Epidemiology of the vasculitides.

The epidemiology of systemic vasculitis is becoming increasingly well understood. Giant cell arteritis is the commonest type of vasculitis with an incidence that is highest in populations of Scandinavian descent, where the annual incidence reaches 15 to 35/100,000 aged > 50 years. Takayasu's arteritis has a relatively uniform global incidence of one to two/million. The ANCA-associated vasculitides have an overall incidence of 20/million with a peak age of onset at 65 to 74 years. Wegener's granulomatosis appears to be more common in northern Europe compared with microscopic polyangiitis, which seems to be more common in southern Europe. Henoch-Schönlein purpura is the commonest form of childhood vasculitis in the West with an incidence of 20/100,000 aged < 17 years, but it is much rarer in adults (13/million). Kawasaki disease is commonest in the childhood population of southeast Asia; in Japan the incidence is 500/million aged < 5 years, 50% of cases occur in those aged < 2 years. Behçet's disease occurs along the Silk Road and in the Mediterranean littoral with a prevalence in Turkey of 380/100,000. The various types of vasculitis have very different geographical and ethnic distributions, which provide clues to the pathogenesis.