Tuesday, 28 September 2010

MRCP revision battle 23.3: Polymyositis and Dermatomyositis

Polymyositis is an idiopathic inflammatory disorder of skeletal muscle.  When it is associated with cutaneous lesions it is dermatomyositis.

  • progressive proximal muscle weakness
  • dysphagia
  • interstitial lung disease
  • oesophageal dysfunction
  • weight loss 
  • fever
  • myocarditis
  • arthralgia

To try and remember this list I think of the condition starting in the proximal muscles of the arm then creeping to the joint (causing arthralgia) and onwards to the oesophagus, causing dysphagia and oesphageal dysfunction.  I then imagine it seeping into the lungs (interstitial lung disease) and then onwards into the heart (myocarditis).

Skin signs include:
  • heliotrope (liliac-purple) rash around eyelids/cheeks
  • macular rash over back and shoulders (=shawl sign)
  • Gottrons papules = scaly plaques on MCP/PIP joints
  • Gottrons sign = erythema over knees/elbows
  • periungal telangectasia
  • nail fold infarcts
  • photosensitivity

There is a higher prevalence of malignancy with dermatomyositis.

Investigations show:
  • raised CK/AST/LDH
  • abnormal EMG - shows fibrillation potentials
  • anti-Jo antibodies associated with a systemic form of disease

Treatment is:
  • prednisolone
  • methotrexate
  • screen for maligancy.

NB: juvenile dermatomyositis is different - it is more aggressive and includes a vasculitis and ectopic calcification.

Now onwards for our first expedition into the world of sexually transmitted diseases...