Classification

Dermatomyositis is subclassified into five types by some authors:

• adult polymyositis - without skin involvement
• adult dermatomyositis
• polymyositis or dermatomyositis with malignancy
• childhood dermatomyositis
• polymyositis or dermatomyositis associated with other immunologic disorders such as systemic lupus erythematous, systemic sclerosis, Sjogren's syndrome

The approach taken here has been to describe the adult form of dermatomyositis and mention the unique features found in children since these are the two most important categories from a clinical perspective.

In practise, there is increasing evidence that polymyositis and dermatomyositis are distinct diseases:

• polymyositis tends to have a chronic natural history and is less responsive to therapy
• dermatomyositis can be life-threatening, but is more responsive to treatment