OverviewThe appearance of purple (violaceous) plaques on the knees may be associated with dermatomyositis. Typically, most lesions associated with other diseases are red (erythematous).
Update Date 1/20/2015
Updated by: Gordon A. Starkebaum, MD, professor of medicine, division of rheumatology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.