Inflammatory disorder causing symmetrical, proximal muscle weakness
thought to be a T-cell mediated 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

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

Laboratory investigations

elevated creatine kinase
anti-Jo-1 antibodies - associated with ILD, Raynaud's and fever

Other investigations

muscle biopsy

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