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Dermatomyositis is a multisystem autoimmune connective tissue disease that is most often characterized by a symmetric proximal extensor inflammatory myopathy, a characteristic violaceous cutaneous eruption, and pathogenic circulating autoantibodies. Dermatomyositis demonstrates a bimodal incidence, with the adult form most commonly seen in individuals aged 45-60, and the juvenile form found in children aged 10-15 years. A 2:1 female-to-male incidence ratio exists in adults.

While the etiology remains unclear, some evidence suggests that genetically susceptible individuals with certain HLA types mount aberrant cellular and humoral responses after exposure to malignancy, infection, or drug ingestion.

Clinical features of dermatomyositis can be categorized into cutaneous and systemic manifestations. Typical findings include a heliotrope rash, atrophic dermal papules of dermatomyositis (ADPDM; previously Gottron's papules), shawl sign, holster sign, photosensitivity, flagellate erythema, poikiloderma, calcinosis cutis and nail fold changes. Pruritus is also common.

Systemic manifestations of dermatomyositis include fatigue, malaise, myalgias, and the following:

• Musculoskeletal 鈥� Proximal extensor muscle group inflammation that leads to muscle pain and weakness. Patients may have difficulty getting up from a sitting position or combing their hair.
• Gastrointestinal 鈥� Dysphagia can be seen due to esophageal muscle involvement.
• Pulmonary 鈥� Some level of pulmonary involvement will be present in 15%-30% of patients. Diffuse interstitial fibrosis and acute respiratory distress syndrome are manifestations of pulmonary involvement.
• Cardiac 鈥� Tachycardia or bradycardia, bundle branch blocks, cardiomegaly or congestive heart failure.

In addition, the clinician should be aware of several key points in patients with dermatomyositis:

• Malignancy 鈥� Up to 40% of patients with the adult form may have an occult malignancy. Initial cancer screening and vigilant serial monitoring for 2-3 years post diagnosis is strongly recommended. Chest, abdomen, and pelvis CT scanning 鈥� even in the absence of symptoms 鈥� should be considered. Commonly found malignancies include colon, ovarian, breast, pancreatic, lung, and gastric cancers and lymphoma. The juvenile form does not share this risk.
• Autoimmune disease overlap 鈥� Dermatomyositis can occur in conjunction with systemic lupus erythematosus (SLE), mixed-connective tissue disease, Sj枚gren syndrome, scleroderma, and rheumatoid arthritis. Scleroderma / CREST syndrome (calcinosis cutis, Raynaud phenomena, esophageal dysfunction, sclerodactyly, and telangiectasia) is the most common overlap syndrome resulting in sclerodermatomyositis.
• Antisynthetase syndrome 鈥� Fever, Raynaud phenomenon, "mechanic's hands," interstitial pulmonary fibrosis, polyarthritis, and autoantibodies to aminoacyl-tRNA synthetase.
• Variants 鈥� Dermatomyositis sine myositis is the amyopathic form where dermatomyositis is clinically limited to cutaneous involvement. Disease is often detectable on muscle MRI, and many of these patients go on to develop muscle weakness as the disease progresses. This is associated with the anti-CADM-140/MDA5 antibody.
• Dermatomyositis and Degos disease are, rarely, associated.
• Dermatomyositis may be induced by medications, including hydroxyurea, penicillamine, interferon beta, and ipilimumab.

With proper therapy, 75% of patients can be disease free within 3 years.

What To Look For:

• A heliotrope rash, a violaceous edematous periorbital erythema that may be slightly scaly, is considered pathognomonic for dermatomyositis.
• ADPDM (previously Gottron's papules) appear as red to purple, scaly, flat-topped papules on the dorsal metacarpophalangeal joints. They may be telangiectatic and may eventually atrophy. Macular erythema may be seen in this anatomic distribution as well.
• Linear violaceous macules may be seen. These extend from elbows down forearms, knees to the thighs, or ulnar styloid up the forearms.
• "Mechanic's hands" refers to the hyperkeratosis, scaling, fissuring, and hyperpigmentation on the ulnar aspect of the thumb and radial side of the fingers.
• Nailfold changes are commonly observed including erythema and telangiectasias at the base of the nails with prominent capillary loops. Thickening, roughness, hyperkeratosis, and irregularity of the cuticle with little or no redness are frequent.
• Photoexacerbated macular or poikilodermatous erythema of the upper back and posterior neck and shoulders (shawl sign) or anterior neck and upper chest (V sign).
• Violaceous poikilodermatous scaly plaques can be found over the lateral hip (holster sign).
• Flagellate erythema: fixed linear pink macules develop in pruritic skin.
• Muscle strength should be assessed. In addition, MRI of the proximal muscle groups can demonstrate increased T2-weighted signal density and correlates with inflammation.
• Other cutaneous manifestations include vesicles, bullae, lichenoid papules, and calcinosis cutis (especially in juvenile versions).
• Scalp involvement may be present in the majority of patients but is frequently misdiagnosed as psoriasis or seborrheic dermatitis. It is characteristically very pruritic. Scalp lesions generally appear as diffuse, atrophic, erythematous, scaly plaques, often with some degree of alopecia.

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