The SLICC Damage Index (SDI) is a validated instrument for assessing organ damage in systemic lupus erythematosus (SLE). Trained physicians must complete it, limiting utility where this is impossible.
We developed and pilot-tested a self-assessed organ damage instrument, the Lupus Damage Index Questionnaire (LDIQ), in 37 SLE subjects and 7 physicians. After refinement, 569 English-speaking SLE subjects and 14 rheumatologists from 11 international SLE clinics participated in validation. Subjects and physicians completed instruments separately. We calculated sensitivity, specificity, Spearman correlations and agreement, using the SDI as gold standard. 605 SLE participants in the community-based National Data Bank for Rheumatic Diseases (NDB) study completed the LDIQ and we assessed correlations with outcome and disability measures.
Mean LDIQ score was 3.3 (0-16) and mean SDI score was 1.5 (0-9). LDIQ had a moderately high correlation with SDI (Spearman r=0.50, p<0.001). Specificities of individual LDIQ items were >80%, except for neuropathy. Sensitivities were variable and lowest for damage with <1% prevalence. Agreement between SDI and LDIQ was > 85% for all but neuropathy, reduced renal function, deforming arthritis and alopecia. In the NDB, LDIQ correlated well with comorbidity index (r=0.45), SF-36 physical component scale (0.43), Medical Research Council dyspnea scale (0.40), disability (0.37) and SLE Activity Questionnaire score (0.37).
The LDIQ’s metric properties are good compared to the SDI. It has construct validity and correlations with health assessments similar to the SDI. The LDIQ should allow expansion of SLE research. Its ultimate value will be determined in longitudinal studies.