Polymyositis

Overview

• inflammatory disorder causing symmetrical, proximal muscle weakness
• thought to be a T-cellmediated cytotoxic process directed against muscle fibres
• may be idiopathic or associated with connective tissue disorders
• associated with malignancy
• dermatomyositis is a variant of the disease where skin manifestations are prominent, for example a purple (heliotrope) rash on the cheeks and eyelids
• typically affects middle-aged, female:male 3:1

Features

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

Investigations

• elevated creatine kinase
• EMG
• muscle biopsy
• anti-Jo-1 antibodies are seen in pattern of disease associated with lung involvement, Raynaud's and fever