Parkinson’s Disease (PD) is major geriatric neurodegenerative diseases, along with dementia and stroke, and its incidence rate is increasing worldwide as being an aging society [1]. According to data from the National Health Insurance Review and Assessment Service (NHISS) [2], the number of PD patients has increased from 71,571 in 2010 to 125,927 in 2020, an increase of 1.8%. Based on statistics for 2020, PD patients aged 70 years or older account for more than 83.5% of Parkinsonian syndrome cases. Also, 31.6% of male, 68.4% of female showed that female Parkinson's patients were twice as likely as male Parkinson's patients. The cost of PD treatment has increased from 384 billion won in 2016 to 483 billion won in 2020, a steady increase of 6% annually. Parkinson's patients’ costs are around 2 times higher than non-Parkinson's patients.

PD is a progressive neurodegenerative disease that leads to various motor and cognitive dysfunction. It is a serious disease accompanied by both physical and mental damaging effects on patients [3]. The dysfunction is accompanied by both physically and cognitive symptoms due to damages in neurons. Motor symptoms include tremors, rigidity, bradykinesia, and unstable posture. These symptoms result in limited self-care function, then often cause depression in PD patients [4]. Research has been conducted in other countries for the past 20 years to improve the quality of life of PD patients, but South Korea has been conducting research for the last ten years. The patients’ quality of life, cognitive function, and depression have been studied mostly in the fields of medicine, rehabilitation, and nursing, while quality of diet, well-being, and effects of exercise have been studied in the fields of nutrition and exercise [5].

Depression the most common non-motor symptom, is prevalent among adult neurological patients and occurs in 30~50% of patients with PD [6]. Depression occurs early phase of PD and negatively affects daily life performance and quality of life in patients suffering from PD [7]. Depression commonly occurs in the early stage of PD, and it not only affects physical disability, cognitive deterioration, and the quality of daily living, but it can also result in the misdiagnosis of either apathy or amnestic disorder related to dementia as depression with PD [5]. Therefore, depression management in PD patients improves individual well-being and becomes an evaluation index that indicates health status or therapeutic efficacy [6]. Since only the patient's symptoms are controlled and maintained among various therapeutic methods including pharmacological and non-pharmacological interventions, such as music therapy [8] are beneficial for depression in PD patients.

As the chronic illness progresses, the family must assume important responsibilities such as coping with their emotional state, role changes, efficient problem solving, and utilization of external resources [8]. Family function reflects the family's ability to satisfy the needs of the family members in terms of communication and sharing among the family members, and it is closely associated with the individual's health and illness [9]. It has been reported that the burden of care under long-term care, expectations when preparing to cope with the risk of fatigue, and family dysfunction negatively affect the physical and psychological state, and even the general well-being of the family caregivers [10]. It is necessary to enhance family function to improve the quality of life for PD patients [11]. Family functions were positively related to quality of life of caregivers of PD patients [12].

It is known that patients with serious symptoms of depression usually have low family function and have difficulty in normal life [13, 14]. Cancer patients who complain of severe symptoms of depression tend to come from broken homes and have poor quality of life when compared to patients with low levels of depressive symptoms or receiving palliative care [13]. Patients with type 2 diabetes show that depressive symptoms are related to family dysfunction and impaired quality of life. That is, depression was negatively related to family function and family function had a good influence on better quality of life in patients [14].

Previous studies have shown connections among patients’ depression, family function, and quality of life [13, 14]. There is research on the relationship between depression and quality of life [5, 7, 8] and is research on the relationship between family function and quality of life [11, 12]. Based on the finding that patients’ quality of life is closely related to psychological and family functioning factors, a relationship can be established among the three variables. Until now, the relationships among the three variables have not been identified for PD patients, thus it is the need to verify direct and indirect effects. This study aimed to examine the relationship among depression, family function, quality of life and validate the mediating effect of family function between depression and quality of life. This study is expected to showcase strategies to improve quality of life for PD patients.

Results of this study found that 77% of PD patients suffer from the symptoms of depression, with an average score of 23.37 points, indicating moderate depression. These findings were like more than 70% of the depressive prediction model studies in Parkinson's patients who showed these depressive symptoms [26]. There is a high risk for the progression of depression as the negative impact of depressive symptoms is more prominent relative to the symptoms of PD itself.

First, the present study found that depression in PD patients affects family function. In addition, the fact that the age of onset was found to be a factor affecting family function is the cause of family dysfunction because the sudden onset of illness brings on problems not only in the role of the head of household and supporting the family but also economic problems and psychological stress. The findings of the present and previous studies share common ground in that when PD patients suffer from high levels of depression, their family function and quality of life tend to be low. Previous cancer studies [13] have reported prevalence rates of 32% for depression and family function problems in 50% of cancer patients receiving palliative care.

