Asthma and Chronic Obstructive Pulmonary Disease: Similarities and Differences

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Key points

  • Asthma in childhood and chronic obstructive pulmonary disease (COPD) in smokers are easily distinguishable disease entities.

  • There exist overlap phenotypes of asthma and COPD, such as asthma with neutrophilia and/or without bronchodilator response, and COPD with eosinophilia and/or some bronchodilator response.

  • Differences in physiology, symptoms, inflammation, and remodeling between asthma and COPD are obscured by smoking. Hence asthma in a smoker and COPD appear similar (ie, they show

Definitions

Asthma is currently defined as a chronic inflammatory disorder of the airways in which many cells and cellular elements play a role. The chronic inflammation is associated with airway hyperresponsiveness that leads to recurrent episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night or in the early morning. These episodes are usually associated with widespread, but variable, airflow obstruction within the lung that is often reversible either spontaneously or

Symptoms

It is difficult to differentiate asthma and COPD based on respiratory symptoms.16 In the extremes with a sudden attack of wheeze and dyspnea after allergen exposure, it is clear that this is compatible with asthma. However, in the chronic forms, symptoms are many times more diffuse and patients with asthma may have symptoms of chronic cough and/or sputum production17, 18 formerly thought to imply COPD, especially when irreversible airway obstruction has developed.19 In contrast, patients with

Genetics and environment

Genetic factors contribute to the development of both asthma and COPD, in conjunction with environmental factors. Many environmental factors contribute to both asthma and COPD and some only to either asthma or COPD alone. Table 2 shows an overview of these factors as published in a recent review.65 More severe airway hyperresponsiveness, lower lung function, maternal smoking during pregnancy, air pollution, and personal cigarette smoking are risk factors for development of both asthma and COPD.

Inflammation and remodeling

Inflammation and remodeling are present in COPD throughout the bronchial tree and lung tissue. There are 3 distinct processes present, and in different combinations in COPD: (1) chronic sputum production and cough, so called chronic bronchitis; (2) small airway disease; and (3) emphysema, which is the loss of elastic tissue in the peripheral lung.70 Respiratory bronchioles of young smokers are already inflamed,70 likely reflecting early signs of COPD. This inflammation has been shown to

Pharmacologic responses

One of the difficulties in discussing treatment response in asthma and COPD is that patients with overlap phenotypes of asthma and COPD have been systematically excluded from drug trials, which are designed to include patients with pure COPD and pure asthma. This exclusion represents a problem for evidence-based guidelines on obstructive airway disease. Travers and colleagues89 showed that only 5 of 100 individuals identified with COPD in a general population survey would fulfill inclusion

Summary

It is easy to differentiate pure asthma from pure COPD, because they reflect the extremes of a spectrum. However, in many, especially older, patients, features of both asthma and COPD can be present, leading to an overlap phenotype. There is no extensive literature available on the overlap phenotype, and interpretation of studies thus far has been hampered by differential age and smoking status in asthma and COPD. The balance of evidence so far suggests that the severity of airway obstruction

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