Skin nontumor

Lichenoid and interface reaction patterns


Topic Completed: 1 July 2011

Minor changes: 10 November 2020

Copyright: 2002-2021,, Inc.

PubMed Search: Dermatomyositis [title] skin "loattrfree full text"[sb]

Mowafak Hamodat, M.B.Ch.B., M.Sc.
Page views in 2020: 6,412
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Cite this page: Hamodat M. Dermatomyositis. website. Accessed October 25th, 2021.
Definition / general
  • See also Muscle chapter
  • 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
Clinical features
  • Poorly demarcated, scaly, erythematous patches
  • Also heliotrope erythema of upper eyelids and extensor joint surfaces
Clinical images

Images hosted on other servers:

Purple plaques on knees

Heliotrope rash and Gottron papules

Various images

Microscopic (histologic) description
  • 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
Microscopic (histologic) images

Contributed by Hillary Rose Elwood, M.D.

Subtle vacuolar interface change and increased dermal mucin highlighted by Alcian blue stain

Images hosted on other servers:

Erythrodermic dermatomyositis

Interface dermatitis
with vacuolar
alteration at dermal
epidermal junction

Positive stains
  • C5-9 (by immunofluorescence)
Negative stains
  • IgG, IgA and IgM by immunofluorescence
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