Dermatomyositis in adults is discussed in detail in Chapter 34: Cutaneous Manifestations of Systemic Disease. The juvenile form for dermatomyositis and its characteristic distinguishing features will be discussed in this section.
Juvenile dermatomyositis (JDM), the most common inflammatory myopathy in children, occurs in 3 per million children, and more often in girls.
Incidence of JDM peaks between 2 and 5 years of age and at 12 to 13 years of age.
Onset is usually gradual with subtle symptoms including low-grade fever, malaise, weight loss, poor appetite, pruritus, and photosensitivity of affected skin areas. Occasionally, the onset is rapid with fevers and severe muscle weakness.
The cutaneous features are seen at presentation in the vast majority of patients with JDM and range from very subtle to striking.
Violaceous telangiectatic erythema with or without scaling on the sun-exposed areas of the body is characteristic (Fig. 10.7). When present around the eyes and eyelids it is called the heliotrope rash (see Fig. 34.25). When present on the dorsal knuckles it is called Gottron sign and on shoulders and chest it is referred to as the Shawl sign (see Figs. 34.27 and 34.28).
Gottron papules are a pathognomonic sign of JDM and appear as grouped erythematous or violaceous, flat-topped papules on the dorsal metacarpal phalangeal and proximal phalangeal joints (Fig. 10.8 [see Fig. 34.26]).
Periungual telangiectasias and erythema with thickened, unkempt appearing cuticles are also characteristic of JDM (Fig. 10.9 [see Figs. 34.17 and 34.30]).
Calcinosis cutis occurs in up to 40% of patients with JDM and presents as firm, yellow- or flesh-colored nodules, often over bony prominences.
Other skin features that occur less often include palmar erythema and thickening, panniculitis presenting as tender, indurated plaques and nodules on the arms, thighs, and buttocks, and nonscarring alopecia.
With long-standing disease some affected children develop very itchy dry skin with poikiloderma (telangiectasia, atrophy, hyperpigmentation, and hypopigmentation), and lipodystrophy may occur especially if condition is not well controlled.
Pitted ulcerations of distal aspects of the limbs are a sign of severe disease.
Muscle weakness affects the large proximal muscles and is bilateral and progressive.
Patients may report an inability to comb hair or difficulty climbing stairs and young children may show more demanding behavior or complaints of fatigue and not wanting to walk or reach for things.
Arthritis usually is asymptomatic and of the large joints occurs in half of the affected children.
Diagnosis is usually made on clinical grounds by identifying the characteristic clinical features and the muscle weakness.
One or more muscle enzymes including serum aldolase, aspartate aminotransferase, lactic dehydrogenase, and serum creatine phosphokinase will be elevated.
Management 
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