This is Gottron's 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: 2/11/2013 Reviewed By: Reviewed by: Ariel D. Teitel, MD, MBA, Clinical Associate Professor of Medicine, NYU Langone Medical Center. Review provided by VeriMed Healthcare Network. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.