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

Objective: 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.

Conclusions: The Japanese version of the LDIQ had acceptable reliability and validity and its performance was comparable with the original version.