Double Booked: Dual ANCA-Associated Vasculitis

Introduction: Dual anti-neutrophil cytoplasmic antibody (ANCA) positivity, characterized by the presence of both proteinase 3 (PR3) and myeloperoxidase (MPO) antibodies, is an uncommon presentation of ANCA-associated vasculitis (AAV). AAV is an autoimmune disorder that often affects small vessels, leading to organ damage, mainly in the kidneys and lungs. This case report describes a 69-year-old male with dual ANCA positivity who presented with progressive glomerulonephritis. Case Description: A 69-year-old male with a history of hypertension and chronic kidney disease (CKD) stage III was undergoing an evaluation for proteinuria and hematuria when he was found to have dual ANCA positivity. Laboratory tests revealed an anti-PR3 antibody level of 5.4 U, an MPO antibody level of 461 U, and no evidence of hepatitis B or C. A kidney biopsy showed two distinct pathologies: cellular crescents indicating AAV and diffuse capillary staining and subendothelial deposits indicating membranous nephropathy (MN). Upon presentation to the ED for worsening hematuria, patient was started on oral prednisone 60 mg daily. However, due to worsening renal function, he was transitioned to IV methylprednisolone at 1 g daily for three days and subsequently IV Rituximab 1 g with a repeat dose in two weeks. Patient had improvement in creatinine and proteinuria following treatment. Discussion: Dual ANCA positivity is a rare severe variant of AAV, often associated with aggressive renal disease. Given the high MPO titer and rapid progression of kidney dysfunction, an aggressive immunosuppressive regimen was chosen. Furthermore, this patient had MN seen on biopsy. Dual positive ANCA vasculitis and MN are uncommonly seen together in a clinical picture. This case highlights the importance of recognizing dual ANCA positivity as potentially severe requiring prompt diagnosis and intensive treatment. It also highlights the importance of reviewing urine studies to assess for hematuria and/or proteinuria as these quite often may be the first clue for an underlying glomerular disorder.