Myositis

Myositis (plural: myositides) is the subset of myopathy characterized by inflammation of skeletal muscle.

Pathology

Etiology

Myositides can be generally categorized by etiology as follows ¹:

• inflammatory myositis
  • dermatomyositis
  • polymyositis
  • antisynthetase syndrome
  • immune-mediated necrotizing myopathy
  • inclusion body myositis
  • proliferative myositis
  • eosinophilic myositis
  • granulomatous myositis
    • sarcoid myositis
    • chronic graft versus host disease ²
• infectious myositis ³
  • bacterial myositis (pyomyositis)
  • viral myositis
    • influenza myositis
    • coxsackievirus B virus-related pleurodynia (Bornholm disease)
    • virus-associated rhabdomyolysis
  • parasitic myositis (a cause of eosinophilic myositis)
    • cysticercosis
    • trichinosis
  • fungal myositis (rare)
• drug-related myositis
  • statin-related myositis
• trauma or iatrogenic myositis
  • ​myositis ossificans
  • radiation-induced myositis ⁴

Radiographic features

MRI is the gold standard modality for non-invasive evaluation of myositis, which shows a classic edema signal pattern (high T2WI and STIR signal) in affected muscles. Inflamed muscles demonstrate contrast enhancement.

If chronic, T1WI will show high muscle signal indicating fat replacement and atrophy.