Dermatomyositis

Dermatomyositis is an inflammatory condition resulting in symmetrical proximal muscle weakness and skin lesions. 

  • Dermatomyositis is idiopathic in most cases. 
  • However, it is important to note that it may indicate an underlying malignancy in as many as 25% of patients -  ovarian, breast, lung 

Clinical features

Cutaneous features - 'Dermato...'

  • Heliotrope periorbital rash - redish/purple rash on eyelids
  • Red macular rash affecting back and shoulders
  • Mechanics hands – Gottron’s red papules on extensor surfaces - often overlying the knuckles and PIP/DIP joints
  • Rashes are photosensitive

‘Myositis..’

  • Symmetrical, proximal weakness +/- tenderness
    • Difficult climbing stairs, getting up from chair, holding up a cup of tea or brushing hair etc. 

General symptoms

  • Fatigue
  • Weight loss
  • Night sweats 

Other features: ILD causing shortness of breath, Raynaud’s phenomenon 

Figure 223: Heliotrope rash in dermatomyositis; violaceous to erythematous discrete or confluent macules confined to the upper eyelids. Elizabeth M. Dugan, Adam M. Huber, Frederick W. Miller, Lisa G. Rider, CC BY-SA 3.0.
Figure 224: Gottron's papules in a patient with juvenile dermatomyositis. Elizabeth M. Dugan, Adam M. Huber, Frederick W. Miller, Lisa G. Rider, CC BY-SA 3.0
Figure 224: Gottron's sign. Confluent macular erythema with scale confined to the skin overlying the patellae in a girl with juvenile dermatomyositis. Elizabeth M. Dugan, Adam M. Huber, Frederick W. Miller, Lisa G. Rider, CC BY-SA 3.0.

Investigations

Bloods

  • Raised CK due to myositis
  • ANA positive (80%)
  • Antibodies:
    • Anti-MI-2 Antibodies
    • Anti-SRP antibodies
    • (Anti-Jo 1 antibodies - more associated with polymyositis) 

Management

  • Steroids - Prednisolone 
  • Patients should be screened for malignancy

Polymyositis

  • A variant of dermatomyositis without skin manifestations
  • Clinical features:
    • Symmetrical, proximal weakness +/- tenderness
      • Difficult climbing stairs, getting up from chair, holding up a cup of tea or brushing hair etc. 
  • Investigations:
    • Raised CK due to myositis
    • Antibodies: Anti-JO1 (vs histidine tRNA ligase)