[Approach to the study of vasculitides: general aspects and classification]

Since etiology and pathogenesis of most systemic and/or isolated vasculitides are unknown, any attempt to make a rational classification of these entities is far from being perfect. Vasculitis may be a primary disease or it may be associated with connective tissue diseases, infectious diseases, neoplasms, drug assumption, allograft rejection and so on. As secondary vasculitides constitute the majority of cases, diagnosis of primary vasculitis is made by exclusion. At the present time, the 1993 Chapel Hill Consensus Conference on Nomenclature of Primary Vasculitides provides a useful guide to clinician and pathologist for evaluating a patient with an idiopathic form of vasculitis. This classification is based on the predominant size of vessels affected and describes the main clinico-pathologic features of the various clearly defined types of systemic vasculitis. Though it suffers from omissions and contradictions, in routine practice it is of great help to distinguish diseases in this intriguing chapter of pathology.