Background/Purpose: The Systemic Lupus International Collaborating Clinics/American College of Rheumatology (ACR) Damage Index (SDI) is a validated instrument for assessing organ damage in systemic lupus erythematosus (SLE). Trained physicians must complete it, thus limiting utility where this is impossible. A self-administered questionnaire, modeled after the SDI, the Lupus Damage Index Questionnaire (LDIQ) has been previously developed and validated. It may allow the ascertainment of this construct in SLE patients followed in the community. The original English version of LDIQ was subsequently translated into Spanish, Portuguese and French. The purpose of the present study was to translate and adapt the LDIQ to Japanese and further investigate its validity and reliability using a prospective observational cohort of SLE patients followed at a single university clinic.

Methods: The English version of the LDIQ was translated, back-translated and culturally adapted to Japanese using standard methodology. Japanese SLE patients who had 4 or more revised ACR criteria for SLE were approached during their outpatient attendance in our university clinic. Some of the hospitalized patients during the study period were also eligible to the study. Patients were asked to complete the LDIQ and other related demographic questionnaires such as Medical Outcomes Study Short Form-36 (SF-36) and physicians were asked to complete the SDI and the SLE Disease Activity Index 2000 (SLEDAI-2K). Patients were prospectively followed for repeat assessment next year.

Results: A total of 250 patients and 30 physicians (all rheumatologists) participated. The acceptability of the LDIQ was high, with most of items having 100% response rate. The distribution of the LDIQ and SDI both skewed to the right. The median LDIQ score was 2 (range 0–12) and the median SDI score was 1 (range 0–9). The LDIQ had a substantial correlation with the SDI (Spearman’s ρ = 0.71, p < 0.001). Cohen's kappa coefficient, a statistical measure of agreement for qualitative items, between the individual SDI and LDIQ items varied between 0.07-1.00. The damage domains of the LDIQ were not associated with each other, which was reflected in low Cronbach’s alpha (0.53). The LDIQ showed poor correlation with the SLEDAI-2K, and mental component summary scores of the SF-36, but had moderate correlation with physical component summary scores of the SF-36 (Spearman’s ρ = -0.08, -0.11, and -0.41, respectively). Twenty-five patients with stable disease were asked to repeat the LDIQ after 2 weeks and the intraclass correlation coefficient was 0.85, which means good test–retest reliability. These figures come from the first year research and the second year gave similar results. The LDIQ demonstrated a good responsiveness: standardized response mean = 0.40 and effect size = 0.32 in patients with worsened SDI.

Conclusion: We have successfully translated, adapted and validated the Japanese version of the LDIQ. There is evidence of acceptable reliability and validity of the Japanese version of the LDIQ among Japanese patients with SLE. Our study provides evidence of the cross-cultural validity of this tool and can be used to assess SLE-related damage among Japanese patients with SLE.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/validity-and-reliability-of-the-lupus-damage-index-questionnaire-ldiq-a-prospective-study/