Myositis
Abstract Number 1647 - Anti-Jo-1 Antibody Levels Correlate with Muscle and Articular Disease Activity in Idiopathic Inflammatory Myopathy
Authors: K. B. Stone, C. V. Oddis, N. Fertig, Y. Katsumata, M. Lucas, M. T. Vogt, D. P. Ascherman. University of Pittsburgh School of Medicine, Pittsburgh, PA
PURPOSE: The aim of this study was to determine whether anti-Jo-1 antibody levels correlate with disease activity in idiopathic inflammatory myopathy (IIM).
BACKGROUND: Although previous small case series have suggested a relationship between anti-Jo-1 antibody levels and various manifestations of IIM, larger studies are needed to establish the potential role of these levels as a biomarker for disease activity.
METHODS: Sera were collected from 81 patients with anti-Jo-1 antibodies (determined by immunodiffusion) between 1975 and 2005. Anti-Jo-1 antibody levels were quantified using a commercially available ELISA kit, and corresponding clinical data regarding disease activity was retrospectively abstracted via chart review. Disease activity was graded (without knowledge of the antibody levels) using the Myositis Disease Activity Assessment Tool (MDAAT) which is designed to capture the physician’s assessment of disease activity in 7 different organ systems (constitutional, skin, articular, gastrointestinal, pulmonary, cardiovascular, and muscle) via the MITAX and MYOACT tools. Statistical analysis utilized Spearman correlation coefficients to assess cross-sectional associations between antibody levels and organ system-specific disease activity, while multiple regression analysis was used to investigate the relationship between anti-Jo-1 antibody levels and disease activity in patients with multiple serum samples.
RESULTS: Cross-sectional assessment of 81 patients possessing anti-Jo-1 antibodies revealed a modest correlation between anti-Jo-1 antibody level and serum creatine kinase (CK) as well as muscle and joint disease activity: CK (R=0.38, p=0.001); muscle MYOACT (R=0.37, p=0.001); skeletal MYOACT (R= 0.36, p=0.001).
There were no significant correlations between the antibody level and constitutional, skin, gastrointestinal, pulmonary, or cardiovascular disease activity.
In nine patients with serial samples, the antibody levels correlated significantly with CK, muscle, joint, and pulmonary disease activity. After accounting for interpatient variability, the adjusted R2 was 0.53 for CK (p=0.001), 0.60 for muscle myoact (p=0.001), 0.53 for joint myoact (p=0.001), and 0.67 for lung myoact (p<0.0001). Global disease activity also showed a significant correlation with anti-Jo-1 antibody levels (MITAX adjusted R2=0.66, p=0.001; MYOACT adjusted R2= 0.65, p<0.0001).
CONCLUSIONS: In this large series of patients with IIM, anti-Jo-1 antibody levels correlated modestly with muscle and joint disease. More provocative correlations emerged in a smaller longitudinal subset of patients.
COMMENT : These authors appropriately suggest that monitoring anti-Jo-1 antibody levels may be useful in following the course of disease activity in patients with IIM, though a prospective analysis is necessary to confirm this finding. This is a unique study which has some parallel to the concept of following ANCA titers in systemic vasculitis as a surrogate for disease activity. If antibody titers are indeed correlative with disease activity, this suggests a possible pathogenic role of the antisynthetase autoantibodies – a subject of considerable debate.