Development and validation of a Relapsing Polychondritis disease-specific Quality of Life instrument (ERN ReCONNET RP-QoL)

Objectives: Relapsing polychondritis (RP) is a rare, multisystem inflammatory disease characterized by heterogeneous clinical manifestations and a substantial impact on patients' daily functioning and well-being. Health-related quality of life (HR-QoL) in RP remains insufficiently characterized, and no disease-specific measurement tool is available so far. This study aimed to develop and validate the RP-QoL, a multilingual, patient-reported outcome instrument specifically designed to assess HR-QoL in individuals with RP. Methods: The RP-QoL was developed within the European Reference Network ReCONNET using a structured four-step approach: (1) identification of relevant HR-QoL domains through systematic literature review, an international patient survey, and expert consensus; (2) item generation; (3) pilot testing including cognitive debriefing; and (4) comprehensive psychometric validation. Validation analyses included assessment of internal consistency, structural validity, construct validity, convergent validity with the SF-36, and criterion-related validity. Results: Domain identification incorporated input from 274 patients across 22 countries, leading to a 31-item pilot questionnaire with a 28-day recall period and 5-point response scale. Cognitive debriefing confirmed clarity, relevance, and feasibility. Validation in 239 patients from 19 countries (median age 55 years; 80% female) demonstrated excellent internal consistency (Cronbach's α = 0.96). Exploratory factor analysis supported near-unidimensionality, with the first factor explaining 46.6% of variance. RP-QoL scores correlated strongly with disease impact (ρ = -0.62, p< 0.0001) and SF-36 physical (ρ = 0.65) and mental (ρ = 0.55, p< 0.0001) components (both p< 0.0001, p< 0.0001). Discriminative ability was high (AUC = 0.87). Conclusion: The RP-QoL is the first validated, disease-specific HR-QoL instrument for RP, with robust psychometric performance and applicability in both clinical practice and research.