Elevated eosinophil levels and interleukin-4 (IL-4) levels were significantly associated with an increased risk of overlapping asthma and chronic obstructive pulmonary disease (COPD) in firefighters exposed to toxins at the World Trade Center on Sept. 11, 2001.
Patients with asthma/COPD overlap experience decreased quality of life and increased mortality, compared with patients who have either isolated COPD or isolated asthma, and longitudinal data on risk factors for the overlapping condition are lacking, wrote Ankura Singh, MPH, of Albert Einstein College of Medicine, New York, and colleagues.
In a study published inthe researchers reviewed data from 2,137 firefighters exposed to toxins at the World Trade Center on 9/11. The study participants underwent a bronchodilator pulmonary function test between Sept. 9, 2001, and Sept. 10, 2017, and at least three routine monitoring pulmonary function tests between these two dates.
In a multivariate analysis, eosinophil concentration of at least 300 cells/mcL was a significant predictor of asthma/COPD overlap. Serum IL-4 levels also were significant predictors of asthma/COPD overlap (hazard ratio, 1.51).
In addition, a greater concentration of IL-21 was associated with both isolated asthma and isolated COPD, but not with the overlap.
The study results were strengthened by the availability of pre-exposure medical data for the firefighters and the close follow-up, although limitations included the mostly white male population and a limited definition of asthma, the researchers noted.
However, the findings suggest that “high eosinophil concentrations, uniquely associated with asthma/COPD overlap in this population, may reflect biological pathways that predispose one to exaggerated inflammation and/or poor counterregulatory responses to inflammation, leading to reversible and fixed airflow obstruction,” they wrote. Consequently, early interventions targeting specific inflammatory pathways may improve lung function outcomes.
The study was supported in part by the National Institute of Occupational Safety and Health and the National Institutes of Health.
SOURCE: Singh A et al. CHEST. 2018 Dec;154;1301-10.