What is known about the epidemiology of the vasculitides?

The vasculitides are conditions of unknown aetiology. Until recently, relatively little was known about their incidence and prevalence, but there are now increasing data, especially from Europe. These are conditions of the extremes of age. Kawasaki disease occurs predominately in Asian children, with a peak annual incidence of 90/100 000 children aged under 5 years. Henoch–Schönlein purpura has an incidence of 70/100 000 in those aged 4–7 years and is also more common in Asians. Primary systemic vasculitis has a peak incidence 6/100 000 in those aged 65–74 years. Giant cell arteritis is most common in Caucasians aged over 70 years, with an incidence of 53/100 000. Vasculitis has been associated with malignancy, the association being strongest between haematological malignancies and cutaneous vasculitis. There is occasionally a temporal association; failure to respond appropriately to therapy should prompt a search for malignancy. Lesions suspicious of malignancy should be biopsied even if the diagnosis of vasculitis has been histologically proven.