Positioning of myositis-specific and associated autoantibody (MSA/MAA) testing in disease criteria and routine diagnostic work-up.

Nowadays, the importance of detection of myositis-specific antibodies (MSA) and myositis-associated antibodies (MAA) in diagnosis and in delineating disease subsets of idiopathic inflammatory myopathy (IIM) is highly acknowledged by IIM experts. Consequently, MSA/MAA are increasingly integrated in expert-based myositis (sub)classification criteria as well as in routine diagnostics. In contrast, MSA/MAA are under-represented in data-based (sub)classification criteria, mostly related to the lack of sufficient data on the wide spectrum of MSA/MAA in large multicenter cohorts. Unfortunately, the current commercially available assays to detect MSA/MAA show variable analytical and clinical performance characteristics. This challenges the design of prospective multicenter studies on MSA/MAA as well as the optimization of their routine clinical use. Additional validation studies and continuous harmonization initiatives on MSA/MAA detection from the pre-analytical to the post-analytical phase (e.g. from defining request criteria to guidelines for reporting), will be needed to overcome these hurdles. To speed up this process, we encourage close collaborations between IIM clinical experts, laboratory professionals and diagnostic companies.