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Response to: '2017 EULAR/ACR classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups: little emphasis on autoantibodies, why?' by Malaviya
  1. Ingrid E Lundberg,
  2. Anna Tjärnlund
  1. Rheumatology Unit, Department of Medicine, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden
  1. Correspondence to Profossor Ingrid E Lundberg, Rheumatology Unit, Department of Medicine, Karolinska University Hospital, Karolinska Institutet, Solna, Stockholm S-171 76, Sweden; ingrid.lundberg{at}ki.se

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We are grateful for the insightful and highly relevant question raised by Dr Malaviya1 concerning the 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups. The question concerns autoantibodies, and in particular myositis-specific autoantibodies (MSAs), and why only the anti-Jo-1 autoantibody is included in the new classification criteria.

We understand the concern that was raised and we have discussed the limitation of having limited data on MSAs in our publication.2 This letter gives us a possibility to expand on this limitation and include some more explanations. Our study was initiated more than 10 years ago, and during the last decade we have seen a great advancement in the knowledge of autoantibodies specific for and associated with idiopathic inflammatory myopathies (IIM). This includes identification of several new MSAs, as well as advancement in methods used to detect MSAs that have made it possible to test most of the MSAs in clinical practice by commercially available assays. Unfortunately, these assays were not available for most of the MSAs at the time of data collection for our project. Indeed, as pointed out by Dr Malaviya, an increasing knowledge has emerged concerning associations between presence of autoantibodies and clinical phenotype, disease progression and response to treatment, emphasising the importance of the MSAs in clinical practice and classification. The data on autoantibody profiles included in the data set of this study conducted at 47 clinics worldwide reflect the limited availabilities of detection methods for MSAs at the start of the study. Due to this we had data for only five MSAs included in the study. We found a strong association between all of them and cases being classified as IIM. However, only the anti-Jo-1 autoantibody reached sufficient number of observations (n=1062) in cases and comparators for valid inclusion in the classification criteria. In the manuscript we addressed the need for inclusion of more autoantibody data in a future update of the criteria.

It took many years to collect patient data for the myositis criteria project to include the number needed of cases and comparators cases, adults and children, representing different centres and different ethnicities. During these years we have seen scientific advances in myositis and development of several collaborative networks that will facilitate update of the criteria. One such international collaborative effort is the international, multidisciplinary myositis register, Euromyositis, currently including more than 4000 patients with IIM and involving 23 clinics worldwide. The steering committee of the Euromyositis register has long been working on standardisation of sample collection and assessment of autoantibodies for inclusion in the register. Data from this register can be one source for a future update of the classification criteria, but other cohorts are needed, including comparator cases where MSAs have been tested. The assessment of MSAs using validated methods will be of utmost importance for use in classification criteria development. We will then have the possibility to address the value of MSAs for classification of IIM, as well as to test association of certain autoantibodies with different clinical phenotypes, disease progression and response to treatment. This will enable us an even better subclassification of IIMs that will ultimately pave the way for clinical trials with relevant and homogeneous patient groups and hopefully development of improved treatment for these patients.

Dr Malaviya is correct that the classification criteria are provisional. As stated by the European League Against Rheumatism and the American College of Rheumatology, ‘This signifies that the criteria set has been quantitatively validated using patient data, but it has not undergone full validation based on an independent dataset, using both cases and controls. This validation step is still needed before the criteria are fully validated’. Hence the term provisional refers to the need of validation of the criteria in an independent cohort including both cases and controls, but does not imply that the criteria items included are non-significant or not important. We welcome collaboration with experts who have access to such cohorts as a next step for an external validation of the new criteria.

We hope that we have addressed the concern raised by Dr Malaviya by this response and we welcome initiatives to perform external validation of the ‘European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups’, as well as testing the whole panel of MSAs both for classification of IIM and for classification of subgroups of IIM. Only a systematic and harmonised collection of autoantibody data using validated antibody assays together with clinical data in a large international, multidisciplinary collaboration will make future revision of these novel classification criteria possible.

References

Footnotes

  • Competing interests None declared.

  • Provenance and peer review Commissioned; internally peer reviewed.

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