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About Dermatomyositis

A type of auto immune inflammatory myositis (recognized in females).It has 2 types according to age of presentation :
1- Juvenile dermatomyositis (JDM) : affects children and tends to be more severe
2- Adult dermatomyositis (ADM) : typically affects adults around the age of 50

It`s pathology described as cell mediated injury targeted at striated muscle with resultant atrophy, oedema, coagulation necrosis, fibrosis and calcification.
-There is elevation of:  * muscle enzymes (CK)
* elevated muscle specific antibodies
o anti RNA
o anti Mi2

Dermatomyositis may be associated with
interstitial lung disease : typically gives a patchy and subpleural consolidation with parenchymal bands.
internal malignancy  : can occur as part of a paraneoplastic syndrome (e.g lung cancer)

Radiographic features
Plain film
Plain radiographs show extensive sheet-like dystrophic calcifications in the soft tissues of the leg consistent with dermatomyositis.
* typically shows dystrophic calcification in muscles and soft tissues (calcinosis universalis)
o sheet like although at least four patterns have described with childhood dermatomyositis 4.
o classically seen affecting the thigh regions
* chest radiograph may show diaphragmatic elevation
* acroosteolysis

Barium swallow
* may show disordered peristalsis involving the upper oesophagus : portion supplied by skeletal muscle

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 .

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