Statistics from Altmetric.com
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.
The publication of the EULAR/ACR classification criteria for ‘idiopathic inflammatory myopathy’ group of disease would be considered a landmark work in this field.1 The tremendous efforts of a large number of dedicated workers in the field of myositis from around the world coming together to produce this seminal document deserve high praise. The hope is that it will aid the drug trials on homogeneous subsets of this group of diseases yielding meaningful results. However, there is some concern for ‘an outsider’, a general rheumatologist like me, for not putting more emphasis on myositis-specific antibodies (MSAs). Most of the authors of this document have dedicated their careers to the discovery of MSAs. These are the same authors who have widely reported the clinical importance of the MSAs, their effect on the clinical features, clinical course as well as on the treatment response. Yet, they seem to have shied away from including MSAs in this classification (except anti-Jo1 antibody). It is from the publications of these reputed workers that we have learnt the importance of MSAs and how they define the clinical features, disease course and the response to treatment. Thus, we have learnt that there are mainly four subgroups that present as amyopathic dermatomyositis (ADM): those who are positive for anti-histidyl tRNA synthetase (anti-Jo-1), anti-non-Jo1, anti-melanoma differentiation-associated gene 5 (anti-MDA5) and anti-transcription intermediary factor-1 gamma (TIF-1γ) MSAs. Simply categorising a patient as ‘ADM’ and only testing for anti-Jo-1 autoantibody but not for anti-non-Jo-1, anti-MDA5 and TIF-1γ, might be problematic. The latter three categories are very different in their clinical involvements, response to treatment and outcomes. Any drug trial in this group of mixed patients would, therefore, fail to yield meaningful results. Similarly, we have learnt that there are four subgroups of patients who present with pathognomonic dermatomyositis rash and would get classified under ‘DM’. Without screening for MSAs, one would not be able to distinguish between the four subgroups, namely, anti-nucleosome-remodelling deacetyalse complex (anti-Mi2) antibody, anti-small ubiquitin-like modifier activating enzyme (anti-SAE) antibody, anti-TIF-1γ antibody and anti-nuclear matrix protein 2 (NXP2) antibody syndromes. Many publications have shown that their clinical course and outcome with treatment are very different. Conducting drug trials in such a heterogeneous group would yield confusing results. A similar problem would arise in the group that would be classified as polymyositis. As we have learnt, if patients in this subgroup are screened for MSAs, the majority would be negative for autoantibodies. However, there would also be patients with anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCoAR), anti-signal recognition particle (anti-SRP), anti-survival of motor neuron complex (anti-SMN) and anti-four-and-a-half LIM domain 1 (anti-FHL1) autoantibodies, each with different response to any form of treatment, that would muddle the results of any drug trial. Maybe it is rather naive for a ‘general rheumatologist’ to ask these questions. However, the response of the experts may help us understand this field better. As is mentioned in the document, this classification is ‘provisional’. Maybe this international group of workers is already at an advanced stage of developing MSA-based/inclusive classification criteria for idiopathic inflammatory myopathies.
Competing interests None declared.
Provenance and peer review Not commissioned; internally peer reviewed.