This study is a comprehensive exploration of the association of total number of non-motor symptoms and health-related quality of life for PD patients quantitatively using a large smartphone-based way to capture data in the UK. For patients with PD, NMS have been considered as a significant content, and appropriate therapy can considerably improve quality of life [25]. Many researchers have explored how some items of the NMS independently have effect on the health-related quality of life, such as depression, sleep, mood and attention [13, 26], less researchers focused on the association between the total number of NMS and health-related quality of life through PDQ-8. This study explored the association between total number of NMS and health-related quality of life for PD patients and found that the higher the sum of NMS-30 questions was, the worse the health-related quality of life became. The NMS could be related to degeneration of different brain structures, may reduce the PD patients’ health-related quality of life, and may cause severe disability and shorten life expectancy, which should be considered in the treatment plan [7].
Our study reveals that almost every patient with PD presented with more than one symptom. The relative NMS occurrence, as evaluated by NMS-30, is consistent with several other studies, showing sleep (difficulty getting to sleep), mood/cognition (sad or blue), memory/attention and urination (urgency, getting up regularly at night to pass urine) as the most prevalent symptoms both for PD patients with and without limited ability to work [27–29]. However, the absolute occurrence of the most frequent symptoms are lower than Paulo Bugalho’s study (Sleep/fatigue, affect/cognition, attention/memory were all above 80%) [30], but higher than other studies [28, 29], in which above 60% are rare, while in our study “Difficulty getting to sleep” is 70.90% for patients with limited ability to work and is 59.81% for patients without limited ability to work; “Urgency to pass urine makes you rush to the toilet” is 77.40% for patients with limited ability to work and is 62.45% for patients without limited ability to work, further investigation is needed to verify.
Depression is reported to be one of the common complication of PD ranging in prevalence between 2.7% and 70% but is under self-reported[31]. Some studies showed depression can occur before the onset of PD, and it may have a significant effect on the patient’s quality of life [31–34]. In our study, depression (Feeling sad low or blue) is one of the most prevalent symptoms both for patients with and without limited ability to work. Depression prior PD diagnosis was also a potential determinant of worse quality of life.
Age and education were found to be correlated with health-related quality of life of PD patients significantly. It is well known that age is the greatest risk factor for the development of PD. A previous study showed age-specific incidence rates of PD increased sharply beginning at age 60 years and peaking after 80 years [35]. In our study, patients aged 60–69 years had better quality of life than patients aged less than 59 years, which is inconsistent with previous research, further investigation is needed to verify. Compared with patients educated up to 16 years old, patients educated up to 18 years old is a potential determinant of better quality of life, which is accordance with the conclusion that higher education is associated with better health-related quality of life [36, 37].
Limitations
Our study presents some limitations. Firstly, due to the limitations of question setting in the questionnaire, some potential factors that affect health-related quality of life were not controlled for in this study, such as individual exercise, occupation, income level or marital status. Secondly, this study conducted a brief question on whether patients’ motor symptoms limited their ability to work and divided the characteristic of motor symptoms into with or without limited ability to work, but lacked a detailed evaluation of Parkinson’s patients’ motor symptoms. More detailed study are needed to verify the association between non-motor symptoms and health-related quality of life for patients with Parkinson’s disease after controlling for their motor symptoms. Thirdly, this is a quantitative study that reports the association between non-motor symptoms of PD patients and health-related quality of life. In the future, more qualitative research will be needed to verify the association.