Dermatomyositis

Overview

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

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

Investigations

• the majority of patients (around 80%) are ANA positive