Characterization of Antinuclear, Myositis-Specific, and Myositis-Associated Antibodies in a Large Sample of Patients With Idiopathic Inflammatory Myopathies

Background: Antinuclear antibody (ANA) testing is routinely employed for screening systemic autoimmune diseases due to its accessibility and practicality. However, its diagnostic and clinical significance in idiopathic inflammatory myopathies (IIMs) remains uncertain. Therefore, this study aimed to determine the frequency and distribution of ANA, myositis-specific autoantibodies (MSAs), and myositis-associated autoantibodies (MAAs) in IIMs and to explore their interrelationships. Methods: In this single-center study, adult patients with definite IIMs were included. ANA was assessed by indirect immunofluorescence on HEp-2 cells, and MSA/MAA was analyzed using a commercial line blot assay, both performed at baseline. Results: Among 580 screened patients, 229 were excluded due to cancer-associated myositis (N=45), overlap myositis (N=21), unavailable serum samples (N=142), or missing ANA data (N=21). The final cohort included 351 patients, of whom 261 (74.4%) were ANA-positive (titers 1:80-1:1280). The predominant ANA pattern was isolated nuclear (61.7%), followed by cytoplasmic (18.0%) and nucleolar (6.9%). Multiple ANA patterns were observed in 13.4% of cases, while distinct patterns were identified in 34.1%. MSA and MAA were more frequently detected in ANA-positive patients, although they were also present in ANA-negative individuals. Conclusions: ANA positivity was observed in approximately three-quarters of IIM patients, exhibiting heterogeneous immunofluorescence patterns across subtypes. Although MSA and MAA were more common among ANA-positive individuals, their occurrence in ANA-negative patients highlights the necessity of combined testing approaches. These findings underscore the complementary roles of ANA and MSA/MAA assays in the comprehensive immunological evaluation of IIMs.