Cognitive and functional progression of dementia in two longitudinal studies

Abstract

Objectives: Previous studies have identified several subgroups (ie, latent trajectories) with distinct disease progression among people with dementia. However, the methods and results were not always consistent. This study aims to perform a coordinated analysis of latent trajectories of cognitive and functional progression in dementia across two datasets.

Methods: Included and analyzed using the same statistical approach were 1628 participants with dementia from the US National Alzheimer's Coordinating Center (NACC) and 331 participants with dementia from the Dutch Clinical Course of Cognition and Comorbidity study (4C-Study). Trajectories of cognition and instrumental activities of daily living (IADL) were modeled jointly in a parallel-process growth mixture model.

Results: Cognition and IADL tended to decline in unison across the two samples. Slow decline in both domains was observed in 26% of the US sample and 74% of the Dutch sample. Rapid decline in cognition and IADL was observed in 7% of the US sample and 26% of the Dutch sample. The majority (67%) of the US sample showed moderate cognitive decline and rapid IADL decline.

Conclusions: Trajectories of slow and rapid dementia progression were identified in both samples. Despite using the same statistical methods, the number of latent trajectories was not replicated and the relative class sizes differed considerably across datasets. These results call for careful consideration when comparing progression estimates in the literature. In addition, the observed discrepancy between cognitive and functional decline stresses the need to monitor dementia progression across multiple domains.

Keywords: cognition; coordinated analysis; daily functioning; dementia progression; growth mixture model; trajectory.

Figure 1

Fitted and observed Mini‐Mental State Examination (MMSE) and Functional Activities Questionnaire (FAQ) trajectories in the National Alzheimer's Coordinating Center (NACC) dataset. MMSE and FAQ trajectories are shown in red and blue respectively. FAQ was reverse coded with higher scores indicating better daily functioning. A, The mean decline of the sample (N = 1628). B, Class 1—slow decline in MMSE and FAQ (N = 406 [25%]). C, Class 2—moderate decline in MMSE and rapid decline in FAQ (N = 1137 [70%]). D, Class 3—rapid decline in MMSE and FAQ (N = 85 [5%]). The trajectories of individual participants are shown in thin lines. The average trajectories of the whole sample and the mean trajectories of each class are shown in bold lines. Note that individuals were assigned to each class based on their most likely class membership. Therefore, the numbers of participants in each class are slightly different from those in the manuscript text and Appendix S2 [Colour figure can be viewed at http://wileyonlinelibrary.com]

Figure 2

Fitted and observed Mini‐Mental State Examination (MMSE) and instrumental activities of daily living (IADL) trajectories in the 4C dataset. MMSE and IADL trajectories are shown in red and blue, respectively. IADL was recoded with a scale of 0 to 30. A, The mean decline of the sample (N = 331). B, Class 1—slow decline in MMSE and IADL (N = 264 [80%]). C, Class 2—rapid decline in MMSE and IADL (N = 67 [20%]). The trajectories of individual participants are shown in thin lines. The average trajectories of the whole sample and the mean trajectories of each class are shown in bold lines. Note that individuals were assigned to each class based on their most likely class membership. Therefore, the numbers of participants in each class are slightly different from those in the manuscript text and Appendix S2 [Colour figure can be viewed at http://wileyonlinelibrary.com]