Serum Jo-1 Autoantibody and Isolated Arthritis in the Antisynthetase Syndrome: Review of the Literature and Report of the Experience of AENEAS Collaborative Group.

Anti-Jo-1 is the most frequently detectable antibody in the antisynthetase syndrome (ASSD), an autoimmune disease characterized by the occurrence of arthritis, myositis, and interstitial lung disease (ILD). Recently, we organized an international collaborative group called American and European NEtwork of Antisynthetase Syndrome (AENEAS) for the study of this rare and fascinating disease. The group collected and published one of the largest series of ASSD patients ever described and with one of the longer follow-up ever reported. The number of participating centers is steadily increasing, as well as the available cohort. In the first paper, we showed that arthritis, myositis, and ILD may be frequently the only feature at disease onset, raising problems to reach a correct diagnosis of this syndrome. Nevertheless, we first observed that the ex novo appearance of further manifestations is common during the follow-up, strengthening the importance of a correct diagnosis. In our cohort, the 24 % of the 243 patients up to now collected had isolated arthritis as a presenting feature. These patients represent the most intriguing group in terms of differential diagnosis and clinical time course. Furthermore, data on this aspect are scanty, the reason that lead us to evaluate these aspects in our cohort of patients, reviewing also available literature. In fact, the most relevant aspect is that ASSD is rarely suspected in this setting of patients, in particular in case of poliarticular involvement, positive rheumatoid factor (RF), or anti-cyclic citrullinated peptide antibodies (ACPA) or evidence of joint erosions at plain radiographs. These findings were not rare in our cohort, and they have been also described in other series. Furthermore, manifestations such as Raynaud's phenomenon, mechanic's hands, and fever that may lead to the suspect of ASSD are observed only in a third of cases. If we consider the high rate of clinical picture progression in these patients, we feel that ASSD should be carefully considered in all patients presenting with isolated arthritis, even in those with erosive, RF, and ACPA-positive arthritis.