Ans. A. ANCA
Investigating for ANCA should be the next step to narrow down to the associated vasculitis.
Antineutrophil cytoplasmic antibodies (ANCA)
Many patients with vasculitis have circulating antibodies that react with neutrophil cytoplasmic antigens: Antineutrophil cytoplasmic antibodies (ANCAs), which are heterogeneous groups of autoantibodies directed against constituents of neutrophil primary granules, monocyte lysosomes, and endothelial cells.
Two are most important: Anti-proteinase-3 (PR3-ANCA, previously c-ANCA) and anti-myeloperoxidase (MPO-ANCA, previously p-ANCA).
PR3 is a neutrophil azurophilic granule constituent. PR3 ANCA can be triggered by certain infections.
MPO is a lysosomal granule constituent involved in oxygen-free radical generation. MPO-ANCAs are induced by several therapeutic agents particularly propylthiouracil.
Since ANCA autoantibodies are directed against cellular constituents and do not form circulating immune complexes, the vascular lesions do not typically contain demonstrable antibodies and complement – described as “pauci-immune.”PR3.
ANCA Associated Vasculitis (AAV) comprises a group of multi-systemic diseases affecting small-to-medium-sized vessels. It is categorized into 3 distinct forms: (Kidney biopsies typically demonstrate crescentic glomerulonephritis with little or no immune complex deposition):
- Granulomatosis with polyangiitis (GPA; formerly Wegener granulomatosis)
- Microscopic polyangiitis (MPA)
- Eosinophilic granulomatosis with polyangiitis, formerly called Churg- Strauss syndrome (CSS)