High prevalence of necrotising myopathy pattern in muscle biopsies of patients with anti-Jo-1 antisynthetase syndrome.

Objectives: Until now, researchers have not provided a well-defined muscle histological pattern for antisynthetase syndrome (ASSD). Therefore, we aimed to analyse the muscle biopsies of patients with anti-Jo-1 ASSD.

Methods: This study included 26 patients with anti-Jo-1 ASSD admitted for investigation of the disease and obligatorily with muscle impairment, from 2010 to 2021, whose serial frozen muscle sections were analysed.

Results: Patients' mean age at disease diagnosis was 42.8±11.6 years, and the female gender was most predominant. Concerning muscle biopsies, cell infiltrates were present in 76.9% of the samples, and they were mainly located at the endomysium area (70%), with a predominance of macrophages (92.9%). Fiber muscle necrosis was present in 92.3% and was diffused in 54.2%. Expression of MHC-I was seen in all samples. Samples were mostly marked by the presence of CD68+ and discreet/low CD4+ and CD8+ staining, which is consistent with a higher predominance of observed necrosis and macrophage cell infiltrates. In general, 38.5% of patients had a necrotising myopathy pattern in muscle biopsies, whereas 34.6% and 26.9% had a general inflammatory myopathy pattern and nonspecific myopathy, respectively. This necrotising myopathy pattern was not associated with the demographic, clinical, or laboratory data.

Conclusions: Our data show that almost 40% of patients with well-defined anti-Jo-1 ASSD with objective muscle impairment have a necrotising myopathy pattern in their muscle biopsies. Although this pattern is more classically related to immune-mediated necrotising myopathies, in association with clinical manifestations and the presence of anti-Jo-1 autoantibodies, this characteristic may lead to ASSD diagnosis.