Muscle fiber ultrastructure is associated with the immunological profile in idiopathic inflammatory myopathies

The diagnosis and classification of Idiopathic Inflammatory Myopathies (IIM) remain complex because of the lack of information about their pathogeny. Scanning Electron Microscopy (SEM) allows a histological analysis with better resolution, which together with the immunological profile, is useful for a better understanding of physiopathology. For immunological profile characterization, we identified the presence of autoantibodies (Ro-52, OJ, EJ, PL7, PL12, SRP, Jo-1, PMScl75, PMScl100, Ku, SAE1, NXP2, MDA5, TIF1γ, Mi-2α, Mi-2β) and quantified cytokines (IL-1β, IFN-α2, IFN-γ, TNF-α, IL-6, IL-10, IL-12p70, IL-17A, IL-18, IL-23, IL-33) and chemokines (CCL2, CXCL8). The histological analysis was made by hematoxylin-eosin staining while the muscle fiber was characterized by SEM. We observed changes in the morphology and structure of the muscle fiber according to muscle strength and muscle enzymes. We were able to find and describe muscle fiber ultrastructure with marked irregularities, porosities, disruption in the linearity and integrity of the fascicle, more evident in patients with increased serum levels of muscle enzymes and diminished muscle strength. Even the scarce reports about the use of SEM as a tool in all clinical phenotypes of IIM, our work provides an excellent opportunity to discuss and reframe the clinical usefulness of SEM in the diagnostic approach of IIM.