Comparison of a Strategy Based on Clinico-biological Monitoring Versus Pre-emptive Rituximab Treatment in Cases of ANCA Reappearance in Granulomatosis With Polyangiitis and Microscopic Polyangiitis.

Inclusion Criteria: * Adult patients aged ≥ 18 years * Diagnosis of granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA) according to the 2022 American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) classification criteria * Maintenance treatment with rituximab for at least 18 months, administered as follows: a 500 mg infusion on day 1 (with an optional repeat dose on day 15), followed by 500 mg infusions every 6 months for a total of 4 to 5 doses * Patient in complete remission, defined as a Birmingham Vasculitis Activity Score (BVAS) of 0 at the time of randomization * ANCA repositivity (confirmed by antigen-specific testing) within the 3 months prior to randomization * Ability to provide written informed consent prior to participation * Affiliation to a national health insurance or social security scheme Exclusion Criteria: * Diagnosis of any vasculitis other than GPA or MPA * Active disease relapse, defined as BVAS \> 0 * Acute active infection requiring hospitalization or intravenous anti-infective therapy within 4 weeks prior to screening, or oral anti-infective treatment within 2 weeks prior to screening * History of deep tissue infections (e.g., fasciitis, abscess, osteomyelitis, septic arthritis) within 12 months prior to inclusion * History of severe, chronic, or recurrent infections, or any underlying condition predisposing the patient to serious infections * Administration of a live vaccine within 4 weeks prior to study inclusion * Active malignancy or history of hematologic malignancy within the past 5 years, except for localized prostate cancer or basal cell carcinoma of the skin * Presence of systemic diseases for which the study treatments may have unpredictable or inappropriate consequences * History of severe allergic or anaphylactic reactions, or known hypersensitivity to humanized or murine monoclonal antibodies and/or corticosteroids * Known hypersensitivity to any monoclonal antibody or biologic agent * Patients previously deemed non-responders or failures to rituximab therapy * Suspicion of poor adherence to treatment or anticipated inability or refusal to comply with the required follow-up visits and procedures * Inability or refusal to provide written informed consent Pregnant or breastfeeding women. Women of childbearing potential must use effective contraception during the study and for 6 months after the last infusion. Breastfeeding is contraindicated during treatment and for 6 months following the final rituximab dose.