Pain is a subjective, physiological and psychological experience, influenced by sociocultural factors . In the Parkinson population, pain is an important and frequently reported NMS . In order to investigate the types of pain and its frequency in PD for the Bulgarian patients, we translated and validated the only one PD-specific scale for pain- KPPS. The results of the present study demonstrate that KPPS-BG had good reliability and validity. Cronbach’s α of total scale was 0.75, which indicate good level of internal consistency similar to those reported in the original publication (0.78)  and by Rodríguez-Violante et al. (0.74) , and Soyuer et al. (0.827) .
Almost 80% of our patients reported one or more types of pain. In a recently published cross-sectional study, the authors reported a pain frequency of 88.6% . Silverdale et al.  also using KPPS in patients with early/moderate PD found 85% of participants to experience pain. Slightly lower frequency was revealed in Brazilian cohort (70.3%) . One German study based on a self-developed Parkinson's Disease Pain Questionnaire revealed up to 95 % prevalence of pain in PD patients .
In the present study, the most common type of pain was musculoskeletal (83.7%), which is in line with the results of some previous studies [15, 26], but higher than others . Independent of the use of a PD specific pain assessment tool, this is the most common type of pain described in the literature (frequency range: 40–90%) [7, 11].
Significant differences between the Bulgarian and other populations were observed for item 4 and nocturnal pain domain. Pain deep within the body (item 4) refers to the central pain. It has been reported by 12 % of our patients. These results are in line with other studies where this type of pain was estimated to be present in up to 10% of PD patients . However, they are significantly lower than the results retrieved applying KPPS . Possibly, these differences arise from patient population and socio-cultural peculiarities.
55.0% of patients in the present study suffered from nocturnal pain. This domain shows a large variability among different studies [13, 26] The third most common type of pain was fluctuation-related pain (50.1%), followed by radicular pain (43.4%) and chronic pain (31.0%). 27.1% and 14.3% of the patients, respectively, reported discoloration edema/swelling pain and orofacial pain. Likewise, these two pain categories were least common in other studies [13, 26].
The mean scores of all domains of the KPPS-BG were similar to those observed in the original validation  except for chronic pain (domain 2) where the patients’ score of the original KPPS was significantly higher (3.37 ± 5.53) in comparison with the score of the Bulgarian population.
The mean total score of KPPS-BG was 21.1 ± 17.3 and median 17, which is within the range of those reported by other authors [12, 13].
Item 12. Burning sensation in the mouth demonstrated an item-to-total score correlation below 0.20. Hence, this item was determined as low informative and unreliable for the Bulgarian population.
We have observed a statistical correlation between modified H&Y stage, MDS-UPDRS III and the total score KPPS-BG (Tabale 4). Тhe observed positive correlations reflect the domination of the musculosceletal, fluctuation-related, nocturnal and orofacial pain in the overall score. Similar data was published [12, 13]. Contrariwise, Silverdale et al.  found no correlation between UPDRS III and KPPS most domains. This is probably due to different clinical characteristics: shorter mean disease duration, and UPDRS IV indicated only a low number of PD patients suffering from fluctuations. De Mattos et al.  analysed only 38 patients also with shorter mean disease duration and lower UPDRS III score and reported no significant correlation of UPDRS III and KPPS total score.
The significant difference of KPPS-BG total scores between patients with various motor subtypes of the disease is published also for the Mexican population . Patients with TD subtype were scored lowest.
KPPS-BG detected pain as an initial symptom of the disease in 5.43% of the patients.
6.2% of the participants required further clarification with regard to the words “abnormal” and “involuntary” in item 5. In some cases, additional explanations were required for other items. This allows us to propose the use of the questionnaire and scale in the presence of a medical specialist who is trained to recognize the specific taxonomy of pain in PD.
Due to the lack of consensus on the diagnosis and therapy, pain in PD is still insufficiently managed in routine clinical practice. In the present study, this is reflected by means of the finding that 79.63% of the participants reported one or more types of pain, but only 10.85 % received medications for pain relief.
The current study has some limitations: First, the number of patients with advanced disease (modified H&Y stage 4 and 5) is underrepresented, mainly due to the exclusion criteria. Second, the methodological design of the study is not а case-control, and therefore no control group was included.