This article describes the development of the Sjögren's Systemic Clinical Activity Index (SCAI) for the measurement of systemic disease activity in patients with primary Sjögren's syndrome (PSS).
A pilot tool was developed based on expert consensus and previous published data. One hundred and four patients with PSS were evaluated in a cross-sectional analysis, of whom 65 were reviewed at 3-monthly intervals, using this index, over a 12-month period. Factor analysis was used to evaluate the proposed domain structure. External validation was assessed by comparison with relevant domains of the Profile of Fatigue and Discomfort (PROFAD), Medical Outcomes Study Short Form-36 (SF-36) and The World Health Organization Quality of Life-Bref (WHOQOL-BREF). Sensitivity to change was assessed by comparing SCAI-derived flares with physician-designated disease flare and intention-to-treat analysis. A reliability and repeatability workshop was also held.
Factor analysis supported the proposed domain structure. There were strong correlations between the SCAI fatigue, musculoskeletal and Raynaud's components and the PROFAD fatigue, arthralgia and vascular domains. There was a significant correlation between change in therapy and SCAI-defined flares (P = 0.01). The mean kappa-test results both for reliability of the SCAI and for physician repeatability were 0.71.
This initial evaluation supports the potential for the SCAI as a tool for systemic activity assessment in patients with PSS but additional work is required to assess sensitivity to change in clinical therapeutic trials.