Validity of a vasculitis activity index for systemic necrotizing vasculitis

Objective. To establish the validity of an index designed to measure activi ty in systemic necrotizing vasculitis (SNV), Methods, The Vasculitis Activity Index (VAI) was designed to incorporate ap propriately weighted clinical measurements that reflect disease activity in SNV, We performed a pilot study to guide the modification and subsequent t esting of the initial design. The data necessary to calculate the VAI are d irect ratings by a clinical observer of the degree of activity in 9 organ s ystems and 3 indirect measures of vasculitis activity. These data are recor ded on 0-4 visual analog scales. Physician's global assessment (PGA) is use d as the "gold standard" measurement of disease activity, The VAT was valid ated using 2 independent data sets: the questionnaire data set, derived fro m test case histories ("paper cases") sent to 100 practicing rheumatologist s, and the clinic data set, obtained from use of the VAI in 204 regular car e visits of 74 patients with SNV. Results, The VAI correlated highly with the PGA: Pearson's correlation coef ficient R = 0.84 (95% confidence interval [95% CI] 0.80-0.88) for the quest ionnaire data set, and R = 0.92 (95% CI 0.90-0.94) for the clinic data set. The mean of the interobserver coefficients of variation for the test case histories was lower for the VAI than for the PGA (mean difference 0.45; P = 0.002), indicating that the VAI has less interobserver variation than does the PGA, The change in VAI between clinic visits for individual patients c orrelated highly with the change in PGA (R = 0.88, 95% CI = 0.83-0.91), The VAI data collection form requires about 1 minute to complete, including co mputation of the score. Conclusion. The VAI is a valid measure of vasculitis activity that correlat es highly with the PGA, In addition, the VAI has less interobserver variati on than the PGA and has a high level of sensitivity to change over time, Ad ditional testing of the VAI appears warranted.