PD is a progressive disease so a patient’s condition can worsen gradually. In that case, the patient’s family members must deal with constant pain, need to adapt to a whole new set of responsibilities, and care for the patient, which is very taxing and exhausting. In addition to the increasing physical hardship, financial burden, and little hope of complete recovery, families confront ever increasing suffering [9]. The adjustment process, such as the family caregiver adjusting to the care situation, developing appropriate coping strategies, and adjusting to changes in emotional and social support brings about changes in the functioning of the family [12].

Secondly, patients with low depressive symptoms showed high levels of family function and quality of life. The findings of the current study agree with the findings of a previous study, which depression affecting quality of life of the elderly in PD [27]. In addition, the showed that depression strongly impacts quality of life of PD patients [28]. Since depression due to PD affects physical disability, cognitive decline, and the difficulty of daily living [6], it can be understood that Gait disturbance and difficulty in daily activities can affect quality of life. It was found that depression had substantial negative association with impaired quality of life and low levels of depression can lead to better quality of life.

Thirdly, the analysis results showed a partial mediating effect of family function in that the explanatory power of depression directly influencing quality of life was 58%, whereas the explanatory power of depression influencing quality of life with family function acting as a mediating variable was 60%. The results showed that when depression of patients with PD worsens, the patient will have greater disability than patients without depression, and patient's depression directly influencing the quality of life. In this case, strengthening family function can ultimately improve the quality of life of the patient since it reduces the caregiving burden so that based on a positive relationship with the patient. Available methods of utilizing family members include family participation in nursing care planning, and organization of a self-help group communication program.

Similar findings were seen in a study of type 2 diabetic patients. There were links between depression, family function, and quality of life. When family function of type 2 diabetic patients was low, the quality of life was low and when the patient suffered from depression, impaired family function was evident [14]. Such a result indicates the necessity of education that increases bonding among family members and adaptability by having the family members participate when conducting an intervention for PD patients.

As a chronic degenerative disease progresses for an extended period, a fundamental measure of long-term patient care rather than a temporary one should be proposed [9]. The symptoms that change with the progression of disease bring unexpected stresses to the patient and the family since they frequently occur suddenly, and communication within the family can be affected not only by the illness but also by a series of psychological responses and coping strategies [12]. Conducting family therapy and counselling, for patients suffering from Parkinson’s disease and depression is recommended to improve family function so that patients with depression can find a new path to share their feelings with significant family members or to strengthen the family bonding and adaptability, or to educate the caregivers about the disease.

Finally, the present study investigated relationships among depression, family function, and quality of life of PD patients and the results showed that depression was associated with family dysfunction and impaired quality of life [13, 14]. Family function as a mediator contributed to depression and it in return contributed independently towards various dimensions of quality of life. When one of the most challenging issues for a family is how to maintain a functionally balanced mutual relationship, they often experience a profound crisis when new relationships must be figured out, and where the possibilities for closeness are often very different, limited, and skewed [21]. This study implies that family function is beneficial when they can cope with problems arising from an illness or disability in ways that are empowering, sustain hope, and affirm their relationships. By providing family function assessments, family therapy, and family interventions [10, 11, 12], nursing service can provide a way to reduce depressive symptoms and enhance the quality of life of patients with PD.

Furthermore, the program to improve quality of life for patients with PD should be designed to develop nursing strategy for social participation and use the community resources [27]. According to data from the NHISS [2], PD patients' economic activity population (40~50s) rate is 9 times higher than dementia. therefore, program to overcome Parkinson's disease by utilizing community resources is required. At the overseas research, an integrated, multidisciplinary care setup involving different healthcare professionals is the mainstay in the management of PD [29]. In Singapore, nurse-led integrated community care program for PD to provide care in community and at patient’s home [30]. In United Kingdom., Parkinson's disease specialist nurse system is being introduced and to reduce hospitalization and outpatient costs to less than 50%. The Netherlands is introducing an advanced system that applies multidisciplinary approach. PD is a complex syndrome of numerous symptoms and mechanisms, because management of it can be managed by a teamwork of various groups of experts to increase efficiency [30]. Therefore, a special interest by the government in PD is needed in both the medical and community.

The present study looked at the association of depression, family function, and quality of life in PD patients, and found that depression has been shown to affect quality of life through family function. However, a limitation of this study was that it was conducted with 157 PD patients who visited only one hospital, thus making it difficult to generalize the results to all patients with the disease. PD is a chronic, progressive neurodegenerative disease, so more cohort studies are needed to establish protective or preventive therapies through follow-up. Another limitation of this study is a lack of specific history regarding the treatments (including drugs and other diseases) for the PD patients.

This study is meaningful in that it conducted a study on clinical patients with PD and confirmed the family function as a factor influencing the quality of life. To improve the efficiency of nursing interventions for PD patients, measures that ultimately enhance the quality of life of patients by improving their adaptability through the evaluation of family function, as well as continuous provision of social and emotional support should be investigated. Since the current research was implemented on PD patients in a local area, caution should be taken in interpreting the results. Future research is recommended comparatively analyses the interceding effect of family function on PD patients with depression. That should be encouraged to reduce depression and improve quality of life by providing family communication, family therapy, and education as interventions to increase family function.