Critical appraisal of classification criteria for vasculitides.

The vasculitides are a group of protean diseases, some of which are caused by conditions including infections, other autoimmune diseases, or neoplasias. They are a challenge to the clinician, in terms of both diagnosis and therapy. No diagnostic criteria exist, although a multinational effort to develop them is in progress. However, many classification criteria have been proposed, and these have served as diagnostic surrogates and have made it possible to discriminate between many, although not all, of the vasculitides, mainly for epidemiological and therapeutic trial design purposes. In this review we recognise the difficulties of defining such criteria, but at the same time attempt to provide a critical overview of efforts to do so. The increasing knowledge regarding many of these diseases makes us confident that the time will come when their aetiology, or at least their main pathogenic features, is known, rendering proposed classification criteria obsolete.