Induction failure in granulomatosis with polyangiitis: a nationwide case-control study of risk factors and outcomes.

To identify characteristics of granulomatosis with polyangiitis (GPA) associated with induction failure, describe salvage therapies and their efficacy. We conducted a nationwide retrospective case-control study of GPA with induction failure between 2006 and 2021. Each patient with induction failure was randomly paired to three controls matched for age, sex and induction treatment. We included 51 patients with GPA and induction failure (29 men and 22 women). At induction therapy, median age was 49 years. Twenty-seven patients received intravenous cyclophosphamide (ivCYC) and 24 rituximab (RTX) as induction therapy. Patients with ivCYC induction failure more frequently had PR3-ANCA (93% vs 70%, P = 0.02), relapsing disease (41% vs 7%, P < 0.001) and orbital mass (15% vs 0%, P < 0.01) compared with controls. Patients with disease progression despite RTX induction therapy more frequently had renal involvement (67% vs 25%, P = 0.02) with renal failure (serum creatinine >100 µmol/l in 42% vs 8%, P = 0.02) compared with controls. After salvage therapy, remission was achieved at 6 months in 35 (69%) patients. The most frequent salvage therapy was switching from ivCYC to RTX (or vice versa), showing an efficacy in 21/29 (72%). Remission was achieved in nine (50%) patients with inappropriate response to ivCYC, while in patients with progression after RTX induction, remission was achieved in four (100%) who received ivCYC (with or without immunomodulatory therapy), but only in three (50%) after adding immunomodulatory therapy alone. In patients with induction failure, characteristics of GPA, salvage therapies and their efficacy vary according to induction therapy and failure modality.

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