β-thalassemia Major: Thin-Section CT Features and Correlation with Pulmonary Function and Iron Overload

Abstract

PURPOSE: To describe and quantify thin-section computed tomographic (CT) features of the lung in patients with β-thalassemia major (β-TM) and determine the correlation between thin-section CT findings, pulmonary function test (PFT) results, and iron overload. MATERIALS AND METHODS: Forty-one patients with β-TM (mean age, 24.5 years) underwent thin-section CT (during full inspiration and expiration) and PFTs. Two radiologists in consensus recorded the presence of focal bronchial and parenchymal abnormalities and air trapping. A semiquantitative air trapping score (ATS) was used, and patients were separated into air trapping-negative (ATS between 0 and 3) and air trapping-positive (ATS > 3) groups for statistical analysis. Iron overload was estimated by calculating the ratio of the signal intensity (SI) of the liver to the SI of paraspinous muscle by using magnetic resonance imaging in 27 patients (66%). We performed multiple logistic regression analysis to study the influence of age, PFT findings, and SI ratio on the presence of air trapping at CT and multivariate regression analysis to study the simultaneous influence of the presence of air trapping on obstructive PFT indexes. RESULTS: Air trapping was the predominant thin-section CT finding and was seen in 10 (24%) of 41 patients. No patient had interstitial lung disease at CT, although 11 (27%) had a restrictive spirometric pattern. Simple logistic regression analysis revealed significant associations between ATS and forced expiratory volume in the first second (FEV1), FEV1/forced vital capacity (FVC), forced expiratory flow (FEF) in the midexpiratory phase (FEF25%-75%), FEF at 50% of the FVC (FEF50%), and FEF at 75% of the FVC (FEF75%) (P = .019, .030, .007, .034, and .021, respectively) but not between ATS and SI ratio. At multiple logistic regression analysis, only FEF25%-75% was significantly associated with ATS (P = .019, adjusted odds ratio = 0.86, R2 = 41.8%). Multivariate analysis revealed that ATS did not have a significant influence on lung function indexes (P = .104), although significant effects were found with FEV1, FEF25%-75%, FEF50%, and FEF75% when examined separately. CONCLUSION: Air trapping may be present at expiratory thin-section CT in patients with β-TM and is associated with reduced FEF 25%-75% values but not hepatic iron overload. © RSNA, 2003.