Clinical Pearl at #ACR21 from Dr. J. Stone: ⭐️Tissue biopsy is not essential in diagnosing IgG4-related dz in a pt w/ a typical pattern of retroperitoneal fibrosis. ⭐️Periaortitis ("coated" aorta) w/ "hairy" kidney is NOT IgG4 but rather Erdheim-Chester Dz #ACRBest @Rheumnow https://t.co/2tB9p3c7W7