Quantitative assessment of emphysema distribution in smokers and patients with alpha1-antitrypsin deficiency

INTRODUCTION: Identification of upper lobe emphysema is mandatory before lung volume reduction surgery (LVRS). Here we introduce a CT-based objective model for describing the distribution of different types of emphysema. METHODS: Fifty COPD patients were included in the study. Half had alpha1-antitrypsin deficiency (alpha1-COPD) and the rest had smoking-induced emphysema (usual COPD). All patients were scanned 3 times. The relative area of emphysema in each CT slice was plotted against table position, and the cranio-caudal distribution was calculated as the slope of the regression line. RESULTS: The variation in slopes within a patient was much less than the variation in slopes between patients (P<0.0001). There was a significant difference between slopes in the alpha1-COPD and the usual COPD groups (P<0.0001). In the alpha1-COPD group, 24/25 patients had lower lobe emphysema. In the usual COPD group, 4 patients had upper lope predominance, 5 patients had heterogeneous distributions, and 16 patients had lower lobe predominance. CONCLUSIONS: The majority of patients with smoking-related emphysema have a homogeneous distribution and lower lobe predominance although not as noticeable as in alpha1-antitrypsin deficiency. An objective and quantitative method for determining the distribution of emphysema should be applied when selecting candidates for LVRS.