The classic skin manifestation of dermatomyositis is the heliotrope rash, characterized by a violaceous or dusky discoloration on the eyelids often accompanied by periorbital edema. This rash is highly specific and helps distinguish dermatomyositis from other connective tissue diseases. It reflects the underlying microvascular injury and inflammation typical of dermatomyositis. In contrast, the butterfly rash is typical of systemic lupus erythematosus, while erythema nodosum and livedo reticularis occur in other conditions. Recognizing the heliotrope rash aids in early diagnosis and management of dermatomyositis.

Reference: Harrison's Principles of Internal Medicine, Jameson et al., 20th Edition.