MHC class I expression is a characteristic histopathological feature of myositis, and seems to correlate with the presence of muscle weakness both in patients and in an animal model of myositis.

The distribution of IIM subtypes showed dermatomyositis as the most common (78.9%), followed by polymyositis (57.9%), inclusion body myositis (15.8%), and immune-mediated necrotizing myopathy (5.3%).