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.
Highlights
Over 44 million people worldwide have dementia.[1]
Of these 10 articles, 4 studies considered subjective cognitive decline (SCD) progression to dementia, 3 studies evaluated the conversion of SCD to mild cognitive impairment (MCI) or dementia, and 2 studies analyzed the association between SCD and MCI
The main aim of the review was to compare whether people with SCD are more likely to develop cognitive impairment over time than people without SCD. Cumulative risk of conversion to dementia in the SCD group is 7.23% (95%CI 3.64–12.04)
Summary
Over 44 million people worldwide have dementia.[1] Researchers estimated that there will be 48.1 million people with dementia by 2020 and 90.3 million by 2040.1 Cognitive impairment is a very common cause of disability in the elderly. It is well known that in the most common dementing disorders, e.g. in Alzheimer disease, clinical symptoms develop only after a long period of silent progressive brain damage. It has been established that mild cognitive impairment (MCI) precedes dementia; the significance of subjective cognitive decline (SCD) is still unclear. Recent studies suggest that SCD could be the earliest symptom of the dementing disorder.[2,3,4,5] Reisberg et al, in 1982 and 1986, assumed that subjective complaints constitute the second stage of dementia according to the Global Deterioration Scale and precede objective cognitive decline.[6,7]
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