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The presence of muscle weakness and anti-Jo1 anti-aminoacyl transfer RNA synthetase (ARS) autoantibodies are evaluated in the new European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) proposed classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIM), as well as in the Solomon proposed criteria for antisynthetase syndrome (ASSD) diagnosis.1 2 That favours an overlapping in both criteria fulfilment; however, ASSD is not considered among the IIM subgroups classification.
Anti-Jo1 ARS positivity is the highest weighted criterion in the EULAR/ACR criteria. Furthermore, anti-PL7 and anti-PL12 ARS were found to be strongly associated with IIM during the criteria development; however, the low number of observations limited their reliability analysis, and they were not finally included.1 3 Anti-EJ, anti-OJ and other ARS were not considered at all due to the limited availability of detection methods at the start of the criteria development.3 On the other hand, any ARS positivity is considered in Solomon’s criteria.
Thus, according to other authors, we purpose that IIM and ASSD classification criteria might need a revision to better homogenise patient groups.3–6 Therefore, we designed this study to evaluate if the detection of ARS other than anti-Jo1 could improve the EULAR/ACR criteria performance, and additionally to contribute to a better classification of the antisynthetase syndromes.
We retrospectively analysed a cohort of 37 patients with clinical suspicion of IIM or ASSD and positive ARS in the myositis immunoblot. The main objectives were to assess: (1) the rate of patients meeting EULAR/ACR and Solomon’s criteria; (2) the rate of patients with anti-Jo1 and with non-anti-Jo1 ARS that fulfilled them; and (3) the rate of patients with non-anti-Jo1 ARS meeting the EULAR/ACR criteria if we assign to these antibodies the same weight as anti-Jo1 ARS. For information about data source, statistical analysis and characteristics of the study population, see online supplementary text and online supplementary Table S1.
As a result, 22 patients (59.5%) met EULAR/ACR criteria (13 probable and 8 definitive) and 17 patients (45.9%) met Solomon’s criteria. When analysing the compliance of them together, we found that 13 patients (35.1%) fulfilled both criteria, representing the 59.1% of those patients who met EULAR/ACR criteria and the 76.5% of those who met Solomon’s criteria.
Analysing by antibodies, all patients with anti-Jo1 ARS (n=17) met EULAR/ACR criteria (11 probable and 6 definitive). Among the patients with non-anti-Jo1 ARS (n=20), only 5 (25%) met the criteria (2 probable and 3 definitive); however, if we gave the anti-Jo1 weight to the other ARS when applying the EULAR/ACR criteria, 19 of the 20 cases (95%) would meet them (7 probable and 12 definitive) (table 1). Besides, considering the clinical features, 10 of the 20 patients with non-anti-Jo1 ARS (50%) presented clinically objectified muscle weakness, and only 4 of them met EULAR/ACR criteria; nevertheless, weighing any ARS as anti-Jo1, the other six cases would be reclassified as IIM.
In summary, we have observed that a high rate of patients with clinical suspicion of IIM or ASSD and positive ARS fulfilled EULAR/ACR and also Solomon’s criteria; and that all cases with anti-Jo1 positivity met EULAR/ACR criteria, but not those with other ARS. Additionally, when we applied the EULAR/ACR criteria assigning to all ARS the same weight as anti-Jo1, all except one patient fulfilled the criteria; thus, the most important result was that all patients with clinically objectified muscle weakness and non-anti-Jo1 ARS that initially did not meet the EULAR/ACR criteria could be re-classified as IIM.
To conclude, the main limitations of this study are the retrospective design, the relatively small size of the sample and the absence of a comparator group. However, it suggests that the detection of non-anti-Jo1 ARS in patients with myopathy suspicion could increase the sensitivity of the EULAR/ACR classification criteria; and that the ASSD, when presents myositis, should be considered among the IIM classification subgroups.
1) Dr Juan Carlos Quevedo Abeledo, Rheumatology Department, Hospital Universitario de Gran Canaria Dr Negrín, Las Palmas, Spain. 2) Dr Carlos Rodríguez-Lozano, Rheumatology Department, Hospital Universitario de Gran Canaria Dr, Negrín, Las Palmas, Spain. 3) Dr Francisco Rubiño Juarez, Rheumatology Department, Hospital Universitario de Gran Canaria Dr, Negrín, Las Palmas, Spain. 4) Dr Juan Manuel Díaz, Biochemical Department, Autoimmunity Laboratory, Hospital Universitario de Gran Canaria Dr, Negrín, Las Palmas, Spain. 5) Spanish Society of Rheumatology.
Handling editor Josef S Smolen
Contributors MG: study design, data management, analysis, interpretation, verification, writing. MJGdY: study design, analysis, verification, interpretation. IA: data management, interpretation. AMB-G: data management, interpretation. IR-F: data management, interpretation, writing. EL: interpretation, writing. LC: study design, verification, interpretation, writing.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval Ethical approval for this study was obtained from the ethical committee of the Hospital Universitario de Gran Canaria Dr. Negrín (code 2018-222-1).
Provenance and peer review Not commissioned; externally peer reviewed.