Asthma-COPD Overlap Linked to Occupational Pollutants

Jeff Craven

March 09, 2021

The development and worsening of overlapping asthma and chronic obstructive pulmonary disease (COPD) can be affected by pollutants found in rural and urban environments, according to a recent presentation at the annual meeting of the American Academy of Allergy, Asthma, and Immunology, held virtually this year.

"Urban-rural-occupational air pollutants or respiratory sensitizers impact asthma and the asthma-COPD overlap features," Jill A. Poole, MD, division chief of allergy and immunology at the University of Nebraska Medical Center, Omaha, said in her presentation.

The Global Initiative for Asthma (GINA) first outlined a syndrome in 2015 described as "persistent airflow limitation with several features usually associated with asthma and several features usually associated with COPD" and called asthma-COPD overlap syndrome. In 2017, a joint American Thoracic Society/National Heart, Lung, and Blood Institute workshop outlined knowledge gaps about asthma-COPD overlap, noting it "does not represent a single discrete disease entity."

"This is not a single disease and should be thought of as being heterogeneous and used as a descriptive label for patients commonly seen in clinical practice," Poole said. "Both asthma and COPD definitions are not mutually exclusive because each disease includes several phenotypes with different underlining mechanisms." An example of how asthma-COPD overlap might present is through a patient with allergic asthma who has a history of smoking who develops airflow obstruction that isn't fully reversible, or a patient with COPD "with high reversible airflow, obstruction, type 2 inflammation, and perhaps the presence of peripheral blood eosinophils or sputum eosinophils."

A patient's interaction with urban, rural, and occupational environments may additionally impact their disease, Poole explained. "The environmental factors of an urban versus rural environment may not be necessarily mutually exclusive," she said. "It's also important to recognize occupational exposures that can be both seen in an urban or rural environment [can] contribute to asthma-COPD overlap."

In a study of 6,040 men and women with asthma living in Canada, 630 (10.4%) had asthma-COPD overlap, with increased air pollution raising the likelihood of developing asthma-COPD overlap (odds ratio, 2.78; 95% confidence interval, 1.62-4.78). These people experienced later onset asthma, increased emergency department visits before a diagnosis of COPD, and increased mortality. Another study in Canada of women from Ontario in the Breast Cancer Screening Study found 1,705 of 4,051 women with asthma also had COPD. While air pollution did not increase the risk of developing asthma-COPD overlap, there was an association between body mass index, low level of education, living in a rural area, and smoking status.

Among farmers in rural areas, "it has been recognized that there is something called the asthma-like syndrome that's been reported in adult farming communities," Poole said, which includes "some degree of airflow obstruction and reversibility" that can be worsened by smoking and could be an overlap of asthma and COPD. Farmers can also experience asthma exacerbations while working, and "livestock farmers appear more at risk of developing [chronic bronchitis and/or COPD] than do the crop farmers," she noted.

Occupational environments outside of agriculture exposure can cause incident asthma, with high-molecular-weight antigens such as flour cereal, animal dander, latex, psyllium, crab processing products, and enzymes as well as low-molecular-weight antigens such as isocyanates, woods, antibiotics, glues, epoxies colophony products, and dyes presenting a risk. In food processing, main allergen sources can include raw and processed animal and plant products, additives and preservatives, contaminants from microbes or insects, inhaled dust particles or aerosols, which can be "IgE mediated, mixed IgE-mediated and non-lgE mediated."

While some studies have been conducted on the prevalence of work-related asthma and asthma-COPD overlap, "in general, the prevalence and clinical features have been scarcely investigated," Poole said. One survey of 23,137 patients found 52.9% of adults with work-related asthma also had COPD, compared with 25.6% of participants whose asthma was not work related.

To prevent asthma-COPD overlap, Poole recommended tobacco cessation, reducing indoor biomass fuel use, medical surveillance programs such as preplacement questionnaires, and considering "reducing exposure to the respiratory sensitizers with ideally monitoring the levels to keep the levels below the permissible limits."

Poole noted there is currently no unique treatment for asthma-COPD overlap, but it is "important to fully characterize and phenotype your individual patients, looking for eosinophilia or seeing if they have more neutrophil features and whether or not the allergy features are prevalent and can be treated," she said. "[A]wareness is really required such that counseling is encouraged for prevention and or interventional strategies as we move forward."

For patients with features of both asthma and COPD where there is a high likelihood of asthma, treat the disease as if it were asthma, Poole said, but clinicians should follow GINA GOLD COPD treatment recommendations, adding on long-acting beta-agonists (LABAs) and long-acting muscarinic antagonists (LAMAs) when needed, but avoiding LABAs and/or LAMAs without use of inhaled corticosteroids, and avoiding oral corticosteroids entirely. Clinicians should be reviewing the treatments of patients with asthma and COPD features "every 2-3 months to see how their response is to it, and what additional therapies could be used," she said.

Poole reports receiving grant support from National Institute of Environmental Health Sciences, National Institute for Occupational Safety and Health, and the Central States Center for Agricultural Safety and Health at the University of Nebraska Medical Center.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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