Dermatomyositis an inflammatory disorder causing symmetrical, proximal muscle weakness and characteristic skin lesions.


  • Incidence: 1.00 cases per 100,000 person-years
  • Peak incidence: 50-60 years
  • Sex ratio: more common in females 2:1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+


  • may be idiopathic or associated with connective tissue disorders or underlying malignancy (typically ovarian, breast and lung cancer, found in 20-25% - more if patient older). Screening for an underlying malignancy is usually performed following a diagnosis of dermatomyositis
  • polymyositis is a variant of the disease where skin manifestations are not prominent

Clinical features

Skin features
  • photosensitive
  • macular rash over back and shoulder
  • heliotrope rash in the periorbital region
  • Gottron's papules - roughened red papules over extensor surfaces of fingers
  • 'mechanic's hands': extremely dry and scaly hands with linear 'cracks' on the palmar and lateral aspects of the fingers
  • nail fold capillary dilatation

Other features
  • proximal muscle weakness +/- tenderness
  • Raynaud's
  • respiratory muscle weakness
  • interstitial lung disease: e.g. Fibrosing alveolitis or organising pneumonia
  • dysphagia, dysphonia


  • the majority of patients (around 80%) are ANA positive
  • around 30% of patients have antibodies to aminoacyl-tRNA synthetases (anti-synthetase antibodies), including:
    • antibodies against histidine-tRNA ligase (also called Jo-1)
    • antibodies to signal recognition particle (SRP)
    • anti-Mi-2 antibodies

Creatine kinase is elevated.

Skin and muscle biopsies may be done to confirm the diagnosis.

  • useful in distinguishing myopathy from neuropathy


  • prednisolone