Validation of the Japanese version of the Lupus Damage Index Questionnaire in a large observational cohort: A two-year prospective study

Abstract

Objectives The Lupus Damage Index Questionnaire (LDIQ) is a validated patient-reported outcome measure to assess accumulated damage in systemic lupus erythematosus (SLE). We aimed to translate it into Japanese and further investigate its validity and reliability. Methods The English version of the LDIQ was translated into Japanese and administered to Japanese patients with SLE (n = 259) at our university clinic. Physicians simultaneously completed the Systemic Lupus International Collaborating Clinics Damage Index (SDI) and SLE Disease Activity Index 2000 (SLEDAI-2K). Patients were prospectively followed for a repeat assessment the following year. Results The median LDIQ score was 2.0. The LDIQ demonstrated substantial correlation with the SDI but poor correlation with the SLEDAI-2K (Spearman’s ρ = 0.75 and −0.08, respectively). These results suggested its convergent and discriminant validity. The LDIQ demonstrated good test-retest reliability (intraclass correlation coefficient = 0.85). When the effect size and standardized response mean for the LDIQ were assessed only in patients who had a change ≥1 in the SDI, they demonstrated a small to moderate responsiveness: 0.43 and 0.59, respectively. Conclusion The Japanese version of the LDIQ had acceptable reliability and validity and its performance was comparable with the original version.