This accelerated trajectory was clinically notable and raised concern for a systemic process beyond infection. An autoimmune screen revealed a high proteinase 3 (PR3)-ANCA and rheumatoid factor, while other autoantibodies, including C-ANCA, MPO-ANCA, antinuclear antibody (ANA), extractable nuclear antigen (ENA), anti-GBM, anti-cyclic citrullinated peptide (CCP), cardiolipin, and myositis profile were negative. Here, PRTN3 is linked to myositis disease.