The Sjogren's Syndrome Damage Index - a damage index for use in clinical trials and observational studies in primary Sjogren's syndrome

Objective. To validate a tool for assessment of accumulated damage in patients with Primary SS (PSS). Methods. Of the total 114 patients fulfilling American-European Consensus Group (AECG) criteria for PSS 104 were included in the study and assessed by rheumatologists at T (time) = 0 months and T=12 months. On each occasion, damage and activity data, and autoantibody status were collected. SF-36 and Profile of Fatigue and Discomfort-Sicca Symptoms Inventory (PROFAD-SSI) questionnaires were completed. Cross-sectional analysis of this data was subject to a process of expert validation by 11 ophthalmologists, 14 oral medicine specialists and 8 rheumatologists. Items were removed from the index if >= 50% of respondents recommended exclusion. Statistical validation was performed on remaining items. Spearman's rank analysis was used to investigate associations between damage scores and other disease status measures and Wilcoxon matched-pair analysis to assess sensitivity to change in the damage score. Results. Based on the expert validation, a 29-item damage score was agreed incorporating ocular, oral and systemic domains. Total damage score correlated with disease duration at study entry (r = 0.436; P < 0.001), physical function as measured by SF-36 (r = 0.250, T 0 months; r = 0.261 T = 12 months) and activity as measured by the Sjogren's Systemic Clinical Activity Index (r = 0.213, T = 0 months; r = 0.215, T = 12 months). Ocular damage score correlated with the 'eye dry' domain of PROFAD-SSI (r = 0.228, T = 0 months; r = 0.365, T = 12 months). Other associations not present on both assessments were considered clinically insignificant. On Wilcoxon analysis, the index was sensitive to change over 12 months (z =-3.262; P < 0.01). Conclusion. This study begins validation of a tool for collection of longitudinal damage data in PSS. We recommend further trial in both the experimental and clinical environment.