Differences in trajectories of quality of life according to type of dementia: 6-year longitudinal findings from the IDEAL programme.

Background: People with different types of dementia may have distinct symptoms and experiences that affect their quality of life. This study investigated whether quality of life varied across types of dementia and over time.

Methods: The participants were 1555 people with mild-to-moderate dementia and 1327 carers from the IDEAL longitudinal cohort study, recruited from clinical services. As many as possible were followed for up to 6 years. Diagnoses included were Alzheimer's disease, vascular dementia, mixed Alzheimer's and vascular dementia, Parkinson's disease dementia, dementia with Lewy bodies, and frontotemporal dementia. Self- and informant-rated versions of the Quality of Life in Alzheimer's Disease scale were used. A joint model, incorporating a mixed effects model with random effects and a survival model to account for dropout, was used to examine whether quality of life varied by dementia type at the time of diagnosis and how trajectories changed over time.

Results: The strongest associations between dementia type and quality of life were seen around the time of diagnosis. For both self-ratings and informant ratings, people with Parkinson's disease dementia or dementia with Lewy bodies had lower quality of life scores. Over time there was little change in self-rated scores across all dementia types (- 0.15 points per year). Informant-rated scores declined over time (- 1.63 points per year), with the greatest decline seen in ratings by informants for people with dementia with Lewy bodies (- 2.18 points per year).

Conclusions: Self-rated quality of life scores were relatively stable over time whilst informant ratings showed a steeper decline. People with Parkinson's disease dementia or dementia with Lewy bodies report particularly low levels of quality of life, indicating the importance of greater attention to the needs of these groups.