Myositis

Myositis is the inflammation of muscle and is considered a generic non-specific term. Myopathy refers to a broad range of diseases of skeletal muscle that lead to dysfunction of muscle fibres, some. Myositis is the subset of which are cause myositismyopathy characterized by inflammation of muscle. There There is often significant overlap leading to the terms being used interchangeably.

Pathology

MyositisEtiology

There are numerous specific types of myositis, whichMyopathies and myositides can be generally categorised as follows¹:

• 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 myositis³
  • bacterial myositis: may be complicated by (pyomyositis)
  • viral myositis: may be complicated by
    • 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 or myopathy
  • statin-related myositis: can persist after discontinuation of the drug
  • steroid myopathy

Myositis ossificans is considered a different entity.

Myopathy

Myopathies can be generally categorised as follows:

• hereditary myopathiesmyopathy
  • enzymatic deficiencies
  • inborn errors of metabolism (e.g. glycogen storage disease)
• inflammatory and infectious myositides: see above
• endocrine myopathiesmyopathy
  • associated with adrenal, thyroid, parathyroid and pituitary dysfunction
• drug-induceddenervation myopathy
  • such as corticosteroids
• systemic conditions, such as sarcoidosisdue to peripheral neuropathy

Radiographic features

MRMRI 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.