Doppelgängers are double walkers with similar features. GPA and IgG-RD are doppelgängers. 3 findings in GPA that are not found in IgG4-RD: ◦ Granulomatous inflammation ◦ Necrosis ◦ Neutrophilic infiltration John Stone, Secrets and Pearls #ACR22 @RheumNow https://t.co/F67EhGBcS4