Cross-cultural adaptation, reliability, and preliminary construct validity of the Japanese version of the Parkinson’s disease pain classification system

• Japanese PD-PCS developed using ISPOR-based cross-cultural adaptation. • Cognitive debriefing finalized a clear and culturally appropriate version. • Pain score showed good intra- and excellent inter-rater reliability. • Scores correlated with pain burden and health-related quality of life. • Measurement error suggests caution for individual longitudinal changes. Pain is a burdensome non-motor symptom of Parkinson’s disease (PD). However, its mechanisms are complex, complicating pain phenotyping. The PD Pain Classification System (PD-PCS) classifies pain mechanisms and their relationship with PD pathology. We developed a Japanese PD-PCS and evaluated its reliability and preliminary construct validity. The PD-PCS was translated and adapted under developer supervision using an ISPOR-guided process. People with PD and chronic pain were recruited from two hospitals (n = 31). Intra- and inter-rater reliability were assessed with intraclass correlation coefficients (ICCs) for the PD-PCS pain score and κ for categorical classifications (95% CIs). The standard error of measurement (SEM) and the smallest detectable change (SDC) were calculated. Construct validity was examined using Spearman’s correlations between the PD-PCS pain score and the Brief Pain Inventory (BPI; average pain, interference). Cognitive debriefing identified wording issues that were resolved through revisions, resulting in the final Japanese version. Participants (n = 31) had a mean age of 70.5 ± 8.3 years, and 16 (51.6%) were men. The intra-rater reliability was good (ICC[3,1] = 0.768, 95% CI, 0.575–0.880; SEM 10.4; SDC_individual 29.0), and the inter-rater reliability was excellent (ICC[2,1] = 0.917, 95% CI, 0.836–0.959; SEM 5.8; SDC_individual 16.0). The agreement between pain mechanisms and PD-related pain classification was substantial to perfect (κ = 0.755–1.000). The PD-PCS pain score correlated with BPI average pain (ρ = 0.744) and interference (ρ = 0.747). The Japanese PD-PCS demonstrated good to excellent reliability and preliminary construct validity, supporting its use in mechanism-informed pain classification in Japanese people with PD.