Purpose of review: To review recent advances in immunopathology for idiopathic inflammatory myopathies, focusing on widely available immunohistochemical analyses.
Recent findings: Sarcoplasmic expression of myxovirus resistance protein A (MxA) is specifically observed in all types of dermatomyositis and informs that type I interferons are crucially involved in its pathogenesis. It is a more sensitive diagnostic marker than perifascicular atrophy. Diffuse tiny dots in the sarcoplasm highlighted by p62 immunostaining are characteristically seen in immune-mediated necrotizing myopathy. This feature is linked to a chaperone-assisted selective autophagy pathway. Myofiber invasion by highly differentiated T cells, a marker of which is KLRG1, is specific to inclusion body myositis and has a crucial role in its pathogenesis. The recent advances in immunopathology contribute to increased diagnostic accuracy and a better understanding of the underlying pathophysiology in different types of idiopathic inflammatory myopathies.
Keywords: Immunohistochemistry; KLRG1; Membrane attack complex; Muscle pathology; MxA; p62.