Etymology

• Derived from the term small airways, referring to airways less than 2 mm in diameter, and disease, indicating pathological changes.

AKA

• Bronchiolitis
• Small airway obstruction

Definition

• What is it? Small airway disease encompasses a group of conditions affecting the bronchioles (airways <2 mm in diameter), characterized by inflammation, fibrosis, or obstruction that impairs airflow.
• Caused by:
  • Inflammation: Chronic exposure to irritants (e.g., cigarette smoke, environmental pollutants).
  • Infection: Viral or bacterial bronchiolitis.
  • Autoimmune: Diseases like rheumatoid arthritis or sarcoidosis.
  • Obstruction: Airway narrowing or collapse from fibrosis or external compression.
• Resulting in:
  • Structural changes: Narrowing, obliteration, or dilation of small airways.
  • Pathophysiology: Airflow limitation due to obstruction or loss of elastic recoil.
  • Pathology: Chronic inflammation, peribronchiolar fibrosis, and mucus plugging.
• Diagnosis:
  • Clinical: Symptoms include progressive dyspnea, wheezing, cough, or exercise intolerance.
  • Radiology: Detectable on imaging, with findings such as mosaic attenuation or air trapping on expiratory CT.
  • Labs: Typically non-specific; blood tests may show markers of systemic inflammation or autoimmune activity.
• Treatment: Management includes addressing underlying causes, smoking cessation, bronchodilators, anti-inflammatory therapies, and immunosuppressants when appropriate.

Radiology

• CXR
  • Findings: May appear normal in early disease or show hyperinflation, peribronchial thickening, or areas of low density.
  • Associated Findings: Subtle findings may include small opacities or signs of air trapping.
• CT
  • Parts: Bronchioles and surrounding interstitium.
  • Size: Affects airways <2 mm in diameter.
  • Shape: Irregular or constricted bronchioles, often with thickened walls.
  • Position: Typically diffuse but can be focal in certain diseases.
  • Character: Mosaic attenuation, centrilobular nodules, and areas of air trapping on expiratory imaging.
  • Time: Chronic or progressive changes in inflammatory or fibrotic diseases.
  • Associated Findings: Bronchiectasis, mucus plugging, and hyperinflation.
• Other Imaging Modalities
  • MRI may provide functional ventilation-perfusion data in research settings.
  • Ventilation-perfusion scans can highlight ventilation defects in severe disease.

Key Points and Pearls

• Small airway disease is often subclinical in early stages and detected through imaging or pulmonary function tests (PFTs).
• PFTs typically demonstrate an obstructive pattern with decreased FEV1 and FEV1/FVC ratio.
• Mosaic attenuation on CT is a hallmark finding, particularly when paired with expiratory imaging.
• Early detection and intervention can prevent progression to advanced airflow limitation or chronic obstructive pulmonary disease (COPD).
• Smoking cessation and environmental control are critical in management.