Loïc Guillevin, Christian Pagnoux, Philippe Guilpain

Vasculitides are defined by inflammation of blood vessel walls leading to vascular stenosis or occlusion, with various degrees of fibrinoid necrosis of the media and inflammatory infiltration, mainly neutrophilic and sometimes granulomatous. Various classifications of the vasculitides have been proposed. The classifications used most today are the 1990 American College of Rheumatology classification and the Chapel Hill nomenclature, published in 1994 . Only the latter distinguished between polyarteritis nodosa and microscopic polyangiitis and stressed the importance of antineutrophil cytoplasm autoantibodies (ANCA). In practice, primary systemic vasculitides are classified according to their clinical presentations, their precise histological features, and the size of the predominantly affected vessels. Some small-vessel vasculitides are associated with the presence of ANCA: 90% of patients with systemic Wegener's granulomatosis (mainly ANCA with cytoplasm labeling on indirect immunofluorescence and proteinase 3 specificity), 80% of the subjects with microscopic polyangiitis (mostly pANCA with myeloperoxidase specificity), and more than one third of those with Churg-Strauss syndrome (mostly pANCA).