The antisynthetase syndrome (ASS) is clinically characterized by fever, myositis, interstitial lung disease, joint involvement, mechanic’s hands, or Raynaud’s phenomenon, and the presence of antisynthetase autoantibodies. These clinical manifestations may not occur simultaneously. Therefore, the aim of this study was to analyze the sequence in which these clinical manifestations can develop at the onset of ASS. This retrospective, single-center cohort study enrolled 55 ASS patients. Their mean age at the onset of ASS symptoms was 42.3±11.8 years. There was a predominance of female patients (75.9%) and white patients (72.7%). At initial presentation, 41.8% of the patients had fever, 43.6% had joint symptoms, 38.2% had myositis, 36.4% had interstitial lung disease, 18.2% had Raynaud’s phenomenon, and 16.4% had mechanic’s hands. Subsequent clinical symptoms emerged at varying time points. In two out of 55 cases, joint, muscle, and lung manifestations developed simultaneously. The median time between the onset of symptoms and the complete ASS clinical manifestation was 19.9 (4.0-60.2) months; whereas, the timeframe between the onset of symptoms and the ASS diagnosis was 29.0 (11.0-63.0) months. The confounding misdiagnoses interfering with the initial diagnosis were polymyositis (52.7%), dermatomyositis (29.1%), nonspecific interstitial pneumopathy (23.6%), rheumatoid arthritis (18.2%), and others (10.9%). Clinical features at the onset of ASS are highly variable. Consequently, confounding factors can lead to significant delays for the final and definitive diagnosis of ASS. Therefore, ASS should be considered a differential diagnosis in patients with initial symptoms of joint, lung, and/or muscle involvements, as well as fever, mechanic’s hands, and/or Raynaud’s phenomenon manifestations.

Background The protein chitinase-3-like-1 (YKL-40) is rarely analyzed in patients with myositis. Therefore, we aimed to evaluate YKL-40 serum levels; correlate them with laboratory and clinical parameters, disease status, and treatment schemes; and analyze the YKL-40 expression in the muscle tissues of patients with antisynthetase syndrome (ASSD). Methods This cross-sectional single-center study included 64 adult patients with ASSD who were age-, gender-, and ethnicity-matched to 64 healthy control individuals. Their YKL-40 serum levels were analyzed using the Enzyme-Linked Immunosorbent Assay (ELISA) kit method, while YKL-40 expression in muscle tissues was analyzed using an immunohistochemical technique. Disease status was assessed using the International Myositis Assessment and Clinical Studies Group (IMACS) set scores. Results The patients’ mean age was 44.8 ± 11.8 years, and median disease duration was 1.5 (0.0–4.0) years. These patients were predominantly female (82.8%) and Caucasian (73.4%). Most patients had stable disease. The median YKL-40 serum level was significantly higher in patients with ASSD when compared to the healthy individuals: 538.4 (363.4–853.1) pg/mL versus 270.0 (201.8–451.9) pg/mL, respectively; P < 0.001. However, YKL-40 serum levels did not correlate with any clinical, laboratory, disease status, or therapeutic parameters (P > 0.050), except tumor necrosis factor alpha (TNF-α) serum levels (Spearman’s correlation, rho = 0.382; P = 0.007). YKL-40 was highly expressed by inflammatory cells found in muscle biopsy specimens. Conclusions High YKL-40 serum levels were observed in patients with ASSD and correlated positively with TNF-α serum levels. Moreover, YKL-40 was expressed by the inflammatory cells of the muscle tissue.

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