To the Editor:
We read with interest the article by Chung [1] about the risk of pulmonary thromboembolism in asthmatic patients. This nationwide population cohort study suggests that the risk of developing pulmonary thromboembolism significantly is increased in asthmatic patients compared to those of the general population, with a multivariable-adjusted hazard ratio of 3.24 (95% CI 1.74–6.01). The authors considered that as concentrations of thrombin were elevated in the sputum and bronchoalveolar lavage of asthmatic patients, and as local coagulation activation existed in asthma, it is possible that the results of this study may, in part, be explained through this mechanism. However, there are other plausible mechanisms that might explain the risk.
In asthmatic patients, plasma oxidant–antioxidant status was abnormal, with increased plasma malondialdehyde and decreased plasma ascorbic acid, which support the emerging concept of free-radical injury in asthma [2]. The pathogenesis of venous thromboembolism is also linked to oxidative stress [3]. Therefore, the involvement of oxidative stress may potentiate the increased risk of pulmonary thromboembolism in asthmatic patients.
Moreover, as the study by Majoor et al. [4] suggested, on one hand, that inactivity of severe asthmatic patients might be a potential trigger for venous thromboembolic events, but on the other hand, asthmatic patients, especially severe cases, continuously use high doses of glucocorticoids, receive bursts of systemic glucocorticoid during exacerbations and often need chronic oral glucocorticoid treatment for control of their asthma. Recent studies suggested that use of glucocorticoids may be at an increased risk of venous thromboembolism [5] and pulmonary embolism [6]. Just as Chung et al. [1] recognised when discussing the limitations of their study, glucocorticoid use information was lacking in the multivariable Cox proportional-hazards regression analysis.
Notably, Majoor et al. [4] found that the risk of pulmonary embolism was increased in severe asthma only, not in mild-to-moderate asthma.
Footnotes
Conflict of interest: None declared.
- Received September 8, 2013.
- Accepted September 29, 2013.
- ©ERS 2014
