Images of Memorable Cases: Case 32 32. Dermatomyositis The erythematous, sometimes scaly, rash of dermatomyositis characteristically occurs on the knuckles of the hands and over the patellae, olecranon processes, and medial malleoli. In fact, violaceous plaques (Gottron’s papules) appearing over the metacarpophalangeal and interphalangeal joints—but sparing the dorsal phalangeal surfaces—are virtually pathognomonic of dermatomyositis.