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Abstract

Objective

Previous case series have examined the relationship between anti–Jo-1 antibody levels and myositis disease activity, demonstrating equivocal results. Using enzyme-linked immunosorbent assays (ELISAs) and novel measures of myositis disease activity, the current study was undertaken to systematically reexamine the association between anti–Jo-1 antibody levels and various disease manifestations of myositis.

Methods

Serum anti–Jo-1 antibody levels were quantified using 2 independent ELISA methods, while disease activity was retrospectively graded using the Myositis Disease Activity Assessment Tool, which measures disease activity in 7 different organ systems via the Myositis Disease Activity Assessment Visual Analog Scale (VAS) and the Myositis Intention-to-Treat Index (MITAX) components. Spearman's rank correlation coefficients and mixed linear regression analysis were used to identify associations between anti–Jo-1 antibody levels and organ-specific disease activity in cross-sectional and longitudinal analyses, respectively.

Results

Cross-sectional assessment of 81 patients with anti–Jo-1 antibody revealed a modest correlation between the anti–Jo-1 antibody level and the serum creatine kinase (CK) level, as well as muscle and joint disease activity. Correlation coefficients were similar for CK levels (rs = 0.38, P = 0.002), myositis VAS (rs = 0.36, P = 0.002), and arthritis VAS (rs = 0.40, P = 0.001). In multiple regression analyses of 11 patients with serial samples, anti–Jo-1 antibody levels correlated significantly with CK levels (R2 = 0.65, P = 0.0002), myositis VAS (R2 = 0.53, P = 0.0008), arthritis VAS (R2 = 0.53, P = 0.006), pulmonary VAS (R2 = 0.69, P = 0.005), global VAS (R2 = 0.63, P = 0.002), and global MITAX (R2 = 0.64, P = 0.0003).

Conclusion

In this large series of patients with idiopathic inflammatory myopathy, anti–Jo-1 antibody levels correlated modestly with muscle and joint disease, an association confirmed by a custom ELISA using recombinant human Jo-1. More striking associations emerged in a smaller longitudinal subset of patients that link anti–Jo-1 antibody levels to muscle, joint, lung, and global disease activity.