Validation of the Non-Motor Symptoms Scale for Parkinson's Disease of Persian Version.

OBJECTIVE: We aimed to assess the validity and reliability of the Persian version of the NonMotor Symptoms Scale (NMSS) in Iranian patients with PD.

METHODS: This cross-sectional study was conducted in patients with PD. After the cross-cultural adaptation of the NMSS, the acceptability, reliability, precision, and validity of the Persian NMSS were evaluated. For this purpose, in addition to NMSS, we used the following measures: Scales for Outcomes in Parkinson's Disease (SCOPA)-Autonomic (SCOPA-AUT), SCOPA-Sleep, Beck's Depression Inventory (BDI) questionnaire, Parkinson's Disease Questionnaire-8 questions (PDQ-8), SCOPA-Motor, SCOPA-Psychiatric Complications (SCOPA-PC), SCOPA-Cognition (SCOPA-COG), Mini-Mental State Examination (MMSE), Hoehn and Yahr Staging (H and Y), and Unified Parkinson Disease Rating Scale (UPDRS).

RESULTS: 186 patients were enrolled ( mean age 64.46 ± 9.9 years; disease duration 5.59 ± 3.99 years; 118 (63.4%) male; mean NMSS score 52.01 ± 38.54). Neither the floor effect (2.7%) nor the ceiling effect (0.5%) was seen in NMSS total score. Cronbach's alpha of total NMSS was 0.84. The test-retest reliability was 0.93 for the NMSS total and 0.81-0.96 for domains. The standard error of measurement (SEM) was lower than half of the standard deviation for NMSS total and all domains. NMSS total showed a high correlation with UPDRS I ( r s  = 0.84), UPDRS II ( r s  = 0.58), PDQ-8 ( r s  = 0.61), BDI ( r s  = 0.71), SCOPA-sleep ( r s  = 0.60), and SCOPA AUT ( r s  = 0.66). NMSS has an acceptable discriminative validity based on disease duration and severity of disease according to H and Y staging.

CONCLUSION: The Persian NMSS is a valid and reliable measure for evaluating the burden of nonmotor symptoms in Iranian patients with PD.