Dual Anti‐Neutrophil Cytoplasmic Antibody and Anti‐Glomerular Basement Membrane Antibody‐Positive Crescentic Glomerulonephritis in a Patient With Monoclonal Gammopathy and Elevated <scp>IgG4</scp> Levels: A Case Report and Literature Review

The aetiology of crescentic glomerulonephritis is multifactorial, with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) and anti-glomerular basement membrane (GBM) antibody disease being well-documented causes. Monoclonal immunoglobulin and immunoglobulin G4 (IgG4)-related diseases can also exacerbate kidney damage through varying mechanisms. However, cases where both ANCA and anti-GBM antibodies are positive, in the presence of serum M protein and elevated IgG4 levels, have not yet been reported. We herein report the first patient with dual ANCA and anti-GBM antibody-positive crescentic glomerulonephritis, along with monoclonal gammopathy and elevated IgG4 levels.