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

To determine whether a combination of corticosteroids and azathioprine can achieve a higher remission rate and a lower subsequent relapse rate in patients with newly-diagnosed microscopic polyangiitis, polyarteritis nodosa or eosinophilic granulomatosis with polyangiitis (Churg Strauss syndrome) with no poor prognosis factor (FFS=0), and without significantly increasing the rate of adverse events, as compared to corticosteroids alone. The study hypothesis is a reduction of the absolute risk of treatment failure or relapse within the first 24 months following initiation of therapy of least 25%.