Epidemiological features of Wegener's granulomatosis and microscopic polyangiitis: two diseases or one 'anti-neutrophil cytoplasm antibodies-associated vasculitis' entity?

Because of their multiple overlapping clinical characteristics, Wegener's granulomatosis (WG) and microscopic polyangiitis (MPA) have increasingly been conceptualized as different expressions of a unique anti-neutrophil cytoplasm antibodies (ANCA)-associated vasculitis (AAV) disease spectrum. However, this continuum theory remains hindered by uncertainty surrounding a potentially common etiology. This review sheds light on our current understanding of the epidemiology of WG and MPA with the aim of weighing the evidence supporting whether or not these two vasculitis forms are distinct diseases. At present, some epidemiological evidence exists that WG and MPA might correspond to mere variants of a single AAV entity.