Validity and Reliability of the Korean Versions of the 9-and 19-Item Wearing-Off Questionnaires in Parkinson’s Disease

Background and Purpose The wearing-off (WO) phenomenon is the most common motor complication in advanced Parkinson’s disease (PD), but its identification remains challenging. The 9-and 19-item Wearing-off Questionnaires (WOQ-9 and WOQ-19) are self-assess-ment tools for motor and nonmotor symptoms that are widely used for WO screening. We produced Korean versions of the WOQ-19 and WOQ-9 (K-WOQ-19 and K-WOQ-9) and investigated their validity and reliability. Methods We used the translation–back translation method to produce K-WOQ-19 and K-WOQ-9, which were self-administered by 124 patients with PD. We conducted in-depth 10-minute interviews for confirming the presence of the WO phenomenon, and then stratified the participants into groups with and without WO. Diagnostic accuracy was assessed by analyzing receiver operating characteristic curves. Concurrent validity was assessed using the Movement Disorder Society–Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) and the Hoehn and Yahr stage with Spearman’s rank correlation analysis. Reliability was assessed based on test–retest Cohen’s kappa (κ) values and intraclass correlation coefficients (ICCs). Results The optimal cutoff scores on the K-WOQ-19 and K-WOQ-9 for WO screening were 4 and 2, respectively. The test–retest ICCs of K-WOQ-19 and K-WOQ-9 were 0.943 and 0.938, respectively. Nineteen of the combined 20 items in K-WOQ-19 and K-WOQ-9 showed mod-erate-to-substantial agreement (κ=0.412–0.771, p<0.001). The scores on the translated scales were significantly correlated with MDS-UPDRS IV scores. Conclusions K-WOQ-19 and K-WOQ-9 are reliable and valid tools for detecting WO, with optimal cutoff scores of 4 and 2, respectively.