polymyositis and dermatomyositis

Last edited 07/2023 and last reviewed 07/2023

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.

Clinical features of dermatomyositis include:

• possible dermatological features include
  • a heliotrope rash (a red-to-violet - colored rash around the eyes that might be accompanied by swelling)
  • Gottron papules (red bumps most prominently seen on the knuckles of the hands)
  • other characteristic dermatological findings include:
    • red purplish discoloration on the face, exposed surfaces of the arms, forearms and hands, scalp, upper chest, upper back (known as a Shawl sign), and the lateral hips (known as the holster sign) in addition to changes around the cuticles of the fingernails
    • photosensitivity may occur (1)
• myopathic symptoms
  • muscle inflammation tends to affect larger muscles and can present as difficulty raising the arms above the shoulder or trouble rising from a chair or climbing stairs (1)
  • occasionally there is muscle tenderness, fatigue, and low-grade fever
• dermatomyositis can also affect the oesophagus, lungs, or heart

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 (2)

Click here for example images of this condition

Reference:

• Callen JP. Dermatomyositis. JAMA Dermatol. Published online July 05, 2023. doi:10.1001/jamadermatol.2023.1013
• Aggarwal R et al. Trial of Intravenous Immune Globulin in Dermatomyositis N Engl J Med 2022; 387:1264-1278.