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.
Richard J. Moskowitz, MD, Dermatologist in Private Practice, Mineola, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.