Objective:
To analyze the frequencies of the expression of major histocompatibility complex class I (MHC-I) antigens, and CD4 and CD8 cells in skeletal muscle in polymyositis (PM) and dermatomyositis (DM).
Methods:
This was a retrospective study of 34 PM cases, 8 DM cases, and 29 control patients with non-inflammatory myopathies.
Results:
MHC-I antigens were expressed in the sarcolemma and/or sarcoplasm in 79.4% of PM cases, 62.5% of DM cases, and 27.6% of controls (CD4 expression was observed in 76.5%, 75%, and 13.8%, respectively). There was a high suspicion of PM/DM (mainly PM) in participants in whom MHC-I antigens and CD4 were co-expressed. In 14.3% of PM/DM cases, we observed MHC-I antigens expression alone, without inflammatory cells.
Conclusion:
MHC-I antigens expression and CD4 positivity might add to strong diagnostic suspicion of PM/DM. No cellular infiltration was observed in approximately 14.3% of such cases.
Muscle pathology; Muscle immunohistochemistry; Muscle biopsy; Major histocompatibility complex class I antigens (MHC-I); Inflammatory myopathies
