An update on the epidemiology of ANCA-associated vasculitis.

ANCA-associated vasculitis (AAV) includes granulomatosis with polyangiitis, microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis. Epidemiological studies in AAV are important in understanding possible aetiologic mechanisms and facilitating healthcare planning. However, epidemiological studies present a number of challenges including clear definition of cases differentiated from other clinical disorders, and identification of cases due to the rarity of AAV. The aim of this review is to summarize different aspects on the epidemiology of ANCA-associated vasculitis from different geographical areas throughout the world. During the past three decades, development of classification criteria worldwide, including the ACR classification of 1990, the Chapel Hill consensus definitions updated in 2012 and the EMA algorithm has facilitated epidemiology studies in AAV. The available epidemiological studies reported in AAV suggest that incidence and prevalence may have increased over the past 30 years. Possible explanations for this increase may be a genuine increase in incidence, the evolution of classification criteria and the definition, and availability and wider use of ANCA serology to aid diagnosis, and greater physician awareness through education. The age-specific incidence for the whole group of AAV showed a clear increase with age. However, there has been a clear shift in the peak age at onset towards a higher age during the last 20-30 years. In addition, variation in incidence of AAV between men and women has been clearly evident in a number of epidemiological studies.