Development and validation of a disease extent index for Wegener's granulomatosis

Aims: The quantitative assessment of disease extent (staging) and activity (grading) in patients with ANCA-associated vasculitides is one prerequisite for the comparison of outcomes in different patient cohorts. We present a validation study of the Disease Extent Index (DEI). Methods: 66 patients wi th Wegener's granulomatosis were examined to assess the validity, reliabili ty and sensitivity to change of the DEL Correlation coefficients were calcu lated to estimate associations between DET and BVAS (Birmingham Vasculitis Activity Score), a previously established activity score, and between DEI a nd serological markers. Results: Among patients with active disease, DEI co rrelated significantly with cANCA titer (r = 0.46), leukocyte count (r = 0. 38) and platelet count (r = 0.53). Among patients in remission, DEI correla ted significantly with cANCA titer (r = 0.61), CRP (r = 0.47) and sIL2R (r = 0.47). Additionally, a high association of DEI and BVAS (r = 0.9) confirm ed a rather high convergent validity. The effect size of DEI equals 2.37 st andard deviation units and indicates a considerable change from active dise ase to remission. Conclusions: The DEI is valid, reliable, easy, quick to p erform and highly reproducible. Although it correlates with some surrogate markers of disease activity and the BVAS, the DEI quantifies different doma ins of the disease than the BVAS and should therefore be used in conjunctio n with the BVAS.