Overview Polymyositis (PM) and dermatomyositis (DM)

Polymyositis (PM) and dermatomyositis (DM) are ‘autoimmune’ conditions. This means that the immune system – which usually protects the body against infection/germs – becomes overactive and starts attacking the body’s own tissues rather than protecting them.

PM and DM are part of a range of conditions known as myositis-spectrum disorders, which also include necrotising myositis and anti-synthetase syndrome. The key feature linking these conditions together is ‘myositis’ – this means inflammation of the muscles, which can lead to weakness of the arms and legs.

DM occurring in childhood may have important differences – please see our information about juvenile dermatomyositis to find out more about the childhood form of DM.

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