Validation of the Korean-version of the nonmotor symptoms scale for Parkinson's disease

Background and Purpose Non-motor symptoms are common in Parkinson's disease (PD), and are the primary cause of disability in many PD patients. Our aim in this study was to translate the origin non-motor symptoms scale for PD (NMSS), which was written in English, into Korean (K-NMSS), and to evaluate its reliability and validity for use with Korean-speaking patients with PD. Methods In total, 102 patients with PD from 9 movement disorders sections of university teaching hospitals in Korea were enrolled in this study. They were assessed using the K-NMSS, the Unified Parkinson's Disease Rating Scale (UPDRS), the Korean version of the Mini-Mental Status Examination (K-MMSE), the Korean version of the Montgomery-Asberg Depression Rating Scale (K-MADS), the Epworth Sleepiness Scale (ESS), and Parkinson's Disease Questionnaire 39 (PDQ39). Test-retest reliability was assessed over a time interval of 10-14 days in all but one patient. Results The K-NMSS was administered to 102 patients with PD. The internal consistency and reliability of this tool was 0.742 (mean Cronbach's α-coefficient). The test-retest correlation reliability was 0.941 (Guttman split-half coefficient). There was a moderate correlation between the total K-NMSS score and the scores for UPDRS part I [Spearman's rank correlation coefficient, (rS)=0.521, p<0.001] and UPDRS part II (rS=0.464, p=0.001), but there was only a weak correlation between the total K-NMSS score and the UPDRS part III score (rS=0.288, p=0.003). The total K-NMSS score was significantly correlated with the K-MADS (rS=0.594, p<0.001), K-MMSE (rS=-0.291, p=0.003), and ESS (rS=0.348, p<0.001). The total K-NMSS score was also significantly and positively correlated with the PDQ39 score (rS=0.814, p<0.001). Conclusions The K-NMSS exhibited good reliability and validity for the assessment of non-motor symptoms in Korean PD patients.