Abstract
Myositis-specific antibodies (MSA) and myositis-associated antibodies (MAA) are a feature of the idiopathic inflammatory myopathies (IIM), but are also seen in other rheumatic diseases, and in individuals with no clinical symptoms. The aim of this study was to assess the clinical utility of MSA and MAA and in particular the clinical relevance of weakly positive results. We included all patients at our institution who had at least one positive result on the Immunoblot EUROLINE myositis panel over a 6-year period (2015–2020). Associations with clinical features and final diagnosis were evaluated. Eighty-seven of 225 (39%) myositis panel tests met the inclusion criteria. There were 52 strong positives and 35 weak positives for one or more MSA/MAAs. Among the strong positive group, 15% (8/52) were diagnosed with IIM, 34.6% (18/52) with interstitial lung disease, 7.7% (4/52) with anti-synthetase syndrome, 25% (13/52) with connective tissue disease, and others accounted for 25% (13/52). In weak-positive cases, only 14% (5/35) had connective tissue disease and none had IIM. 60% (21/35) of weak-positive cases were not associated with a specific rheumatic disease. A significant number of positive myositis panel results, particularly weak positives, are not associated with IIM or CTD.
Highlights
The idiopathic inflammatory myopathies (IIM) are a heterogeneous group of autoimmune rheumatic diseases characterized by proximal muscle weakness and frequent involvement of other organ systems [1]
A total of 225 myositis panels were performed in the 6-year study period. 87/225 (39%) patients had positive myositis panel results and met the inclusion criteria, 39% were male and 61% female, with a mean (SD) age of 58 (+ -16) years
Our study shows that those with a strong positive myositis panel were more likely to be diagnosed with an IIM and were more likely to present with arthralgia
Summary
The idiopathic inflammatory myopathies (IIM) are a heterogeneous group of autoimmune rheumatic diseases characterized by proximal muscle weakness and frequent involvement of other organ systems [1]. The Bohan and Peter criteria were used for IIM, until 2017 when the European League Against Rheumatism and American College of Rheumatology (EULAR/ ACR) proposed new classification criteria [3, 4]. These new classification criteria reflect the advances of medicine in the last 40 years as well as providing higher performance (sensitivity/specificity, 93%/88% with biopsies, 87%/82% without biopsies). The criteria are in the form of a calculator which gives a probability score of the patient having myositis. A classification tree is used to help determine the subcategory (polymyositis (PM), dermatomyositis (DM), inclusion body myositis, and juvenile dermatomyositis) [4]
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