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Dermatomyositis

Dermatomyositis is an auto immune inflammatory myositis.

Epidemiology

There is a recognised female predilection. 

It has a bimodal age of presentation depending on the variant:

Pathology

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

Markers
  • elevlated muscle enzymes (CK)
  • elevated muscle specific antibodies 
    • anti RNA
    • anti Mi2
Associations
  • interstitial lung disease 2 - typically gives a patchy and subpleural consolidation with parenchymal bands. 
  • internal malignancy 1 - can occur as part of a paraneoplastic syndrome (e.g lung cancer)

Radiographic features

Plain film 
  • typically shows dystrophic calcification in muscles and soft tissues (calcinosis universalis)
    • sheet like although at least four patterns have described with childhood dermatomyositis 4.
    • classically seen affecting the thigh regions
  • chest radiograph may show diaphragmatic elevation
  • acroosteolysis
Fluoroscopy
Barium swallow
  • may show disordered peristalsis involving the upper oesophagus : portion supplied by skeletal muscle
MRI 

T2 - generally hyper intense signal throughout the affected muscles ; calcific areas may be low signal ; perimuscular oedema may additionally appear as high signal ; signal intensity may return to normal after treatment 4.

Differential diagnosis

General imaging differential considerations include

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