Key Points

• Dermatomyositis, presumably an autoimmune disease, is triggered by malignancy, drugs, or infection.

• High-dose corticosteroids with a slow taper over 2 to 4 years are the primary treatment, and muscle disease usually responds more rapidly than skin disease.

Dermatomyositis is presumably an autoimmune disease that is triggered by an outside factor. Antinuclear antibodies or anticytoplasmic antibodies (antisynthetase) are found in up to 95% of patients. Clinically, dermatomyositis is characterized by a symmetric proximal inflammatory myopathy and distinct skin lesions. Proximal muscle weakness may precede the skin findings, may follow them, or may be absent ("dermatomyositis sine myositis"). Classic cutaneous lesions include the heliotrope rash, pink to lilac, poikilodermatous or edematous patches of the periocular skin (Fig. 33-72). The shawl sign consists of poikiloderma of the upper chest, shoulders, and upper back. Gottron's papules are erythematous, scaly or lichenified papules or plaques over the knuckles. Similar plaques may be seen on the elbows, mimicking psoriasis. Other common cutaneous findings are periungual telangiectasias (visible dilated capillary loops) and ragged cuticles (cuticular dystrophy).

Although the etiology of dermatomyositis is unknown, triggers may include malignancy, drugs, and infection. In

Figure 33-72 Heliotrope rash of dermatomyositis. ©J Richard P. Usatine.) Figure 33-73 Cutaneous sarcoidosis. © Richard P. Usatine.)

adults with dermatomyositis, studies report a wide range of association with internal malignancy (10%-50%). Common malignancies include genitourinary, ovarian, colon, breast, lung, pancreatic, and lymphoma. The same association is not found in juvenile cases of dermatomyositis. Therefore, any adult with a new diagnosis of dermatomyositis should be screened with a chest-abdominal-pelvic CT scan with close surveillance for 2 to 3 years.

Double-blind, placebo-controlled trials are lacking for this rare disease, but the mainstay of treatment for dermatomyo-sitis is high-dose corticosteroids with slow taper over 2 to 4 years. Other immunosuppressants used include methotrexate, azathioprine, cyclophosphamide, and cyclosporine. In general, the myopathy responds more rapidly and easily than the skin lesions, and severe pruritus can persist long after muscle disease is controlled. For skin lesions, sun protections, topical corticosteroids, or antimalarials may help.

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