The appearance of purple (violaceous) plaques on the knees may be associated with dermatomyositis. Typically, most lesions associated with other diseases are red (erythematous).
Review Date 1/10/2019
Updated by: Gordon A. Starkebaum, MD, MACR, ABIM Board Certified in Rheumatology, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.