In this study, patients rated significantly higher QoL than the caregivers, which is in accordance with the literature.
Cognition, sleepiness and depression were associated with the self-rated QoL, while basic and instrumental activities of daily living were associated with the proxy rated QoL.
PwAD described a better quality of life as their cognitive level decreased. Poor quality of life was found to be associated with daytime sleepiness and depressive symptoms. In terms of caregivers, a more independent life means a better quality of life for the PwAD. If the total score of the quality-of-life scale were taken into account, it would be seen that only the patient's depressive symptoms negatively affected his quality of life and also there would be seen no relationship with other symptoms. For these reasons, both the reports of patients and proxies should be considered.
According to the results of our study, self- and proxy rated QoL are not related to age and disease duration. In previous studies, it is seen that the effect of age and duration of illness is a controversial issue on QoL of PwAD (11, 12, 19, 21, 22). Similar to our study, Dewitte et al (12) showed there is no relationship between age and quality of life, but, unlike our results, Andrieu et al (11) and Hongisto et al (22) have shown that proxy rated QoL is affected by the disease duration. According to these 2 and 5-year follow-up studies, the quality of life reported by the patient's caregiver has significantly decreased due to disease progression, functional and behavioral disorders. On the other hand, PwAD, did not change the quality of life during the disease process as they developed a mechanism to cope with the new difficulties they encountered. Decreasing patient awareness ensures that the quality of life is not affected by the disease duration (21).
Our results show that, caregivers assumed the patient's QoL with impaired cognition worsens, but this relationship was not statistically significant. When examined from the perspective of the patient, it is seen that the quality of life increases with cognitive impairments, supporting the literature (23–25). In Stites at al.’s study, PwAD who are aware of the diagnosis and the disease report more stress and depression, and poorer quality of life. Quality of life does not show a linear relationship with the disease. In a study comparing mild cognitive impairment (MCI), mild AD, and healthy individuals, MCI patients reported worse quality of life than AD and healthy individuals (25). According to this study of Stites et al., in the MCI grup awareness is high because their cognitive loss is lower, and therefore the perception of quality of life is poor. In our study, the negative correlation between quality of life and MMSE supports this result. As a health policy, early diagnosis is important, but when we consider our results, how to inform the patient with early diagnosis is also an important situation. Information should be given about psychological changes, in addition to the physical changes that may be seen in patients. Thus, in the earlier stages when there is awareness, there may be a milder situation.
Depression and sleepiness, that are consistent with previous research, were also correlated and contributed to lower self-rated QoL (9, 26–29). Depression, which is perceived and evaluated personally, is an important risk factor that also affects the quality of life, decreasing the brain's ability to cope with disease. As stated in previous studies, severe PwAD reject depressive symptoms, while mild to moderate patients show psychological distress. For these reasons, depression should be considered as a treatable condition from the early stages when awareness is higher and should be treated with the most appropriate approaches for the patient.
Similar to our study, Barbe et al, that measures the quality of life with OoL-AD (3 scores; patient, caregiver and overall), examined the associations of between the depression and the 13 items of the QoL-AD (30). In the both patient reports and caregiver reports, the presence of depression influenced the 3 items of QoL which consist of mood, ability to do things for fun and life as a whole. Instead of an extra depression evaluation, using these quality-of-life items may provide convenience. Studies are needed for this aim.
Another result of our study is that there is an association between the high level of daytime sleepiness and the worse quality of life. Sleep disorders and abnormal circadian rhythms are important problems which are seen in 25–60% of PwAD (9, 29, 31). According to Petrovsky et al’s state of the art review, although sleep disorders are common, there is no study that summarizes how they affect QoL (29). It also causes stress for the caregiver because of leading different health-related problems in patients (depression, heart disease, decrease in functional capacity, etc). As can be seen from our results, patient’s socialization is reduced due to excessive daytime sleepiness and accordingly their own quality of life perception decreases. Sleep, should be considered as a treatable factor affecting quality of life and take a part of PwAD's routine evaluation.
Activities of daily living are one of the important issues investigated in the dementia group (12, 31–35). In our study, according to the statement of PwAD caregivers, better quality of life of patients is related to their independence in activities of daily living.
Subjective Cognitive Disorders (SCD), is an important stage in which cognitive complaints occur before AD diagnosis. Since psychological conditions such as depression-anxiety also cause SCD, it is difficult to distinguish at this stage. Roehr et al (34) found that if SCD diagnosed patients have disabilities in IADL, they are likely to be diagnosed with AD in the future. Due to the awareness of caregivers, IADL is an important point that should not be neglected during the disease process.
Executive functions and ADLs are more important by the caregiver (12). According to the results of the Barbe et al.'s study, being able to move and use the telephone creates self-esteem and provides a better perceived quality of life (31). Therefore, it is important to create a rehabilitation programme for an activity related to quality of life.
There are some limitations should be considered while interpreting this study's results. Non-inclusion of severe PwAD is one of the limitations of this study. The rate of PwADs staying in nursing homes has also increased due to the increase in disease's incidence and care needs. Therefore, another limitation of this study was the participation of only PwADs living in the community. Considering these limitations for future studies, it is recommended to plan more comprehensive studies.