Dermatomyositis (DM) is a systemic autoimmune disorder with skin, muscle involvement, and other manifestations including polyarthritis, interstitial lung fibrosis, and, in 20–25 % of the cases, a coexistent malignancy. Muscle symptoms include proximal limb weakness, myalgia, and tenderness. In classic dermato-/polymyositis, cutaneous manifestation occurs in 30–40 % of the adult and 95 % of the juvenile cases. 4–8.2 % of the patients with DM show exclusively skin symptoms and never develop muscle involvement. Photosensitivity is an important clinical feature of DM. Skin symptoms include a violaceous erythema, Gottron’s papules appearing over the metacarpophalangeal, interphalangeal, elbow, and knee joints. DM-related skin symptoms also include periorbital (heliotrope) edematous rash overlying of the eyelids and periorbital tissue. A diffuse flat purple-red skin violaceous erythema may also be present on the dorsal surface of the arms and fingers; over the deltoids, posterior shoulders, and neck (“shawl sign”); V area of anterior neck and upper chest; and central aspect of the face. Periungual telangiectasia also belongs to the typical DM-related skin signs. Further secondary changes of DM include scale, follicular hyperkeratosis, pigmentary changes, subepidermal bullous change, and ulceration. Poikiloderma atrophicans vasculare (poikilodermatomyositis) that is a circumscribed violaceous erythema with associated telangiectasia, hypopigmentation, hyperpigmentation, and superficial atrophy may be present in certain parts of the body including the V area of anterior neck and upper chest, back, flanks, and buttocks. Occasionally, calcinosis cutis may also appear. The term amyopathic DM (ADM) (synonymous with “DM sine myositis”) and furthermore a closely related form of DM, “hypomyopathic DM,” (HDM) are characterized by the appearance of typical skin disease for at least 6 months without having any muscle weakness. Cancer-associated DM is probably much more prevalent in adults than it has previously been suspected. Almost all children with DM also develop cutaneous manifestations usually before the diagnosis of myositis.
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