Myositis

Myositis 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 noninvasive evaluation of myositis, which shows 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.