By including in this study patients with significant worsening of their lung volumes and / or their DLCO (carbon monoxide diffusing capacity) in the previous year, on the basis of an open retrospective study we recently conducted, we hope to demonstrate that a strategy combining prednisone and intravenous cyclophosphamide therapy is accompanied by an increase in the frequency stabilization / improvement of lung volumes and / or DLCO of patients at 12 months of 15% in the placebo and prednisone cyclophosphamide 50% in cyclophosphamide and prednisone.We also hope to demonstrate significant decrease in the number of patients excluded for failure in the CYC arm as compared to the placebo arm.