Classification and management of necrotising vasculitides.

Systemic vasculitides are a heterogeneous group of diseases. Having only a partial understanding of the aetiologies and pathogenetic mechanisms of these disorders explains the difficulties encountered in classifying and treating patients. Nevertheless, some important points have been established. Classification is mainly based on the size of vessels affected and, from the polyarteritis nodosa group, microscopic polyangiitis (MPA) has been separated from classic polyarteritis nodosa (c-PAN). The latter is a rare disease which is, in a small number of cases, the consequence of hepatitis B or C virus (HBV/HCV) infection. In the other cases of c-PAN and in MPA, the aetiology is unknown as for Churg-Strauss syndrome (CSS) and Wegener's granulomatosis (WG). MPA, CSS and WG are mainly antineutrophil cytoplasmic antibodies (ANCA)-related vasculitides. ANCA play a part in the pathogenesis of diseases and are sometimes useful markers for diagnosis and follow-up. Vasculitis treatments should be chosen according to classification, aetiology, pathogenetic mechanisms, severity and predictable outcome. In virus-associated vasculitides, treatment is based on the combination of antiviral agents and symptomatic or immunomodulating therapies. HBV-related PAN and HCV-related cryoglobulinaemia respond to interferon-alpha and to plasma exchange. Responses are excellent in HBV-PAN but usually partial in HCV-cryoglobulinaemia, and relapses occur in the majority of cases. MPA, c-PAN, WG and other vasculitides respond to corticosteroids and cytotoxic agents, mainly cyclophosphamide. Treatment duration and ways of administration can vary from one disease to another. Plasma exchange is not recommended as the first-line treatment. Immunoglobulins and other immunomodulating treatments are indicated in limited cases and their indications necessitate further prospective studies.