MPO and rheumatoid arthritis: This coexistence may not be entirely coincidental, as evidenced by facts such as ANCA positivity in 20% of RA patients [25], a positive association between ANCA titer and rapid joint destruction in early RA [26], the presence of myeloperoxidase-ANCA in synovial fluid of RA patients [27], and AAV sharing susceptibility loci with RA [28, 29].