Myeloperoxidase-antineutrophil cytoplasmic antibody-positive granulomatosis with polyangiitis: a rare serological variant

Granulomatosis with polyangiitis (GPA) is a necrotizing small-to medium-vessel vasculitis classically associated with PR3-antineutrophil cytoplasmic antibody (ANCA)-positive status.However, some patients present a myeloperoxidase (MPO)-ANCA-positive status, leading to diagnostic overlap with microscopic polyangiitis and potential delays in appropriate treatment.This distinction has important prognostic implications, as PR3-ANCA-positive patients have a higher risk of relapse, whereas MPO-ANCA-positive patients may develop greater cumulative organ, particularly renal, damage.We report a 48-year-old woman presenting with inflammatory arthritis, recurrent sinusitis, acute kidney injury, and pulmonary involvement.Laboratory tests showed MPO-ANCA-positive and PR3-ANCA-negative results.Renal biopsy revealed pauci-immune necrotizing proliferative glomerulonephritis with granulomatous features.Treatment with high-dose glucocorticoids and rituximab led to clinical stabilization.This case highlights the importance of clinicopathologic correlation for timely diagnosis, with a direct impact on prognosis and therapeutic strategy.