Our study found that among institutionalized older people both severity of NPS and severity of dementia were significant factors determining HRQoL and they had a significant interaction. Surprisingly, a higher total NPI score was associated with better HRQoL in residents with severe dementia, whereas among those residents with mild–moderate dementia this association was not seen. In severe dementia, higher HRQoL correlated with higher points in all subsyndromes of NPI. In severe dementia, higher score in NPI correlated positively with functional dimensions of 15D (mobility, usual activities, eating, speech, excretion, and mental function) as well as vitality, whereas in mild–moderate dementia lower NPI score correlated with lower levels of distress and depression as well as vitality.
These findings highlight the importance of both severity of dementia and burden of NPS in HRQoL. NPS seem to have a distinct impact on HRQoL at different stages of dementia. Low functional capacity seems to be linked to both low number of NPI and low HRQoL among those with severe dementia. A possible explanation for these results may be that when dementia progresses to a severe stage with a high number of disabilities the residents have less capacity to present NPS, leading to a low NPI score but worse HRQoL. Several dimensions of 15D measure functioning. Therefore, it is understandable that those residents with severe dementia and slightly better capabilities of functioning score also better in 15D. Interestingly, vitality in severe dementia indicated higher NPI score, whereas it was associated with lower NPI score in mild–moderate dementia. Among residents with mild–moderate dementia, lower NPI scores logically correlated with less depression and distress.
Furthermore, in severe dementia higher HRQoL correlated positively with all subsyndromes of NPI. In mild–moderate dementia, there was no such correlation. Our study cohort comprised only 109 long-term care residents with mild–moderate dementia, so the results should be interpreted with caution for patients in earlier stages of dementia.
NPI scores among our residents were rather low, mean NPI total score being 12, but this is consistent with other studies from long-term care [4, 15, 35, 36]. Studies of home-dwelling people with dementia have found higher NPI scores [14, 16, 37]. This difference may be partly explained by the properties of NPI as an assessment tool. The assessment comes from a third-party perspective. The care staff in long-term care or the caregivers in the case of home-dwelling people with dementia may have different perceptions of the severity of symptoms encountered . Care staff might minimize the burden of symptoms, accepting the behavior as part of the dementia disorder and emphasizing their professionalism in being able to take care of the various symptoms of their residents, whereas an informal caregiver might find him/herself in a stressful situation without any formal education, resulting in the same symptoms causing more distress.
The multiple different instruments used in previous studies assessing quality of life in people with dementia complicate comparison between studies. Most of these instruments are disease specific and measure mainly mood, behavior, social relations, and well-being. In our study, we used the 15D instrument in which various dimensions measure functioning. The generic 15D instrument has been compared with the disease-specific QoL-AD and has been reported to evaluate different aspects of quality of life, for example general health correlated with 15D but not with the QoL-AD scores, whereas depressive symptoms correlated inversely with QoL-AD but not with 15D .
Our study found dementia severity to be a significant factor determining HRQoL. This is in concordance with two systematic reviews that noted a negative association between proxy-rated quality of life and dementia severity [39, 40]. The association between dementia severity and quality of life has also been reported by a recent cross-sectional cohort study in long-term care in the Netherlands . In previous studies, dementia severity has also been associated with a higher prevalence of NPS in both long-term care and home-dwelling people with dementia [16, 19, 41, 42]. In our data, NPS burden was not associated with dementia severity according to MMSE or CDR. This difference might be partly explained by the different study groups. The participants of our study had overall a more severe stage of dementia, the mean MMSE being only 6.8.
In our study, a higher NPS burden was associated with better HRQoL. This result is contradictory to most previous studies showing that having NPS impairs quality of life [10,11,12,13,14,15,16]. To our knowledge, only one earlier study on quality of life in nursing home residents found that a higher NPI had a positive influence on the course of quality of life . In this study, the cognition of the residents was also rather low, mean MMSE being 7.1, which is similar to our study population. Thus, one explanation for why our results differ from most previous ones seems to be partly due to characteristics of the study population. The other studies have examined earlier stages of dementia and have had less participants with severe dementia.
Interestingly, in our study the use of both anticholinergic medication and Alzheimer medication was associated with a higher severity of NPS. Due to the cross-sectional nature of our study, we do not know whether this is due to adverse effects of the medication or the fact that the residents using these medications had had even more severe symptoms before drug initiation. The use of Alzheimer medication is very high due to Current Care Guidelines which in Finland recommend Alzheimer medication as the first-line drugs for NPS. The use of psychotropic medication was alarmingly high in all NPI groups, but there was no difference between the groups.
Limitations of our study include the cross-sectional design, which limits the possibilities of drawing conclusions about causal relationships. Care staff rating of residents’ HRQoL may also be considered a limitation. However, this method was intentionally chosen because of the high prevalence of severe dementia, which could have compromised self-reporting. It is known from previous research that there are differences between caregiver and self-rated quality of life [10, 16, 39]. Residents tend to consider their quality of life as significantly higher than caregivers. Assessments of residents were performed by the member of staff who knew each particular resident best in order to increase the validity of the data. In addition, 15D can also be rated by a proxy . The study population was long-term care residents with advanced dementia and, therefore, the results cannot be generalized to other populations with dementia. Even though CDR scale is one of the most well-known and well-studied dementia staging instruments, it is however not without limitations. CDR score addresses both cognition and physical functioning but it may also be influenced by physical comorbidities. Another limitation is that pain, a possible confounder, was not assessed in our study.
An important strength of our study is the large sample size and the use of a large number of well-validated variables. Residents were assessed by well-trained study nurses using the same data collection instruments and methodology, resulting in high validity of the data. Eighteen of the 54 nursing homes in Helsinki were included in this study. The baseline characteristics and HRQoL measured in 15D were similar to those of the total long-term care population in Helsinki; thus, our study cohort was representative . Another important strength is that, to our knowledge, no other study has previously examined the impact of the severity of NPS on HRQoL, nor have the interaction effects of dementia severity and NPS on HRQoL been investigated. Thus, these results make an important contribution to our understanding of the factors associated with HRQoL in institutionalized older people with dementia.