• disease activity
• treatment
• patient perspective

We read with great interest the extended report by Lilleker et al 1 on the EuroMyositis registry. Our attention was particularly addressed to antisynthetase syndrome (ASSD) because in the last years we and all members of the AENEAS (American and European Network of Antisynthetase Syndrome) collaborative group strongly contributed2–7 to increase the knowledge on this peculiar disease.

We think that a comparison between our cohorts could be of interest and useful for clinicians, even if the lack of some data in the EuroMyositis paper does not allow us to perform statistical analysis. Both groups collected a very large number of patients (AENEAS collaborative group 813 cases, EuroMyositis 512 cases). The comparison of available data seems to indicate that in the AENEAS and in the EuroMyositis cohort, patients’ age at disease onset (mean±SD: 51±14 vs 48±15 years), female sex (74% vs 69%), Raynaud’s phenomenon (RP) (44% vs 51%) and mechanic’s hands (37% vs 38%) prevalence are similar, whereas interstitial lung diseases (82% vs 71%) and, in particular, arthritis (68% vs 51%) seem to be more common in our cohort. However, these differences are intrinsic to our different politics: muscle involvement is the more common reason for patients’ inclusion in the EuroMyositis registry, whereas muscle involvement is not mandatory for the inclusion in our registry. Thanks to this choice, we showed that muscle involvement is not the most frequent onset finding in ASSD.2–4 6 In fact, in our cohort, 381 patients (47%) had no muscle involvement at disease onset and 186 (23%) were without muscle involvement and also without accompanying findings (RP, cutaneous manifestations and fever). On the other hand, we also showed that the occurrence of ex novo clinical findings during the follow-up is a typical hallmark of ASSD.2–6 However, the main problem that involves all groups working on ASSD is the lack of well-established clinicoserological classification criteria. This is not a secondary issue because patients with ASSD could be classified also as interstitial pneumonia with autoimmune features3 or, by considering clinical characteristics,4 6 8 as rheumatoid arthritis (RA),9 thus potentially entering in clinical trials addressed to other conditions. Also, the heterogeneity of commercially available testing tools, and the limited use of the gold-standard methodology, immunoprecipitation (IP), for antisynthetase antibodies (ARS) determination, add further variability in disease definition. In particular, IP is able to identify ARS positivity also when commercially available kits are negative.10 These considerations, together with the possible occurrence of other up to now not recognised ARS,11 suggest that the practice of defining ASSD based on simple positivity or negativity of these antibodies may lead to patients’ misclassification. In fact, we need classification criteria based on differential weights for various clinical, pathological and serological variables, such as that developed by the American College of Rheumatology and European League Against Rheumatism for RA.9 We think that this result will be achieved by the assessment of the steadily increasing number of patients with ASSD included in most recent reports. Thanks to the closer collaboration among the centres and groups interested in ASSD, the scientific community is now ready to work together to develop these much needed classification criteria.