Classification and diagnostic criteria in systemic vasculitis.

Approximately 20 different primary forms of vasculitis are recognized, not all of which have been included in classification schemes or consensus statements regarding nomenclature. A variety of classification schemes have been proposed over the past 50 years, many predicated upon the size of the primary type of vessel involved in a given disease, as well as other considerations that include demographic features, organ tropism, the presence or absence of granulomatous inflammation, the role of immune complexes in pathophysiology and the association of autoantibodies with some forms of vasculitis. All classification schemes to date have had shortcomings owing to the substantial gaps in knowledge about vasculitis, but the American College of Rheumatology criteria for the classification of some forms of vasculitis are useful for the purpose of including patients in research studies. The Chapel Hill Consensus Conference has clarified some existing controversies in nomenclature of the systemic vasculitides. Robust diagnostic criteria for the various forms of vasculitis have, however, remained elusive.