Main differentiating and overlapping features of asthma and COPD
| Feature | Asthma | COPD | Exceptions and overlapping features |
|---|---|---|---|
| Risk factors | Allergens | Smoking | Smoking may be an aggravating factor in asthma; children with early-life wheezing have a higher risk of developing asthma as teenagers and chronic obstructive pulmonary disease (COPD) as adults (the “Dutch hypothesis”); repeated airway infections may trigger development of either asthma or COPD, depending on the nature of infection and the intrinsic genetic predisposition (the “British hypothesis”) |
| Anatomic segment involved | Airways | Airways and parenchyma | Severe asthma exacerbations may lead to adjacent parenchymal destruction, severe hyperinflation, and loss of scaffolding, or to radial or axial traction, or both, on the small airways |
| Atopy | Yes | No | Atopy may be present in some patients with COPD |
| Airway inflammation | Yes | Yes | Absent in mild asthma between exacerbations |
| Peripheral eosinophilia | Yes | No | Some patients with COPD may have eosinophilia; some patients with asthma may have neutrophilic infiltration (eg, severe asthma, asthma coexistent with gastroesophageal reflux and chronic rhinitis) |
| Airway eosinophilia | Yes | No | 20%–40% of patients with COPD have airway eosinophilia (if one excludes eosinophilic bronchitis, up to 20% patients with COPD can still have some eosinophilic airway infiltration) |
| Exhaled gas (lower-airway) nitric oxide concentration | High | Low | May be reduced in some asthma phenotypes, eg, neutrophilic or paucigranulocytic; may be present in some patients with COPD |
| Diffusing lung capacity for carbon monoxide | Normal | Reduced (in emphysema) | Normal in chronic bronchitis; increased in acute asthma |
| Airway resistance | High | High | Normal in mild asthma between exacerbations; normal or slightly increased in emphysema |
| Airway hyperresponsiveness | Yes | No | May be present in COPD |
| Elastic recoil of the airways and parenchyma | Normal | Reduced (in emphysema) | Reduced in acute exacerbations of severe asthma; normal in chronic bronchitis |
| Symptoms | Episodic | Persistent | May be episodic in some patients with COPD, especially during significant environmental exposures |
| Comorbidities | Atopic dermatitis, allergic rhinitis | Cardiovascular disease | Obstructive sleep apnea may complicate both conditions |