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