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Skin-nontumor / Clinical Dermatology

Other dermatoses

Dermatomyositis


Reviewer: Mowafak Hamodat, MB.CH.B, MSc., FRCPC, Eastern Health, St. Johns, Canada (see Reviewers page)
Revised: 23 July 2011, last major update Julye 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Clinical features
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● Autoimmune inflammatory disease of skeletal muscle and skin, usually affects women
● Symmetric proximal muscle weakness and skin lesions
● Affects face, dorsal hands and feet, particularly knuckles
● 20% of cases lack muscle involvement (Arch Dermatol 2010;146:26)
● 15% have coexisting adenocarcinoma of stomach, breast, ovary, lung or colon, with remission of dermatomyositis following tumor resection; high risk of nasopharyngeal carcinoma in Asian patients (Ann Acad Med Singapore 2010;39:843)
● Increased risk of thyroid disease, particularly hypothyroidism, especially in patients with interstitial lung disease
Polymyositis: similar muscle changes without skin changes

Treatment
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● Steroids, immunosuppressants (Arthritis Care Res (Hoboken) 2010;62:219), tumor resection (if present)

Clinical description
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● Poorly demarcated, scaly, erythematous patches
● Also heliotrope erythema of upper eyelids and extensor joint surfaces

Clinical images
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Purple plaques on knees


Heliotrope rash and Gottron's papules


Various images

Micro descriptions
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● Chronic nonspecific dermatitis or interface dermatitis resembling systemic lupus erythematosus
● Often atrophic epidermis with prominent vacuolar interface change
● Sparse perivascular lymphocytic infiltrate with markedly increased dermal mucin
● Muscles show myositis with myofiber necrosis, fragmentation and phagocytosis; late myofiber atrophy, fibrosis and fatty change

Micro images
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Erythrodermic dermatomyositis

   
Interface dermatitis with vacuolar alteration at dermal-epidermal junction

Positive stains
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● C5-9 (by immunofluorescence)

Negative stains
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● IgG, IgA, and IgM by immunofluorescence

Additional references
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eMedicine

End of Skin-nontumor / Clinical Dermatology > Other dermatoses > Dermatomyositis


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