• Systemic connective tissue disease characterized by inflammatory and degenerative changes in proximal muscles, sometimes accompanied by characteristic skin rash
    • If skin manifestations (Gottron sign [symmetric, scaly, violaceous, erythematous eruption over the extensor surfaces of the metacarpophalangeal and interphalangeal joints of the fingers]; heliotrope [reddish violaceous eruption on the upper eyelids]) are present, it is designated as dermatomyositis.
    • Different types of myositis include the following (1):
      • Idiopathic polymyositis
      • Idiopathic dermatomyositis
      • Polymyositis/dermatomyositis as an overlap (usually with lupus or systemic sclerosis or as part of mixed connective tissue disease)
      • Myositis associated with malignancy
      • Necrotizing autoimmune myositis (often statin associated)
      • Inclusion body myositis (IBM), a variant with atypical patterns of weakness and biopsy findings
  • System(s) affected: cardiovascular, musculoskeletal, pulmonary, skin/exocrine
  • Synonym(s): myositis; inflammatory myopathy; antisynthetase syndrome (subset with certain antibodies)



  • Estimated at 1.2 to 19 per million population per year
  • Predominant age: 5 to 15 years, 40 to 60 years, peak incidence in mid-40s
  • Predominant sex: female > male (2:1)

2.4 to 33.8 patients per 100,000 population

Geriatric Considerations
Elderly patients with myositis or dermatomyositis are at increased risk of neoplasm.

Pediatric Considerations
Childhood dermatomyositis is likely a separate entity associated with cutaneous vasculitis and muscle calcifications.

Etiology and Pathophysiology

  • Inflammatory process, mediated by T cells and cytokine release, leading to damage to muscle cells (predominantly skeletal muscles)
  • In patients with IBM, degenerative mechanisms may be important.
  • Unknown; potential viral, genetic factors

Mild association with human leukocyte antigen (HLA)-DR3, HLA-DRw52

Risk Factors

Family history of autoimmune disease (e.g., systemic lupus erythematosus (SLE), myositis) or vasculitis

Commonly Associated Conditions

  • Malignancy more common in dermatomyositis subtype, older patients
  • Progressive systemic sclerosis
  • Vasculitis
  • SLE
  • Mixed connective tissue disease

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