Last revised by Yuranga Weerakkody on 14 Nov 2021

Dermatomyositis is an autoimmune inflammatory myositis, which like its closely-related condition polymyositis, carries an increased risk of malignancy.

There is a recognized female predilection. It has a bimodal age of presentation depending on the variant:

The classic presentation is that of a symmetrical proximal myopathy with associated dermatological changes which includes a dusky-red rash over the face, arms, hands, legs and other features (e.g. Gottron papules). Dysphagia, myalgia, fever and weight loss are other features 7.

There is a sixfold increased risk of malignancy in dermatomyositis (cf. twofold in polymyositis) 8. Multiple risk factors for the development of malignancy have been identified 8:

Several factors increase the risk of malignancy 8:

There is cell-mediated injury targeted at striated muscle with resultant atrophy, edema, coagulation necrosis, fibrosis and calcification.

  • elevated muscle enzymes (e.g. CK)
  • elevated muscle specific antibodies
    • anti-RNA
    • anti-Mi2
  • typically shows dystrophic calcification in muscles and soft tissues (calcinosis universalis)
    • sheet-like although at least four patterns have been described with childhood dermatomyositis 4
    • classically seen affecting the thigh regions
  • chest radiograph may show diaphragmatic elevation
  • acro-osteolysis
  • may show disordered peristalsis involving the upper esophagus i.e. the portion supplied by skeletal muscle
  • T2: generally hyperintense signal throughout the affected muscles; calcific areas may be low signal; peri-muscular edema may additionally appear as high signal; signal intensity may return to normal after treatment 4

General imaging differential considerations include:

MRI T2-weighted sequences are useful to guide muscle biopsy: 

  • areas of edema related to the active inflammatory process
  • non-specific end-stage fatty atrophic muscle should be avoided 

Further imaging in the form of a contrast-enhanced CT of the chest, abdomen and pelvis may be undertaken to exclude an associated primary malignancy.

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Cases and figures

  • Case 1
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  • Case 2
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  • Case 3
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  • Case 4
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  • Case 5: with hip AVN from steroid therapy
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  • Case 6
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  • Case 7: affecting whole body
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  • Case 8: with pulmonary involvement
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  • Case 9: juvenile
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  • Case 10
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  • Case 11: with calcinosis universalis
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  • Case 12: dermatomyositis
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  • Case 13
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