Predictors of thrombotic events in patients with idiopathic inflammatory myopathies.

Objectives: To identify predictors of thrombotic events in patients with idiopathic inflammatory myopathies (IIM).

Methods: We conducted a retrospective study of a large, longitudinal IIM cohort followed at a single academic centre. We used Poisson regression models to estimate incidence-rate ratios (IRR) of prospective arterial and venous thrombotic events (ATE and VTE respectively).

Results: Thrombotic events occurred in 37 out of 312 patients (12%) over a median [interquartile range (IQR)] follow up time of 6[2-11] years after IIM diagnosis. Among patients with thrombotic events, 65% had VTE, which predominantly occurred within the first 3 years of IIM diagnosis, while 41% had ATE, which predominantly occurred after 10 years from IIM diagnosis. In predictive models, disease duration less than 1 year (IRR 6.49, 95%CI 1.89-22.35) was the strongest risk factor for VTE. Prior ATE was the strongest risk factor for prospective ATE (IRR 18.78, 95%CI 10.98-32.12). Traditional cardiovascular (CV) risk factors and higher levels of myositis activity and damage were other predictors of prospective ATE. The lactonase activity of PON1 was independent of the PON1 Q192R polymorphism and enhanced prediction of ATE in patients with high CV risk. IVIG was not associated with increased thrombotic risk in a high-risk population.

Conclusions: We report the incidence and risk factors for thrombotic events in a single-centre longitudinal IIM cohort, showing early occurrence of VTE and late onset of ATE. PON1 activity was predictive of ATE in a high-risk subgroup of IIM patients.