Background
Parkinson’s disease (PD) is one of the most common neurodegenerative diseases worldwide, with a prevalence ranging from 31–201 per 100,000 population [
1]. The symptoms of PD encompass motor features such as rigidity, bradykinesia, tremor and postural instability [
2], and non-motor symptoms including impairment of olfaction, vision, sleep, salivation, gastric and bowel function, sebaceous gland activity, and mood and cognition [
3]. PD diagnosis is based upon the presence of a set of cardinal motor signs; progression is defined by the degree of motor disability; management is primarily directed towards improving motor symptoms [
2,
4].
Persons with PD are particularly vulnerable to deterioration of health-related quality of life (HRQoL) resulting from significant motor disability and the burden of non-motor symptoms. Assessment of HRQoL of persons with PD is thus of essential importance. Several factors have been reported to be associated with low HRQoL. Among motor symptoms, the most significant determinants affecting HRQoL are disease severity, motor complications, postural instability and gait disorder [
5‐
7]. Among non-motor symptoms, depression, anxiety, cognitive impairment, fatigue, pain, urinary disturbances and sleep problems were found to be the most significant determinants of HRQoL [
5,
8,
9]. Among other factors, a high levodopa equivalent daily dose and comorbidities were found to be prevalent and independent determinants of HRQoL [
6]. Parallel to the clinical features, several socio-demographic factors such as level of education and number of people in a household have been described as independent determinants of HRQoL [
5,
7].
Most previous studies however have assessed only a limited number of factors in relation to HRQoL. The impact of certain variables (
e.g. rural living, marital status, education, comorbidities) have been infrequently systematically studied. The main aim of our study therefore was to evaluate the impact of a wide range of socio-demographic and clinical factors upon the HRQoL of a cohort of persons with PD in Estonia. We also focused on the non-motor symptoms identified by the new version of the Movement Disorder Society Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) Part I, which has recently been adopted and validated [
10].
Discussion
The purpose of this study was to investigate factors that may contribute to low HRQoL in persons with PD. We found that the main clinical determinants of low HRQoL in persons with PD were depression and the high burdens of motor and non-motor aspects of daily living. None of the investigated socio-demographic variables significantly associated with HRQoL.
Depression has an average prevalence of about 40 % among persons with PD [
20] and is a recognized predictor of low HRQoL. As previous studies [
5,
8], we found depression to be one of the most significant determinant of HRQoL. A study by Leentjens
et al. [
21] demonstrated that the risk factors in the general population for depression—such as older age, female gender, somatic comorbidities, and personal and family history of depression—also predict depression in persons with PD. In our sample the prevalence of depression in female patients was significantly higher than in male patients (58 % and 43 % respectively, p = 0.0189). In addition to BDI, depression was more often reported by women according to Part IA of the MDS-UPDRS. Studies examining gender differences regarding prevalence of depression have yielded inconsistent results. While van der Hoek
et al. [
22] found no difference in the prevalence of depression in male and female persons with PD, Solla
et al. [
23] found prevalence of depression significantly higher in female persons with PD. The reason why women are more disposed to depression might partly be explained by the greater exposure of competing risk factors, as suggested by Sonnenberg
et al. [
24] who demonstrated this association in a study on gender differences for depression in the elderly of a general population: controlling for age, comorbid somatic disease, and a number of other risk factors reduced the relative risk of depression in women by more than a half. The female patients in our study were slightly older than the male patients, were more often widowed and had a higher mean number of comorbidities. Men in our cohort were significantly more often married and lived together with their wife and or children. Based on the studies by Sonnenberg
et al., it could be assumed that controlling for several factors associated with social and health status might reduce the relative risk of depression in female persons with PD.
In recent years there has been increasing evidence suggesting that the impact of non-motor symptoms on HRQoL is more important than the impact of motor features [
8,
9]. Similar to previous studies, our study revealed that HRQoL was significantly lower with higher loads of non-motor symptoms. All non-motor symptoms correlated significantly with PDQ-39 SI, except the features of ICDs: a heterogeneous group of pathological behaviours associated with dopamine replacement treatment that include pathological gambling, compulsive sexual behaviour, compulsive shopping, and binge eating, together with pounding and the addiction-like compulsive use of dopamine replacement therapy [
25]. A case study by Voon
et al. indicated that patients with ICDs have more depressive symptoms [
26]. We did not find a statistically significant difference between mean BDI scores for persons with PD and with ICDs (based on positive item 1.6 in MDS-UPDRS Part IA), and persons with PD and without ICDs. Reducing the dosage or discontinuing the administration of dopaminergic agonists or substituting another drug from this group is a frequently effective therapeutic measure [
25,
27]. Only a few studies on the impact of ICDs on HRQoL have been published and some found controversial results,
i.e. ICDs as a predictor of lower HRQoL [
28,
29], but in other studies [
30] ICDs did not affect HRQoL. The current study did not reveal a negative impact of ICDs on quality of life. Our finding is supported by a study by Ondo, where only 18 % of patients with increased impulsivity felt that the change was deleterious [
30]. Our daily clinical practice suggests that ICDs cause considerable distress to patients’ families or caregivers, but the patients themselves are not that annoyed by these behaviours. Out of the 268 patients screened in our study, 7.8 % (n = 21) complained of ICDs. It could be assumed that at least one reason why ICDs did not correlate significantly with HRQoL is that the pathological behaviours were relatively mild. About half (52 %) of these patients reported only slight problems with behavioural disturbances and it could be that the problems did not yet affect their social and occupational functioning.
