Main findings
Using dyadic analysis methods, this study suggest a potential impact of subtype diagnosis on capability to live well in both people with dementia and carers. People with non-AD subtypes, including VaD, mixed VaD/AD, PDD and LBD, had a lower capability to live well than those with AD. For carers, those caring for people with PDD and LBD reported lower scores on living well measures than carers of people with AD. Further adjustment for comorbidity attenuated differences between AD, VaD and mixed AD/VaD, but PDD and LBD continued to have a particularly strong impact on capability to live well in both people with dementia and carers.
Strengths and limitations
The IDEAL study included a large number of community-dwelling people with dementia and their carers across Great Britain. In addition to major subtypes (AD and VaD), people with rare subtypes were also recruited and were represented by at least 40 dyads in this study population. The interviews included multiple measures of living well, including aspects of quality of life, life satisfaction and wellbeing for both people with dementia and their carers. The method of dyadic analysis was used to investigate the association between subtypes and capability to live well in both people with dementia and carers and to take into account correlations within dyads.
To be eligible to take part, participants needed to have a clinical diagnosis of dementia and a MMSE score of 15 or above. People with severe dementia were not included in the study, and the dyadic association between subtypes and capability to live well might be different in this group compared to the current study population focusing on mild to moderate dementia. Given our interest in the dyadic relationship, this analysis mainly focused on participants with carers. Since those without carers might have better health status and functional ability and in some cases might not need a carer, the association between subtypes and capability to live well might be different in this group. Nevertheless, similar results were found in sensitivity analyses including all participants irrespective of carer involvement (N = 1547); therefore, this should have a minimal impact on the main findings.
The diagnoses of dementia subtypes were made by different clinicians across the country. Variation in clinical practice and potential diagnostic misclassification could not be addressed in this analysis. However, a clinical diagnosis reflects the experience of people with dementia and their carers attending health services and leads to selection of particular treatments and disease management plans. Different measures for quality of life were used in people with dementia and the carers, and therefore changes in quality of life scores were not directly comparable. To generate an overall score for quality of life in carers, six independent domains in WHOQOL-BREF were combined using factor analysis. Although measures for quality of life were different for people with dementia and carers, this study mainly focused on relative differences, and similar patterns were found in these two quality of life measures.
Interpretation of results
People with non-AD subtypes had a lower capability to live well than those with AD. When further adjusting for comorbidity, the difference between AD, VaD and mixed AD/VaD reduced considerably. This suggests that the burden of chronic conditions might explain much of the observed differences across these subtypes. Although the diagnosis of VaD is based on cerebrovascular pathology and small vessel disease, people with VaD might also experience physical disabilities as well as language and visuospatial deficits due to stroke and heart attack and thus may have poor quality of life and wellbeing [
8].
People with PDD and LBD continued to show a particularly poor capability to live well, even when we further adjusted for the number of chronic conditions. This corresponds to findings from previous studies [
9‐
11]. These two subtypes are closely related, and the differential diagnosis is largely based on when symptoms first appear. The core symptoms of LBD, including fluctuating cognition, visual hallucinations and spontaneous features of Parkinsonism [
8], may have a relatively large impact on daily life compared to the major symptoms of memory loss in AD. A higher number of autonomic symptoms such as fatigue, postural dizziness and mucosal dryness have also been reported in PDD and LBD than in AD [
21]. PDD is also associated with high comorbidity [
22,
23], and the mix of physical, emotional and cognitive changes might have a negative impact on quality of life for the person with dementia as well as their carer. Carers of people with PDD and LBD have been reported to experience a higher level of stress than carers of those with AD and VaD [
24]. This might be due to the challenges of responding to symptoms such as hallucinations, motor disability and functional impairment in PDD and LBD [
11].
The literature has suggested a greater burden of care in FTD [
12,
13]. FTD generally occurs in younger age groups (< 65) and includes symptoms related to changes in personality, behaviour and function [
7]. Although these symptoms may plausibly increase the burden of caregiving and cause poor quality of life and wellbeing, this study did not find a difference in the capability to live well between carers of people with FTD and AD. A previous study from Australia has reported variation in caregiving burden across different FTD variants [
12]. Although carers of persons with behavioural variant FTD (bvFTD) did report a particularly high burden, carers for people with other FTD variants, including semantic dementia and progressive non-fluent aphasia, had similar levels of burden to carers of people with AD. Indeed, the mean scores for living well measures were found to be lower for the 10 IDEAL carers of people with bvFTD than for carers of people with other FTD variants. However, it is not possible to test differences within this subtype based on such a small sample size and limited statistical power. In addition, this study population only included those with mild to moderate dementia and did not include those with advanced FTD.
Dyadic modelling was used to consider the capability to live well in both people with dementia and carers and to account for correlations within dyads. In addition to relative differences across subtype, this study also reveals baseline differences between people with dementia and carers through this dyadic analysis approach. Capability to live well was clearly not independent in these dyads, but relative difference across subtype, a dyad-level measure, was not considerably affected by this correlation. However, absolute scores on living well measures were lower for carers than for people with dementia. Despite variation across subtypes, baseline scores for life satisfaction and wellbeing in carers were close to those for participants with PDD and LBD, who had the worst capability to live well. This indicates that carers generally reported a poorer capability to live well than people with dementia, regardless of subtype.
Clinical implications and future research directions
Variation in capability to live well was found across dementia subtypes, particularly PDD and LBD. Guidelines for dementia care may need to be tailored for different subtypes and provide additional support for these high-risk groups. Since the impact of living with VaD and mixed AD/VaD may be related to comorbidity, treatment of hypertension and vascular diseases is important for those with these subtypes. Health professionals who provide post-diagnostic support and care may need to pay more attention to the PDD and LBD subtypes and consider potential approaches to improve quality of life and wellbeing for both people with dementia and their carers [
25]. In addition to medical treatments, some non-pharmacological interventions might support those living with PDD and LBD to maintain daily function. For example, a recent pilot randomised controlled trial focusing on 29 people with PDD and LBD has suggested that cognitive rehabilitation, an individualised approach addressing personally relevant goals, can be effective in managing the impact of the cognitive difficulties on daily life and in improving quality of life [
26]. Future intervention studies may extend this approach to include the physical symptoms seen in PDD and LBD and reduce the combined impact of cognitive and physical symptoms on the capability to live well with these conditions. Carers reported relatively low scores on living well measures across all dementia subtypes. Burden of caregiving appears to be an important issue, and appropriate support for family carers is vital [
1].
To reduce the impact of subtype diagnosis, future research may focus on identifying specific factors related to the quality of life and wellbeing in PDD and LBD and developing potential interventions to improve disease management in people with dementia and carers. In addition to medications, psychosocial and rehabilitative interventions may play an important role in addressing neuropsychiatric and behavioural symptoms and general physical, psychological and social health [
27].