What lung findings are specific to alpha 1 antitrypsin deficiency?

Specific Lung Findings in Alpha-1 Antitrypsin Deficiency

The most specific lung finding in alpha-1 antitrypsin deficiency is panacinar emphysema with predominant lower lobe distribution, which can be best visualized on high-resolution computed tomography (HRCT). 1

Radiographic Findings

Chest X-ray Findings

• Early disease: Often normal
• Advanced disease:
  • Hyperinflation and increased radiolucency of lungs, particularly in lower lung segments
  • Diaphragmatic flattening in lateral projection (most specific X-ray finding)
  • Low and flat diaphragms
  • Exaggerated verticality of the heart
  • Increased anterior-posterior diameter of the chest
  • Widening of retrosternal space
  • Decreased vascular markings, mainly in lower zones (contrasting with upper zone predominance in non-AAT emphysema)
  • Possible enlargement of hilar pulmonary arteries (suggesting pulmonary hypertension) 1

High-Resolution CT Findings

• Classic finding: Panacinar emphysema with uniform abnormally low attenuation of lobules
• Predominant lower lobe distribution (distinguishing from usual emphysema which typically affects upper lobes)
• Fewer and smaller pulmonary vessels in affected lung areas
• Potential bronchial wall thickening and/or dilation 1, 2
• Less common: bullae (more common in non-AAT emphysema) 1

Pulmonary Function Test Findings

• Obstructive pattern with:

  • Reduced FEV1 (forced expiratory volume in 1 second)
  • Normal or reduced FVC (forced vital capacity)
  • Reduced FEV1/FVC ratio
  • Flow-volume curves showing marked decrease in flow with decreasing lung volumes
  • Concavity of expiratory portion of flow curve 1

• Hyperinflation pattern:

  • Increased residual volume (RV)
  • Increased total lung capacity (TLC)
  • Static lung volumes by plethysmography greater than those measured by dilution techniques (due to air trapping) 1

• Gas exchange abnormalities:

  • Reduced diffusing capacity (DLCO)
  • Widened alveolar-arterial oxygen gradient
  • Decreased PaO2 during exercise 1

• Important caveat: Some patients with severe AAT deficiency, significant airflow obstruction, and radiographic emphysema may have repeatedly normal DLCO despite prominent panacinar emphysema on HRCT 3

Ventilation-Perfusion Scan Findings

• Symmetric distribution of xenon-133 throughout all lung zones during equilibrium phase
• Symmetric delay in washout, most prominent in lung bases and midzones
• Symmetric loss of pulmonary arterial perfusion, most marked in the bases
• May detect early changes even in individuals with relatively normal lung function 1

Bronchiectasis

• Present in approximately 40-43% of patients with AAT deficiency
• Characterized by bronchial wall thickening and/or dilation
• May be more a result of emphysematous changes in the parenchyma than of AAT deficiency itself 1

Clinical Implications

The specific pattern of lower lobe predominant panacinar emphysema on HRCT is highly suggestive of AAT deficiency and should prompt testing for the condition, especially in patients with:

• Early-onset emphysema (regardless of smoking history)
• Emphysema with minimal smoking history
• Emphysema with basilar predominance
• Unexplained liver disease
• Family history of emphysema or liver disease 1

HRCT is significantly more sensitive than chest X-ray or pulmonary function tests for detecting early emphysematous changes and should be considered the gold standard imaging modality for diagnosis and monitoring of lung disease in AAT deficiency 2, 4.

Remember that the presence of significant bronchodilator responsiveness does not rule out AAT deficiency, as many patients may demonstrate this feature and can be misdiagnosed with asthma 3.

The specific pattern of lung findings in AAT deficiency has important implications for mortality and morbidity, as early detection can lead to interventions such as smoking cessation, appropriate vaccinations, and consideration of augmentation therapy in suitable candidates 5, 6.