Polymyositis

Key points

• 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