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.
