Douha Albaroudi

1 INTRODUCTION Antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) is a rare systemic disorder with different phenotypes that can occur at any age and affect 20–25 people per million per year in Europe.1 AAV diseases include microscopic polyangiitis, granulomatous polyangiitis (GPA, formerly “Wegener's granulomatosis”), and eosinophilic granulomatous polyangiitis (EGPA, formerly “Churg-Strauss syndrome”).2 However, up to 10% of patients with small vessel vasculitis have a...