mildly affected functional abilities. Not all those diagnosed with MCI will progress to dementia however 19 .…”

The Effect of CAG Repeats within the Non-Pathological Range in the HTT Gene on Cognitive Functions in Patients with Subjective Cognitive Decline and Mild Cognitive Impairment

“…Subjective cognitive decline (SCD) is the self-experienced decline in cognitive capacity with normal performance on standardized cognitive tests [1]. Individuals with SCD are twice as likely to develop dementia as individuals without [2]. Mild cognitive impairment (MCI) describes subjects with objective cognitive impairment without an impact on instrumental activities of daily living [3], and it is considered a transitional state between the normal cognitive state and dementia.…”