Parkinson’s Disease (PD) is the world’s second most common neurodegenerative disease, and affects over 10 million people worldwide [1, 2]. Apart from resting tremor, slowness of movement, stiffness in muscle tone, and imbalance of body posture, PD is frequently accompanied by depression, dementia, swallowing difficulty, and speech and voice disorders [3-5]. Hypokinetic dysarthria, a speech disorder that commonly presents in patients with PD, often results in limitation in their social interactions [6, 7]. PD affects many aspects of patients’ lives and since this disease is progressive, it is important to maintain functional abilities related to independent living when providing rehabilitation services [8-10] in order to maintain their quality of life [11, 12] and reduce the burden on caregivers [13].

Quality of life is defined as an individual’s perception of their experiences in life [14]. It also reflects the degree of challenges that one faces in life [15], including social functions, emotional, physical, and mental conditions. Quality of life has been used as a clinical outcome measure for service delivery in different disorders, including PD [5, 16]. Some of the commonly used tools that quantify quality of life in PD are the Parkinson’s Disease Questionnaire (PDQ-39), Parkinson’s Disease Questionnaire Short Form (PDQ-8), Parkinson’s Impact Scale (PIMS), Parkinson’s Disease Quality of Life Questionnaire (PDQL), and Scales for Outcomes in Parkinson’s Disease–Psychosocial (SCOPAPS) [17]. Among these, the PDQ-39 is commonly used to measure one’s experiences of the impact of PD on life. It is widely used in determining treatment outcomes and when reviewing the overall impact of PD [18]. It consists of 39 items and measures eight dimensions of quality of life relating to PD (i.e., mobility, activities of daily living, emotional, stigma, social support, cognitions, communication, and bodily discomfort).

Using the PDQ-39, PD patients reported higher scores (indicates poorer experience) in the mobility dimension. This indicates that PD is severely affecting the patients’ mobility, and the rank is followed by activities of daily living dimension or bodily discomfort [7, 19, 20]. When comparing quality of life between people with PD and the general population, Schrag and colleagues (2000) found that individuals with PD showed greatest impairment in the areas related to physical and social functioning. For instance, the core features of PD such as slowness of movement and muscle stiffness could have limited their daily physical function in feeding themselves, doing household chores, etc. and thus, further affected their social interactions with others when physical movement including speech are greatly impaired [21]. However, both those with PD and the general population showed similar scores in emotional adjustment, indicating that PD interferes with various aspects of quality of life, particularly those related to physical and social functioning. By understanding an individual’s quality of life, clinicians could determine the difficulties experienced by individuals. Therefore, the PDQ-39 could be used to better understand the person's perspective of goals and disability when planning a treatment protocol that promotes the social, emotional, and physical well-being of individuals with PD [22]. While quality of life helps evaluate an individual’s life experiences, the individual’s satisfaction about life may be measured by the life satisfaction scale, a subjective measure that focuses on one’s perspectives on life as a whole [23]. A psychological study on the elderly showed that better life satisfaction could reduce the risk of mortality by 18% [24]. To date, there is no research which examines the life satisfaction levels of people with PD; their satisfaction towards life with PD is yet to be defined. It is difficult to improve life’s satisfaction when the relationship between life’s satisfaction and quality of life is not explained.

Apart from quality of life and life satisfaction level, communication is another important aspect of life. Communication is essential for social interaction and is strongly associated with the quality of life [25]. It is crucial to understand the communicative difficulties experienced by individuals, and to develop effective interventions to achieve the rehabilitative goals of improving the quality of life [11, 22]. When treating patients with a progressive disorder such as PD, dealing solely with physical function is insufficient. Clinicians should take into account various life domains, including social interaction and communication factors when working with PD patients. According to the American Speech-Language-Hearing Association (2016), speech-language pathologists should address patients’ communication skills in order to increase their quality of life. However, quality of life is often overlooked by speech-language pathologists due to the absence of a conceptual relationship between communication and quality of life [25]. In fact, speech and language changes in PD have negative impacts upon individuals and their family lives before the frank impairments of intelligibility are apparent [26]. One common way to assess patients’ speech intelligibility is by using a self-rating scale. Self-rating of speech performance was designed to measure an individual’s perception of his or her speech performance to measure the outcomes of speech treatment such as stuttering and motor speech disorders [27-29].

Although speech-language pathologists have been practicing in Malaysia for over 20 years, no research has been conducted to determine the quality of life and communication component of individuals with PD [30]. Hence, this research had three goals. First, to compare the quality of life of individuals with PD with healthy controls. Second, to determine if the communication component of the Parkinson’s Disease Questionnaire (PDQ-39) differed between these two groups. Third, to evaluate the relationship between QOL, age, gender, duration of disease, Self-Rated Speech Scale (SRSS), and Life Satisfaction Scale (LSS) for the PD group.

