This is Gottron sign, seen in dermatomyositis (an inflammatory disease of the muscles and skin). Violet-colored inflammation over the knuckles is an important diagnostic finding in dermatomyositis, since other skin conditions produce more redness.
Review Date 1/31/2021
Updated by: Diane M. Horowitz, MD, Rheumatology and Internal Medicine, Northwell Health, Great Neck, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.