A multiparameter EUROLINE blot for detection of myositis-related autoantibodies showed a high agreement with muscle biopsy results in patients with idiopathic inflammatory myopathies (IIM), suggesting it can be used as a first-line diagnostic tool in the diagnostic workflow. The recently published study was performed as part of a collaboration between scientists from EUROIMMUN Brazil and different universities in Brazil.
IIM are rare autoimmune diseases characterised by muscle weakness and inflammation. There are five subclasses of IIM which are differentially diagnosed based on clinical features, muscle biopsy analysis and autoantibody detection. The autoantibodies in IIM are divided into myositis-specific autoantibodies (MSA), which are specific for a particular subclass of IIM, and myositis-associated autoantibodies (MAA), which can be present in more than one subclass as well as in other conditions. Detection of MSA and MAA plays an important role in corroborating the final diagnosis in IIM patients. Of the various detection methods available, line blots allow easy accessibility as well as rapid and cost-reduced processing. The researchers therefore evaluated the performance and clinical applicability of a EUROLINE blot to support the diagnostic workflow. The study included patients with IIM diagnosed using muscle biopsy associated with clinical features as gold standard.
Samples from 50 patients with various forms of IIM (n=45) or other myopathies (n=5) were analysed using the EUROLINE Autoimmune Inflammatory Myopathies 16 Ag (IgG), which comprises the antigens Mi-2α, Mi-2β, TIF1γ, MDA5, NXP2, SAE1, Ku, PM-Scl100, PM-Scl75, Jo-1, SRP, PL-7, PL-12, EJ, OJ, and Ro-52. Samples were additionally analysed using an anti-HMGCR (IgG) line blot and an anti-cN-1A ELISA (IgG). All tests were from EUROIMMUN.
Myositis-related autoantibodies were detected in 74% (37/50) of the samples. MSA were present in 34 of these, and the remaining three samples contained only MAA. In 28 sera only one autoantibody was present, while nine samples showed co-positivity. In the 37 autoantibody-positive samples, the results were concordant with final diagnosis in 65% of cases, discordant in 16% and not evaluable in 19%. No MSAs were found in the patients with other myopathies. In 30% (15/50) of all cases, muscle biopsy analysis was essential to establish the final diagnosis.
The study demonstrated the good specificity of the autoantibody test panel, highlighting its applicability in the diagnostic workflow. The authors note that the study showed for the first time a 65% agreement between muscle biopsy findings and presence of autoantibodies. Line blots are less invasive than muscle biopsy, and the serological test could be used for initial screening in IIM in order to avoid an invasive procedure. In the proposed diagnostic flowchart, muscle biopsy analysis is not required in cases with MSA positivity, only in cases with MAA positivity alone or inconclusive or negative serology. Serological findings in combination with clinical characteristics can also guide therapeutic approaches, including malignancy screening and early management of interstitial lung disease.
Read more about the study
Fontana PN et al. Applicability of a serodiagnostic line blot for idiopathic inflammatory myopathy: the muscle biopsy is not all. Front. Neurol., 06 January 2025 doi.org/10.3389/fneur.2024.1504260