Psychometric Properties of the Multidimensional Pain Inventory: Japanese Language Version (MPI-J)

Background: Many self-report scales have been developed. Among them, are those clinically useful scales for quantifying chronic pain (such as the Numeric Rating Scale), which are useful for determining the effectiveness of treatment, and multifaceted and comprehensive pain assessment scales that are used to determine therapeutic strategies. The representative measure of the latter is the West Haven Yale Multidimensional Pain Inventory (WHY-MPI), which constitutes a system for classifying patients with chronic pain termed the multiaxial assessment of pain (MAP), proposed by Turk and Rudy. Objectives: This study aimed to evaluate the psychometric characteristics of the Japanese version of the MPI (MPI-J). Study Design: Cross-sectional study. Setting: Specialized Pain Management Center at Hoshi General Hospital. Methods: We assessed the reliability and validity of the MPI-J in 100 Japanese patients with chronic musculoskeletal pain. Internal consistency was assessed using Cronbach's a coefficient for reliability. Regarding the convergent and discriminant validities, we examined the intercorrelations among the 9 subscales of the MPI-J, and the MPI-J intercorrelation was compared with the other language versions. Regarding criterion-related validity, the correlation coefficients between the MPI-J and some variables such as pain, mood, and quality of life were examined. Results: The subscales of the MPI-J demonstrated acceptable reliability coefficients (0.75-0.95). Regarding the intercorrelation between the MPI-J variables and criterion-related validity, previous study results of versions in other languages were also confirmed in this study. Limitations: This study has some limitations. First, in this study, the analyses performed did not take into consideration the presence or absence of a diagnosis of neuropathic pain. Second, our study sample size was small, and the subjects were intractable cases referred to our pain center due to difficulty in treatment at many medical institutions. Therefore, the results of this study should be interpreted as a survey at a specialized medical institution where many intractable cases are referred. Third, it should be noted that a stronger association between the items of each scale may have been shown because the study was conducted on intractable cases than if it was conducted in general outpatient clinics. Conclusion: The study findings support the applicability of the MPI-J as a clinical assessment scale in Japanese patients with chronic musculoskeletal pain.