Psychosocial dimensions of pain in axial spondyloarthritis: Construct validity and responsiveness of the multidimensional pain inventory (MPI).

BACKGROUND: The West Haven-Yale Multidimensional Pain Inventory (MPI) assesses multidimensional aspects of chronic pain across five domains: pain severity, pain-related life interference, affective distress, social support, and life control. In axial spondyloarthritis (axSpA), pain frequently extends beyond inflammation and involves nociplastic and central sensitization mechanisms. OBJECTIVES: To assess the construct validity of the psychosocial section of the MPI (part 1) by examining its correlations with measures included in the Assessment of SpondyloArthritis International Society (ASAS) core domain set. DESIGN: Observational post hoc analysis of a multicenter randomized controlled trial. METHODS: Patients with axSpA and a pain score ≥4 (0-10) were prospectively enrolled. In addition to the five MPI domains, measures of disease activity, patient global assessment (PtGA), physical function (BASFI), health-related quality of life, fatigue, total back pain, morning stiffness, and spinal mobility (BASMI) were assessed. RESULTS: A total of 136 patients were included. Pain-related life interference correlated strongly with disease activity, BASFI, health-related quality of life, fatigue, and total back pain, and moderately with PtGA, mental component score (MCS), morning stiffness, and BASMI. Pain severity correlated strongly with disease activity and total back pain. Affective distress correlated strongly with MCS. Social support showed only weak associations, while life control correlated strongly with MCS but weakly with other domains. CONCLUSION: The MPI-part 1 demonstrated construct validity in axSpA. Its domains capture psychosocial pain aspects like social support not reflected in current ASAS core domain set, supporting its potential value for personalized pain assessment and research in axSpA. REGISTRATION: German Clinical Trials Register (DRKS00037509).