Dependency in activities of daily living as assessed using the SE-ADL scale and disability in the performance of daily living experiences as measured by the previous version of the UPDRS Part II, have been found to be significant contributors to HRQoL [
5]. In a recently published study by Rodriguez-Blazquez
et al. [
31], who used the MDS-UPDRS Part II, a significant negative association between the more advanced disability and HRQoL occurred. The current study demonstrated that disability evaluated by SE-ADL and MDS-UPDRS Part II significantly contributed to lower HRQoL. However, motor symptoms (MDS-UPDRS Part III) were not an independent predictor of HRQoL. Even though for antiparkinsonian treatment Part III with motor assessments is of high importance, it can be seen that for HRQoL, the self-assessment of non-motor symptoms and ability to perform daily activities have more impact.
An axial impairment has been shown to be associated with reduced HRQoL in persons with PD [
6]. We found that patients with postural instability and gait disorder dominance had significantly lower overall HRQoL compared to patients with tremor dominance or hypokinetic-rigid dominance; however, in multiple regression analysis it did not appear to be an independent predictor of HRQoL. Neither was HY stage found to be an independent predictor, though patients with more severe PD (HY ≥3) had lower HRQoL than patients with milder PD. The results of the multiple regression analysis were concordant, as higher HY stages reflected an axial involvement with balance and gate impairments. Persons with PD in general, but particularly in patients with the postural instability and gait disorder, are likely to become less able to move around inside their homes and out in the community. They also become more prone to falls as the disease progresses. Regular physical exercise is associated with higher HRQoL, mobility, physical function, slowing the progression of the disease, lower caregiver burden, and less cognitive decline [
32]. In view of this, patients with the postural instability and gait disorder may benefit most from education on using rehabilitation activities (
e.g. physical exercise, physiotherapy) and assistive devices (
e.g. reaching aids). Therefore, in addition to pharmacological treatment, the management of PD should include rehabilitative care, which helps to maintain patients’ ability to participate in daily living activities and avoid the decline of HRQoL.
In our study socio-demographic characteristics including age, gender, urban/rural living, level of education, marital status and living alone/with others, did not significantly affect overall HRQoL. However, we found several associations between these factors and domains of PDQ-39. Women received lower scores for emotional well-being and bodily discomfort, which is in accordance with the study by Carod-Artal
et al. [
5]. As regards to patients’ living status, those who lived alone received lower scores for emotional well-being compared with patients who lived with others. Another study by Winter
et al. showed that patients living alone had worse HRQoL than patients living with somebody [
7]. Our results did not reveal any statistically significant difference in HRQoL among patients with different educational backgrounds, whereas greater number of years in education was found to be associated with higher HRQoL in a study by Carod-Artal
et al. [
5]. Klepac
et al. [
33] found that rural patients had lower overall HRQoL, with most of the domains of PDQ-39 affected. In contrast, the results of our study suggest that living area is not associated with overall HRQoL. Moreover, our results showed that patients living in rural areas had significantly less stigmatization and better social support than patients living in urban areas.
The study has some methodological limitations that ought to be recognized and taken into account when interpreting the findings. The analysis was based on clinical data collected at a single point in time; therefore, any pattern of progression of the disease could not be estimated. Also, we cannot exclude the possibility that some of the variables, such as gender (female patients outnumbered male patients) or stage of disease (62.6 % of patients had HY ≥3) could have influenced the results found.
The strength of the study was the relatively large sample of persons with PD, which included institutionalised and severely ill patients, and thus was representative of the PD population as a whole. The study participants were also evaluated with a wide range of clinimetric properties that covered motor, non-motor, functional, cognitive and emotional aspects.
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Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
LKE collected data, interpreted the results, and drafted the whole manuscript. MR performed the statistical analysis and contributed in interpretation of data. TP and MM contributed to the acquisition of data. PT was involved in the study design, data collection, drafting the manuscript, and gave the final approval of the version to be published. All authors read and approved the final manuscript.