Characterization of pain in patients with Parkinson ’ s disease : a descriptive cross-sectional study

Parkinson's disease affects the central nervous system, causing dysfunctional dopamine production. This directly affects the motor system, leading to the loss of voluntary movements, joint stiffness, limb tremors, and imbalance. Palliative treatments are applied to alleviate symptoms of the disease and improve quality of life. Considering functional changes and symptoms that are generated by Parkinson's disease, pain is also a debilitating factor that can severely affect the individual. The present study investigated the mean age, duration of involvement, body locus incidence, and interference with quality of life by pain in patients with Parkinson's disease. We applied a one-dimensional, subjective, and qualitative Visual Analog Scale and the multidimensional and interpretative Wisconsin Brief Pain Inventory. The study was conducted with 36 participants of both genders (mean age: 65.5 years for men and 72.0 years for women). The incidence of pain was detected in 87.5% of the participants. We found that pain occurred more frequently in the upper limbs and interfered with the performance of general activities. Treatment by a multidisciplinary team in all dimensions of the disease is needed to alleviate patients’ pain and consequently improve their quality of life.


Introduction
Parkinson's disease is a chronic degenerative disease that causes central nervous system degeneration, with neuronal loss in the substantia nigra that leads to changes in the region of basal nuclei. Although studies indicate factors that accelerate the emergence of Parkinson's disease, such as aging, its origin has not yet been discovered (Alexander, 2004). This disease is characterized by postural changes that lead to changes in gait and balance, and patients may show muscle and cognitive deficits, such as alienation and depression. These changes can progress to cardiac and respiratory dysfunction and many classic signs and symptoms, such as stiffness, bradykinesia, facial masking, postural changes, and resting tremor (Samii et al., 2004;Bloem et al., 2001). All of these bodily changes result in susceptibility to falls, functional limitations, and other disabilities. Parkinson's disease can also cause difficulties in performing normal daily activities that can become progressively worse, causing permanent disabilities in more advanced phases of the disease. Patients can also experience pain, which can be observed in early stages and limits quality of life (Navarro-Peternella and Marcon, 2012). Thus, individuals with Parkinson's disease acquire motor and physical problems and experience psychological and social changes (Grover et al., 2010 inhibitors, catechol-O-methyltransferase inhibitors, and anticholinergic and anti-glutamatergic drugs. Over the past two decades, patient care and palliative care have been highlighted more broadly in the health field, with the goal of controlling and relieving stressful symptoms, including pain (Raza et al., 2019).
Although drug therapy is essential, physiotherapy also plays an important role in the treatment of Parkinson's disease. For example, physical exercises that are specific to certain stages of the disease can maintain muscle activity and consequently preserve patients' independence (Lim et al., 2017). Physical therapists have been encouraged to seek a better understanding of the harmful processes that are associated with pain and develop alternative Research, Society and Development, v. 9, n. 10, e6069109057, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.9057 5 techniques for its treatment. Standards for pain measurement are needed to help physiotherapists to evaluate the disease, type of pain, degree of functional limitation, and impact on the patient. Therefore, it is essential to identify and classify specific types of pain and their impact on the quality of life of patients who are affected by Parkinson's disease so that complementary therapies can be applied (Redecker et al., 2014).
Among several pain and quality of life assessment instruments, two can be safely used for Parkinson's disease patients. One such instrument is the Visual Analog Scale, which is a one-dimensional form that is used to measure pain at a specific moment in time. The present study evaluated the degree of pain and its influence on daily activities in Parkinson's disease patients who were receiving palliative care. For measurement purposes, the patients' pain conditions were assessed using a one-dimensional, subjective, and qualitative Visual Analog Scale and the multidimensional and interpretative Wisconsin Brief Pain Inventory. To carry out this research, internationally validated protocols were followed, and important rules of scientific methodology were followed, as proposed by Pereira et al. (2018).

Experimental design
A descriptive cross-sectional survey was performed using face-to-face interviews of patients with Parkinson's disease who were receiving palliative care under supervision of the  Research, Society and Development, v. 9, n. 10, e6069109057, 2020 (CC BY 4.

Subjects
Thirty-two patients of both sexes were randomly selected from medical records of healthcare facilities in the municipality of Dois Vizinhos, Paraná, Brazil, who voluntarily agreed to participate in the study. Patients were included if they were able to provide informed consent, had a proven medical diagnosis of Parkinson's disease, were registered in public health programs that treated the disease, were over 18 years old and under 85 years old, received conservative medical treatment, and had sufficient cognitive faculties to answer the questionnaires. Patients were excluded if they had diagnoses of other neurological or psychiatric diseases, had visual or auditory deficits that prevented completion of the instruments, or were unable to provide consent.

Study instruments
Basic demographic data for each patient, clinical data, daily living activities, and eligibility criteria were gathered. Practical training of the examiners was performed to minimize the occurrence of errors that could reduce reliability of the instruments. The evaluation of all participants followed the same order and were made at the patients' homes by a physical therapist. Pain was measured quantitatively using a Visual Analog Scale to determine the incidence and degree of pain involvement. The Wisconsin Brief Pain Inventory was used to assess the locus of pain and the intensity and type of pain.

Visual Analog Scale
Pain intensity was evaluated using a VAS. The patients were asked to express their level of pain by making a mark on a 10 cm horizontal line. A score of 0 on the extreme left indicated no pain. A score of 10 on the extreme right indicated unbearable pain. The scores allowed the categorization of pain intensity: mild pain (0-4.4), moderate pain (4.5-7.4), and severe pain (7.5-10; Gallagher, 2001).

Wisconsin Brief Pain Inventory
The patients were interviewed and underwent application of the Wisconsin Brief Pain Inventory (Ferreira et al., 2011). This instrument consists of nine items that measure pain, Development, v. 9, n. 10, e6069109057, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.9057 7 locations on the body that are affected by pain, pain intensity (sensory dimension), medications and other treatments, improvements that are caused by medications and other treatments, and interference with life by pain (reactive dimension).

Statistical analysis
Initially, the Shapiro-Wilk normality test was performed, which indicated that the data did not fit a Gaussian distribution model. The data are expressed as medians and interquartile ranges (IQRs). For comparisons between sexes and numerical scores on the Wisconsin Brief Pain Inventory, the Mann-Whitney U test was used. The 2 test was used to identify associations between the worst pain scores in the last 24 h (Wisconsin Brief Pain Inventory) and dependent variables (time of disease evolution, treatment, marital status, quality of life, and pain location), with Fisher's exact test and Yates' correction when the expected value was less than 5. Spearman's correlations between Wisconsin Brief Pain Inventory and Visual Analog Scale scores were also assessed. The analyses were performed using SPSS 25.0 software. The level of significance was p ≤ 0.05.

Results
Age, the time of Parkinson's disease evolution, pain intensity scores based on the Wisconsin Brief Pain Inventory, and interference with quality of life by pain in 37 participants are shown in Table 1. The median data and respective IQRs of the analyzed variables were not significantly different between men and women (p ≥ 0.05). For the observed scores of worst pain in the last 24 h for both sexes (median = 7, IQR = 2-5.5, and median = 7, IQR = 3-8, for men and women, respectively) and pain interference scores at work for men (median = 8, were worrisome, given that the instrument's parameters denote a score of 0 for no pain and 10 for greatest pain imaginable or pain interference.