Muscle mitochondrial changes in antisynthetase syndrome and other idiopathic inflammatory myopathies.

Mitochondria are critical for cellular function. Their dysfunction contributes to cell degeneration and death, leading to disease progression. This study examined mitochondrial changes in idiopathic inflammatory myopathies (IIMs) including antisynthetase syndrome (ASyS), dermatomyositis (DM), and inclusion body myositis (IBM). Skeletal muscle biopsies were analyzed using histology, histochemistry, and electron microscopy from patients diagnosed with IIMs, according to the clinico-sero-morphological classification. There was no significant age difference between 16 ASyS and 16 DM patients, but 11 IBM patients were significantly older. The ASyS group had higher serum creatine kinase levels and showed prominent mitochondrial abnormalities similar to IBM and greater than the DM group. While all IIM groups displayed conventional mitochondrial changes, including ultrastructural abnormalities with cristae alterations, paracrystalline inclusions were exclusive to IBM and ASyS. There were significantly more rod-like filamentous inclusions adjacent to mitochondria in the IBM and ASyS groups, compared to the DM group. Intra-mitochondrial filament aggregates with focal formation of inclusions were also identified in individual ASyS and IBM patients, suggesting a link between the mitochondrial filamentous inclusions and nuclear and/or cytoplasmic filamentous inclusions. These findings suggest that mitochondrial abnormalities, particularly in ASyS and IBM, may contribute to the pathogenic process and clinical manifestations of the disease.