This review focuses on the epidemiological characteristics and etiologies of four primary systemic vasculitides with frequent lung involvement, namely Wegener granulomatosis (WG), microscopic polyangiitis (MPA), Churg-Strauss syndrome (CSS), and Goodpasture syndrome (GPS). Elucidation of the mechanisms underlying these vasculitides with frequent lung involvement is complicated by their rarity, which hampers the undertaking of large-scale studies; difficulties in classification; and their multifaceted clinical presentations, which infer the existence of several etiologic pathways. Notwithstanding, epidemiological research showed some evidence for international, interethnic, and temporal variations of the frequencies of these four vasculitides; led to the identification of several genetic and environmental risk factors; and provided insight on the extent to which genes and environment might contribute to their development. Available data support the concept that WG, MPA, CSS, and GPS have unique and shared risk determinants. Although the precise causes of these vasculitides are not yet fully understood and the development of prevention strategies is out of our reach at present, current knowledge enables the formulation of etiologic hypotheses to provide caregivers and their patients with valuable information on the nature of these rare entities.
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