Rare Case of Renal Limited Dual Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis: Double Trouble!

Dual anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) characterized by the presence of both anti-proteinase-3 (PR3-ANCA) and anti-myeloperoxidase (MPO-ANCA) antibodies is a rare clinical entity. Only few cases have been reported previously, most of which were associated with infections, drugs, autoimmune diseases and malignancies. Herein, we describe a young woman who presented with rapidly progressive glomerulonephritis with hypocomplementemia and markedly elevated anti-PR3 and anti-MPO titres. Meticulous work-up ruled out all possible secondary causes. Renal biopsy showed the presence of focal fibrocellular crescents with focal mesangial hypercellularity. Immunofluorescence and electron microscopy showed pauci-immune deposits. The patient was treated with an induction regimen comprising oral prednisolone and cyclophosphamide. She attained both clinical and serological remission at 3 months and is currently on an azathioprine-based maintenance regimen. We have extensively reviewed all previous cases of dual AAV and have formulated an approach to diagnose and treat this rare entity. LEARNING POINTS: Dual anti-neutrophil cytoplasmic antibody-associated vasculitis characterized by both PR3-ANCA and MPO-ANCA antibodies is a rare clinical entity. Prior to treating with immunosuppression, we need to rule out secondary aetiologies such as drugs, certain infections, autoimmune diseases and haematological malignancies. Atypical presentations such as hypocomplementemia, other serological abnormalities like positive ANA, cryoglobulins, anti-histone antibody and histology showing mesangial hypercellularity, interstitial inflammation and lack of pauci-immunity, may create a diagnostic dilemma.