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