Evolving concepts in classification of systemic vasculitis: where are we and what is the way forward?

The classification of the systemic vasculitides has been controversial for several decades. The Chapel Hill consensus Conference definitions originally developed in 1994, but revised and extended in 2012 are now widely accepted. The American College of Rheumatology (ACR) criteria were first published in 1990, are now generally accepted to be out of date and new criteria are needed. More recently the classical division of the ANCA vasculitides using clinical phenotype has come under scrutiny with evidence from epidemiological, genetic and outcome studies that perhaps these conditions should be classified on the basis of ANCA specificity into PR3-ANCA positive and MPO-ANCA positive groups. The traditional distinction between giant cell arteritis and Takayasu arteritis has been questioned and some recent studies of GCA have included patients with only extra-cranial disease. The Diagnostic and Classification Criteria of Vasculitis study (DCVAS) will provide new validated classification criteria for the systemic vasculitides.