Last reviewed 10/2022

Dermatomyositis and polymyositis are ischaemic myopathies resulting from capillary obliteration and consequent muscle infarction.

Muscle biopsy shows an inflammatory cell infiltrate:

  • in dermatomyositis these cells are predominantly B lymphocytes with some T-helper lymphocytes - suggesting a humoral autoimmune mechanism

  • in polymyositis the cells are mainly cytotoxic T cells - suggesting a cell-mediated autoimmune mechanism