Efficacy and Safety of Rituximab in the Treatment of Good Prognosis Microscopic Polyangiitis

Inclusion Criteria: 1. Patient (male or female) over 18 year old 2. Patient agree to participate in the study and signed written informed consent 3. Patient with MPA according to the CHCC established in 2012 4. Absence of any poor prognosis factor (modified five factor score (FFS) 1996 = 0) 5. Patient with recent onset or relapse of the disease (\<1 month) defined by BVAS \> 0, who did not received any other treatment than glucocorticoids during last month. For patients with a BVAS\<3, activity of vasculitis (either relapse or new onset) has to be confirmed by the coordinating investigator. One to 3 initial glucocorticoids pulse(s) are allowed. 6. Patient with anti-MPO antibody measured by enzyme - linked immunosorbent assay (ELISA). 7. Negative pregnancy test (serum β-hCG) for women of child-bearing potential and a willingness to use contraceptive measures adequate to prevent the subject or the subject's partner from becoming pregnant during the study and 12 months after stopping therapy Exclusion Criteria: 1. Small-sized vessels vasculitis not associated to anti-MPO antibody or associated with anti-PR3 positivity. 2. Patients with either GPA or EGPA vasculitis according to ACR criteria 3. Patient with a modified FFS 1996 ≥ 1 4. Patient with alveolar hemorrhage requiring mechanical ventilation 5. Patient with previous glucocorticoids treatment \>1 month and \> 10mg/day either for vasculitis or for any other reason. 6. Patient already receiving immunosuppressant or biological agent. Prior treatment with any of the following: * azathioprine, methotrexate, mycophenolate mophetil, mycophenolic acid within 4 weeks before inclusion * alkylant agent such as cyclophosphamide within 6 months before inclusion * anti-TNF inhibitors : infliximab within 8 weeks, adalimumab and etanercept within 2 weeks before inclusion * anti-CD20 therapy within one year before inclusion. 7. Patient with a previous diagnosis of cancer \< 5 years (except for in situ cervical cancer and skin carcinoma with R0 resection) 8. Patient with acute infections or chronic active infections (HIV, hepatitis B or C) 9. Breast feeding woman or woman refusing the use of a contraceptive method for the 18 months' duration of the study 10. Contraindication to treatment (glucocorticoids or rituximab) 11. Unable to receive written informed consent of patient. Patient unable to understand the protocol 12. Patient already in another therapeutic protocol 13. Patient without social security 14. Patient with severe cardiac failure defined as class IV in New York Heart Association classification or severe, uncontrolled cardiac disease. 15. Patients with hypersensitivity to a monoclonal antibody or biological agent. 16. Patients in a severely immunocompromised state.