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Dermatomyositis N021

Last amended 
14 July 2022
Current RMA Instruments
Reasonable Hypothesis SOP
70 of 2022
Balance of Probabilities SOP
71 of 2022
Changes from previous Instruments

SOP Bulletin 231

ICD Coding
  • ICD-10-AM Code: M33.1
Brief description

This is a chronic systemic autoimmune disease.  The main manifestations are inflammation of the skin (with rashes) and muscle weakness.

Confirming the diagnosis

This is a complicated diagnosis.  Characteristic skin findings together with other manifestations and a laboratory finding may be sufficient for diagnosis, but in some cases muscle or skin biopsy will be required.  Features may overlap with other rheumatic diseases such as systemic lupus erythematosus and systemic sclerosis.

The relevant specialist is a rheumatologist/physician, or for amyopathic dermatomyositis, a dermatologist. 

Additional diagnoses covered by SOP
  • Amyopathic dermatomyositis
  • Dermatomyositis sine myositis
Conditions excluded from SOP
  • Eosinophilic myositis
  • Inclusion body myositis
  • Polymyositis
Clinical onset

The condition may have a sudden or gradual onset.  Skin rashes/changes are the most common initial feature.  Progressive proximal muscle weakness is usually present.  Other manifestations include lung inflammation, polyarthritis and dysphagia. 

Clinical worsening

The condition is generally responsive to treatment but may relapse or be resistant to treatment in some cases.  Glucocorticoids (steroids) are a mainstay of treatment and may be required for prolonged periods. Development of complications of steroid treatment is not worsening of dermatomyositis, but rather onset of a new problem.  Worsening may be evidenced by worsening of skin changes, muscle weakness or other early manifestations, or by the development of new features attributable to the disease.