From the Guidelines
Small airway disease on a chest X-ray (CXR) refers to pathological changes affecting the bronchioles, which are airways less than 2mm in diameter, and may appear as areas of increased lung markings, hyperinflation, or a reticular pattern, though these findings can be subtle and easily missed. On a CXR, small airway disease can result from various conditions including asthma, chronic bronchitis, bronchiolitis, respiratory bronchiolitis, and early stages of chronic obstructive pulmonary disease (COPD) 1. Because the bronchioles are so small, CXR has limited sensitivity for detecting small airway disease, and high-resolution CT scanning is often needed for definitive diagnosis 1.
Key Considerations
- Small airway disease can be difficult to identify and may result from a variety of causes, requiring a high index of suspicion and a complete evaluation 1.
- A comprehensive medical history, physical examination, physiologic testing, and radiographic studies are necessary for diagnosis 1.
- HRCT scanning is limited to airways that are > 2 mm in diameter, and normal bronchioles cannot be visualized, making it essential to consider indirect features such as air-trapping or subsegmental atelectasis 1.
Diagnostic Approach
- A high-resolution CT scan with expiratory cuts is often necessary to diagnose small airway disease, as CXR findings can be normal or subtle.
- Direct signs of abnormal bronchioles on HRCT include dilation or airway wall thickening, nodular branching, and linear branching “tree-in-bud” abnormalities 1.
- Indirect features such as mosaic attenuation on expiratory scanning and subsegmental atelectasis can also indicate small airway disease 1.
Treatment and Management
- Treatment depends on the underlying cause but often includes bronchodilators, inhaled corticosteroids, and sometimes systemic steroids for acute exacerbations.
- Smoking cessation is crucial for those who smoke, as continued smoking can worsen small airway damage and accelerate disease progression.
From the Research
Definition of Small Airway Disease
Small airway disease refers to the pathological changes that occur in the small airways of the lungs, which can lead to airflow limitation and defective alveolar ventilation 2. The small airways are defined as those with a diameter of less than 2mm, and are the major site of airway inflammation and obstruction in chronic obstructive pulmonary disease (COPD) 3.
Characteristics of Small Airway Disease
Small airway disease is characterized by inflammation, damage, tissue remodelling, and eventually airway loss, which can lead to airflow limitation and defective alveolar ventilation 2. The disease can be detected using various techniques, including impulse oscillometry, lung imaging methods, and spirometry 3, 2, 4.
Diagnosis of Small Airway Disease
There is no gold standard for detecting small airway dysfunction, but techniques such as spirometry, body plethysmography, and high-resolution CT can provide information on air trapping and pulmonary emphysema 3. Impulse oscillometry, gas washout techniques, and analysis of exhaled nitric oxide are also diagnostic tools that can be used to detect small airway disease 3, 4.
Key Features of Small Airway Disease
The key features of small airway disease include:
- Inflammation and obstruction of the small airways
- Airflow limitation and defective alveolar ventilation
- Tissue remodelling and airway loss
- Small airway dysfunction can occur prior to any overt airway obstruction being detectable by conventional spirometry techniques 5
- The disease can be detected using various techniques, including impulse oscillometry, lung imaging methods, and spirometry 3, 2, 4
Importance of Small Airway Disease
Small airway disease is an important feature of COPD and asthma, and can contribute to symptoms and disease progression 5. Targeting small airways early in the course of COPD may help to slow disease progression and reverse damage 2. However, there are significant gaps in our understanding of small airway disease, and further research is needed to develop novel therapies that can directly combat early airways disease processes 5.