To our knowledge, this is the first study evaluating QOL and subjective self-rated speech intelligibility in patients with PD in comparison with a control group in Malaysia. Consistent with the previous research, our findings showed that the PD group scored higher in PDSI scores than the control group [21, 34]. Individuals with PD had worse QOL scores in all dimensions than the control population, indicating that individuals with PD tend to have a lower quality of life than controls. Although PD and control groups had significant differences in mobility, activities of daily living, emotional, stigma, cognition, communication, and bodily discomfort scores as reported in the PDQ-39, such group differences were not observed in the social support dimension. This result might be due to the sample recruitment location, given that 96% of the participants were recruited from a support group. The present data indicate that participation in a support group provides benefits in improving their social support. Indeed, previous studies have shown that members of a PD support group would have greater acceptance of the disease and cope better with difficulties in life than non-members [35-37]. Further research is warranted to determine whether social support is more positive for those who participated in the self-help group than those who do not.

In PD, speech impairment often leads to communication difficulties and affect participation in life, and quality of life [7]. This was supported by our finding that individuals with PD struggle with more communication issues than the control group. Additionally, PD participants who have a better perception of their speech intelligibility (i.e., lower scores on the SRSS) tend to have a better quality of life and vice versa. This suggests that the feeling of being “able to communicate” is important in maintaining social relationships with one’s family and relatives, and “feeling accepted by others” is important because it provides patients with feelings of acceptance and assurance. Again, communication deficits appear to be a significant concern in individuals with PD because they might limit their social relationships [20, 38]. As such, poor speech intelligibility in individuals with PD could lead to social exclusion, which can negatively affect their health and well-being due to increasing allostatic load [39]. The allostatic load theory aims to explain the physiological mechanisms that lead from various stressors experienced over the lifespan [40]. However, some participants also reported that communication does not affect their overall quality of life. One possibility is that this claim might result from lack of clarity in the SRSS scale. More specifically, some participants reported that they were unsure how to answer this question. The research team is aware that PD patients are seldom asked to judge their speech in clinical settings. For all of our participants, this appears to be the first time they had been asked to judge their speech using the SRSS scale. Given that communication difficulties affect quality of life, clinicians should take into account the need to educate patients to rate their speech, particularly when considering their speech intelligibility expectations. Future studies in this population should include both subjective and objective speech measurements that provide more clinical data assessing the relationship between speech intelligibility and quality of life. This could guide clinicians to better understand their clients’ needs when providing speech treatment to increase their quality of life and enhance good practice standards, as required by the Speech Therapist’s professional’s guidelines [41].

In general, age and gender showed no significant correlation with the PDSI score, indicating that the PDQ-39 is an age- and gender-free survey. In addition, the non-significant correlation between the duration of disease and the PDSI score implies that the PDQ-39 is a quality of life measurement for PD patients regardless of the duration of the patient having the disease. However, this was not the case for life satisfaction levels. Respondents from this study reported a moderate correlation between the LSS and PDSI scores, indicating that life satisfaction could affect their quality of life. Additionally, when asked to fill in the life-satisfaction scale, approximately 80% of the participants commented that their life-satisfaction level is greatly affected by their medication. For instance, patients with inconsistent medication effects would report lower life-satisfaction scales than those who are more consistently responsive to drugs. It seems that medication effects significantly affect these patients’ levels of quality of life [42].

Two limitations are relevant to the present study. First, PD participants were instructed to fill in this survey based on their impression of the ‘medication ON’ stage. Results reported in this current study do not reflect their quality of life levels at the ‘medication OFF’ stage. Most of the participants commented that they have different performances depending on whether medication is ON or OFF state. Future studies should compare the QOL of PD participants during both medications ON and OFF states to determine whether medication stage affects an individual’s overall quality of life. Further analysis, such as the Bayes methods, could be conducted to expand the scope of our research question to better understand the factors that could affect quality of life levels at medication ON vs OFF stages in these patients [43, 44].

Second, some participants commented that two items from the PDQ-39 (item 2- “Had difficulty looking after your home, e.g. DIY (Do-It-Yourself), housework, cooking?”) and (item 15- “Had difficulty cutting up your food?”) might not be culturally appropriate. In Malaysian culture, the term “DIY” is not in common daily usage, particularly by the elderly. Additionally, the term “look after” does not typically include cooking or housework; it means to keep an eye on the home from robbery or fire by most of the participants. For item 15, “cutting up food” using fork and knife is not part of Malaysian culture. Malays and Indians use their right hands without utensils during meals, while the Chinese use chopsticks or spoons and forks. Most of the participants commented that they do not need to cut their food with a knife while eating. A slight modification of these two items to become more culturally appropriate would also increase clarity in future studies.

The present study shows that PD patients have a lower quality of life than the general public, and demonstrated that PD support groups could help to improve social support. This study also indicates that the PDQ-39 is an age- and gender-free survey. In addition, the duration of having PD does not affect quality of life as measured by the PDQ-39 in the current sample. It was also found that medication responsiveness may be one factor that influences life satisfaction and quality of life. Given that SRSS and quality of life scores are moderately correlated, identifying patients’ perceptions of their speech intelligibility could help clinicians to better understand patients’ needs during speech therapy. Future studies should examine the effects of medication, SRSS, and LSS on the quality of life of PD patients to provide a high quality of service delivery.