Detection of multiple myositis-specific antibodies: prevalence and clinical significance

Abstract Background The multipositivity of myositis-specific antibodies (MSAs) is uncommon. Our study aimed to assess the prevalence and the clinical relevance of multiple positive MSAs in routine practice. Methods A 10 year single-center retrospective study (2015-2024) was conducted reviewing all samples analyzed with the Dot Myositis EUROLINE (Euroimmun Germany). Clinical data corresponding to samples with multiple positive MSAs was reviewed. Results Among 140 samples positive for at least 1 MSA, 22 patients (15.7%) were positive for at least 2 MSAs on the same sample. The diagnosis of idiopathic inflammatory myopathies (IIMs) was confirmed in only 6 patients (27.2%). The frequency of double-positive MSAs was 100% in IIM patients and 60% in non-IIM patients. No IIM patients and 40% of non-IIM patients (P = .037) had 3 or more positive MSAs. MSA titers were higher in IIM patients than in non-IIM patients (49 vs 32 AU, P = .33). The clinical IIM subtype joined the IIM subtype corresponding to the predominant MSA. We had no mixed features of either IIM subtype or added severe prognosis. Conclusion Detection of multiple MSAs is uncommon but possible using immunodot techniques. Taking into account MSA number, level of positivity, and clinical data helps in the interpretation of the results.