To assess the incidence of venous thromboembolic events (VTEs) in patients with idiopathic inflammatory myopathies (IIMs), to compare the incidence of VTEs in IIM to the incidence in the general population, and to identify patient categories at high risk and investigate the development of risk in relation to a diagnosis of IIM.
Using nationwide registers, we identified a cohort of 440 individuals with newly diagnosed IIM and 4,459 individuals from the general population. Patients with IIM were diagnosed between 2005 and 2011. The start of follow-up was the date of IIM diagnosis and the corresponding date in the general population. VTE was defined as hospital care with an International Statistical Classification of Diseases and Related Health Problems, Tenth Revision code indicating VTE, with a filled prescription for anticoagulant medication. Incidence rates including 95% confidence intervals (95% CIs) were calculated, and Cox proportional hazards models were used to compare the risk of VTE in patients with IIM to the risk in the general population.
The incidence of VTEs was higher in patients with IIM than in the general population and was highest in patients who previously had cancer, who were ages >71 years when diagnosed with IIM, or who had dermatomyositis. The overall hazard ratio (HR) of VTE comparing the IIM cohort to the general population was 7.81 (95% CI 4.74, 12.85). The HR was highest the first year after IIM diagnosis, with HR 26.6 (95% CI 10.4, 68.0).
Patients with IIM are at increased risk of VTE compared to the general population, especially during the first year after the diagnosis. Preventive measures should be focused on patients who previously have had cancer, who are ages >71 years when diagnosed, or who have dermatomyositis.