Mild cognitive impairment: narrative review of taxonomies and systematic review of their prediction of incident Alzheimer's disease dementia

Abstract

Early detection of Alzheimer's disease is vital for developing novel treatments. Attempts to identify the intermediate state between normal cognition and dementia have evolved over the past 50 years. Current taxonomies of mild cognitive impairment (MCI) may be criticised for their imprecise operationalisation. With the advent of biomarkers such as amyloid-beta positron emission tomography imaging in established Alzheimer's disease, much research has focused on establishing which factors predict progression from MCI to Alzheimer's disease dementia. In this review, we discuss the historical context of MCI before reviewing the literature of MCI subtypes and their risk of progression to Alzheimer's disease dementia. Finally, we summarise the literature and discuss limitations and weaknesses of how the construct is operationalised and implemented, before offering suggestions for development of the concept of MCI. We conclude that MCI must be empirically defined for the sake of its predictive validity to identify Alzheimer's disease before dementia develops.

Predementia constructs: Mild cognitive impairment or mild neurocognitive disorder? A narrative review

“…44 The incidence of MCI also increases with age (range, 20-75 cases per 1000 persons/years). 45,46 These data on MCI prevalence and incidence differ depending on the origin of the studied cases (higher in clinical settings than in population surveys), 11,30,37,39,[45][46][47][48][49][50][51][52][53][54][55][56][57][58] type of diagnosis (algorithmic vs. clinical judgments), 39 and, obviously, the age of the population (higher in older samples). 11,30,37,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] Several studies have reviewed the evolution of MCI and its rates of conversion to dementia, which is one of the most important clues in this diagnosis.…”

“…This risk could be estimated by the annual conversion rate from MCI to dementia, that is, ∼10% in clinical settings, but only ∼5% in community surveys, where ∼1%-2% of the cognitively normal people convert to dementia. 11,30,[37][38][39][47][48][49][50][51][52][53][54][55][56][57][58] Studies always confirm that MCI cases have higher dementia risk than cognitively normal people (ranging from 2.5 to nearly 9 times higher) 11,30,37,39,46-58 ; exceptionally higher conversion rates are also described. 57 Only a limited number of MCI cases in population-based cohorts develop dementia, whereas the majority remain stable [47][48][49][50][51][52][53][54][55][56]59 ; the data presented in Tables 2 and 3 are taken from our epidemiological survey and illustrate this fact.…”

“…According to several studies, the cognitive characteristics of MCI may have prognostic value. Some of the studies stressed the intensity of memory loss 58,65,67,68 but others emphasized the importance of executive dysfunction to predict dementia conversion. 69,70 In second, their quantification has prognostic value for dementia conversion.…”

Mild Cognitive Impairments Attenuate Prefrontal Cortex Activations during Walking in Older Adults

“…Mild Cognitive Impairments (MCI) is an established risk factor for Alzheimer's dementia [1]. The presence of MCI is determined via established diagnostic procedures requiring evidence for objective cognitive impairment [2] based on performance cutoff scores on a neuropsychological tests [3].…”

Aggregation of Abnormal Memory Scores and Risk of Incident Alzheimer’s Disease Dementia: A Measure of Objective Memory Impairment in Amnestic Mild Cognitive Impairment

“…However, impairment in these classifications is either not explicitly defined (Graham et al, 1997;Winblad et al, 2004) or variably defined as 1 (Crook et al, 1986;Levy, 1994), 1-1.5 (Albert et al, 2011), 1.5 (Petersen et al, 1995) or 1-2 (American Psychiatric Association, 2013) SD below the normative mean. This heterogeneity undermines the reliability of MCI as a construct and may compromise its predictive validity because consistent models of prediction cannot be developed (Bradfield & Ames, 2020).…”