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Background: Low-dose erythromycin therapy improves airflow limitation and airway inflammation in patients with diffuse panbronchiolitis (DPB). However, to our knowledge there has been no study to determine whether physiologic improvement during erythromycin therapy correlates with radiologic findings.Study Objective: To clarify whether improvement in pulmonary function correlates with specific changes on chest CT.Design: The relationship between five CT findings and five pulmonary function parameters was evaluated before and 3 months after low-dose erythromycin therapy in 24 patients with DPB retrospectively.Results: After erythromycin therapy, the predicted percentage of vital capacity (%VC; 87.0 +/- 3.07% vs 98.9 +/- 3.39%; p = 0.00006) and 50% of the maximum midexpiratory flow rate of FVC (1.41 +/- 0.26 L/s vs 1.61 +/- 0.27 L/s; p = 0.03) significantly increased, and the residual volume/total lung capacity ratio (RV/TLC%; 44.5 +/- 1.93% vs 40.7 +/- 1.83%; p = 0.0019) significantly decreased, but the FEV(1) to FVC ratio and 25% of the maximum expiratory flow rate of FVC did not. In five CT findings, centrilobular nodules (3.7 +/- 0.4 vs 1.5 +/- 0.3; p = 0.0001), peripheral bronchiolar wall thickness (3.8 +/- 0.3 vs 2.6 +/- 0.4; p = 0.0007), and peripheral bronchiolectasis (2.8 +/- 0.3 vs 2.2 +/- 0.4; p = 0.0058) had significantly improved, whereas low attenuation area and central bronchiectasis had not. There were positive correlations of improved scores of centrilobular nodules with improved %VC (r = 0.58, p = 0.0062) and RV/TLC% (r = 0.64, p = 0.0022).Conclusions: Decreased air trapping in DPB correlates with an improvement of centrilobular nodules, which reflects the obstructive lesions of bronchioles during the erythromycin therapy. [ABSTRACT FROM AUTHOR]