Patterns of Cognitive Decline Prior to Dementia in Persons with Mild Cognitive Impairment

Abstract

Only a limited number of studies have investigated the decline of discrete cognitive domains as individuals progress from mild cognitive impairment (MCI) to dementia. Thus, the goal of this longitudinal study was to evaluate the cognitive changes underway during the years preceding a diagnosis of probable Alzheimer’s disease (AD), and to compare these changes to those found in MCI participants who do not progress to dementia. Participants were compared as a function of whether they later converted to AD (n = 47) or not (n = 74). Cognitive change was assessed prior to the conversion year, using that year as a starting point. A combination of polynomial regression analyses and mixed ANOVAs assessed 1) the trajectory of cognitive decline for each domain and 2) the differences between non-progressors and those who had converted to AD. The different cognitive domains demonstrated very different patterns of decline in the group of MCI progressors. A quadratic function, i.e., many years of stable performance followed by a rapid decline just prior to diagnosis, was observed for delayed recall, working memory, and spatial memory. In contrast, a gradual linear decline was observed for immediate recall, executive function, and visuo-spatial abilities. Finally, language in progressors was impaired on all time periods relative to non-progressors, but there was no further change between the first assessments and conversion to AD. Individuals with MCI who progress to AD show abnormal cognition at least two years prior to their dementia diagnosis. The pattern of symptom change observed appears to depend upon the cognitive domain and thus, clinical studies should not assume similar rate of decline across domains. In contrast and, apart from verbal memory, the non-progressors present a performance similar to that of healthy older adults.

Predictors That a Diagnosis of Mild Cognitive Impairment Will Remain Stable 3 Years Later

“…While some of our more influential predictors are similar to those identified by studies of conversion, risk factors for conversion such as education, sex, ethnicity, MCI subtype, and executive function (Campbell et al, 2013; Cloutier et al, 2015; Lee et al, 2012; Ye et al, 2013; Yoon et al, 2015) did not appear to be influential in predicting MCI stability in our overall predictive model. Further, we found that cardiovascular risk factors did not distinguish MCI-stable individuals from converters, indicating that vascular burden does not significantly affect MCI stability over 3 years.…”

Language Performance of Individuals at Risk for Mild Cognitive Impairment

“…The value of using a broad-based test battery with language performance measures, as well as measures of other key cognitive abilities, as recommended by the NIA-AA MCI workgroup (Albert et al, 2011) and the American Psychiatric Association (2013), cannot be overstated. As previously noted, many etiologies are associated with MCI and can present with deficits other than memory or language impairment, for example, visual spatial impairment (Cloutier, Chertkow, Kergoat, Gauthier, & Belleville, 2015;Fujimori et al, 1998;Possin, 2010).…”

Combining Cognitive Markers to Identify Individuals at Increased Dementia Risk: Influence of Modifying Factors and Time to Diagnosis

“…Although it was clear that the cognitive markers were better predictors of dementia closer to diagnosis, the relative importance among the predictors did not appear to substantially change over time. It has been shown that the rate of cognitive decline in the preclinical phase differ across cognitive domains (Cloutier et al, 2015;Grober et al, 2008;Thorvaldsson et al, 2011), suggesting that different domains may be more or less useful for predicting future dementia depending on time until diagnosis. However, using the scores from single points in time (as opposed to investigating rate of decline), this study rather points to the same domains being the most predictive of future dementia.…”

“…Longitudinal studies mapping rates of decline suggest that some cognitive domains start to decline earlier and some later in relation to the dementia diagnosis, and they may follow different trajectories (Cloutier, Chertkow, Kergoat, Gauthier, & Belleville, 2015). Thus, different cognitive domains may be more or less useful in predicting future dementia depending on time to diagnosis.…”