Background Rare chronic childhood vasculitides lack a reliable disease activity assessment tool. With emerging new treatment modalities such a tool has become increasingly essential for both clinical practice and therapeutic trials to reproducibly quantify change in disease state.

Objective To develop and validate a paediatric vasculitis activity assessment tool based on modification of the Birmingham Vasculitis Activity Score (BVASv.3).

Methods A paediatric vasculitis registry was reviewed to identify clinical features missing in the BVASv.3. A modified nominal group technique was used to develop a working version of the Paediatric Vasculitis Activity Score (PVAS). Prospective validation provided tool reliability, reproducibility and responsiveness to change. Training of assessors was done according to the BVAS principles.

Results BVAS items were redefined (n=22) and eight paediatric items added in Cutaneous (n=4), Cardiovascular (n=3) and Abdominal (n=1) sections. The final PVAS has 64 active items in nine categories. The principles of new/worse and persistently active disease were retained as were the overall score and weighting of categories. The median PVAS in 63 children with systemic vasculitis was 4/63 (0–38/63). There was a high interobserver agreement for the overall as well as for subsystem scores (linear-weighted-κ ≥0.87). PVAS correlated with physician's global assessment (p<0.01); treatment decision (p=<0.01) and erythrocyte sedimentation rate (ESR) (p=0.01). In response to treatment, 15/19 patients assessed demonstrated a significant fall in PVAS (p=0.002), with good agreement among assessors for this change.

Conclusions The PVAS validity in children with systemic vasculitis was demonstrated. Like the BVAS, we anticipate that the PVAS will provide a robust tool to objectively define disease activity for clinical trials and future research.