• inflammation
• autoantibodies
• treatment

We have with great interest read the response letter by Dr Infantino and colleagues on testing of methodologies used for detection of myositis-specific antibodies (MSA), to be published in the Annals of the Rheumatic Diseases.1 The authors discuss the need for validation of methodologies used for identifying MSA. The discussion stems from the publication of the new classification criteria for idiopathic inflammatory myopathies (IIM) ‘2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups’ that include one MSA, the anti-Jo1 antibody.2

We agree with the authors that validation of the commercially available tests for MSA is of utmost importance and that this work should include all relevant stakeholders: clinicians, clinical laboratories actually performing the analyses as well as the diagnostic industry. We also believe that harmonisation and standardisation of actual assay implementation should be part of this discussion. Related to this, we also fully agree with Mahler and Fritzler3 that the issue of internal antibody-specific controls and calibration of these assays should be addressed. Moreover, from a clinical point of view, we think that assay results should be interpreted in relation to longitudinally collected clinical data. The steering committee of the Euromyositis register has long been working on standardisation and systematic analyses of autoantibodies. Autoantibody data are recorded in the register (www.euromyositis.eu) along with clinical data, and will be an important source for a future update of classification criteria for IIM, as well as to increase our knowledge of associations between autoantibody positivity and clinical phenotype, disease progression and response to treatment. A prerequisite for the legitimacy of this work is the use of validated antibody assays. The line immunoassay has the advantage of being a fast and easy method that can be used routinely, but the new antibody specificities still need to be validated against immunoprecipitation and in relation to clinical cohorts with differential diagnoses. We therefore encourage all initiatives aimed at increasing our understanding of the role of MSA, as well as the accuracy of methods used for their detection. Inevitably, an international collaborative approach is needed. We believe that the Euromyositis register, including more than 5000 patients with IIM and involving 23 clinics worldwide, provides an appropriate foundation for this type of work, but will also need to include the manufacturers of the immunoassays in question.

We welcome collaborations with myositis experts in this work towards systematic and harmonised collection of autoantibody data in patients with IIM using validated immunoassays together with longitudinal clinical data.