Association Corticosteroid/Azathioprine in Microscopic Polyangiitis/ Polyarteritis Nodosa or Eosinophilic Granulomatosis With Polyangiitis (Churg Strauss Syndrome)

Inclusion Criteria: * male or female patients * aged over 18 years * new diagnosis of microscopic polyangiitis, polyarteritis nodosa or eosinophilic granulomatosis with polyangiitis (Churg Strauss syndrome), satisfying ACR 1990 and/or Chapel Hill Nomenclature criteria (positive biopsy is not mandatory providing those criteria are fulfilled) * with no factor of poor prognosis according to the French five factors score (FFS=0) * at diagnosis or within the first 21 days following initiation of corticosteroids * signed information and consent form * patients covered by Health Insurance * having had a baseline physical examination Exclusion Criteria: * patients with microscopic polyangiitis, polyarteritis nodosa or eosinophilic granulomatosis with polyangiitis (Churg Strauss syndrome) with one or more factor(s) of poor prognosis according to the French five factors score (FFS ≥ 1) * patients with polyarteritis nodosa with ANCA, not satisfying the criteria for microscopic polyangiitis * patients with clinically overt alveolar hemorrhage or respiratory distress syndrome * patient treated with corticosteroids for more than 15 days or already receiving another immunosuppressant * relapsing vasculitis * other vasculitis, especially secondary vasculitides * vasculitis secondary or associated with a viral infection, such as hepatitis B or C virus, or HIV * malignancy * pregnancy and breast feeding,women of child-bearing age not willing or with contra-indication to receive contraceptio…