polymyositis and dermatomyositis

Last edited 10/2022 and last reviewed 10/2022

Polymyositis and dermatomyositis are systemic connective tissue diseases which are characterised by acute and chronic inflammation of striated muscle. In dermatomyositis there is an accompanying dermatitis. The limb girdle or proximal muscles are most severely affected but their bulk is preserved beyond that expected from their weakness: this is an important sign distinguishing this condition from a limb girdle dystrophy.

Myositis is usually the initial presentation. Some patients present with dermatitis and later develop muscle weakness; rarely, only dermatitis occurs.

The aetiology is unknown but there is an association with HLA-B8 and HLA-DR3.

Dermatomyositis in males over the age of 60 years may be suggestive of an underlying systemic malignancy.

Treatment options include:

  • glucocorticoids with or without second-line immunosuppressive agents including methotrexate, azathioprine, mycophenolate mofetil, and, in refractory cases, IVIG (intravenous immunoglobulin) or rituximab
  • in a 16-week trial involving adults with dermatomyositis, the percentage of patients with a response of at least minimal improvement based on a composite score of disease activity was significantly greater among those who received IVIG than among those who received placebo (1)

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Reference:

  • Aggarwal R et al. Trial of Intravenous Immune Globulin in Dermatomyositis N Engl J Med 2022; 387:1264-1278.