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

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.