Tomografia computadorizada de tórax e absorciometria radiológica de dupla energia na avaliação da densidade mineral óssea em pacientes pediátricos com fibrose cística

Abstract

Background: Early bone mineral density (BMD) evaluation in cystic fibrosis (CF) patients has a positive impact on patients' quality of life. Objective: the study was designed to evaluate the concordance between thoracic computed tomography (CT) and dual-energy radiological absorption (DXA) in the evaluation of BMD in patients with CF. Secondly, to evaluate the prevalence of low BMD in these patients. Methods: This is a cross-sectional study with retrospective analysis of low dose CT scans of the thorax with an iterative reconstruction processing of the images. The indication for the scans was any clinical reason requiring CT chest to assess pulmonary changes of CF patients, aged between 8 and 18 years-old. Use of anaesthesia or sedation for the CT or DXA scanning was not needed. We included sociodemographic (age, sex) and clinical (genetic mutation, laboratory tests, lung function and nutritional status) data in the analysis. The average Hounsfield values of a region of interest calliper (ROI) positioned in the trabecular bone of 3 lower thoracic vertebrae measured the bone density on CT. We positioned the ROI avoiding focal lesions or artifacts. We compared the CT bone density with the DXA scan measurements on each patient, and we calculated the correlation between both CT and DXA measurements using Pearson's correlation coefficient. Methods: Cross-sectional study with retrospective data collection, in which CT scans of the thorax performed by clinical indications in patients with CF between the ages of 8 and 18 years were performed with low radiation dose and reconstruction iterative filter without anesthetic or sedation, for the measurement of BMD. Sociodemographic data (age, sex), clinical (genetic mutation, laboratory tests, lung function and nutritional status) were evaluated. The bone density was measured in Hounsfield Units obtained by the average region of interest measurements in the central portion of three lower thoracic vertebral bodies, avoiding areas with lesions or artifacts. The measurements of bone density by chest CT were compared with the measurements of bone density from DXA and the existence of correlation between measurements was evaluated. Pearson's correlation coefficient was calculated to evaluate the correlation between the both methods (computed tomography of the chest and bone densitometry). Results: A total of 18 children and adolescents, with mean age 16.1±3.4 years were evaluated. There was a predominance of males (66.7%), and 15 (83.3%) participants were Caucasians. Three (16.7%) patients were homozygous and nine (50%) were heterozygous for F508del. The median of BMD z-score by DXA was 0.65 (−1.60 to 0.20) and the mean of thoracic CT was 229.2±30.6 HU. Fifteen (83.3%) patients were diagnosed as normal and three (16.7%), as low BMD. A strong positive correlation was observed between BMD measured by thoracic CT and DXA (r=0.740; p<0.001). Conclusions: The present study showed a strong positive correlation between thoracic CT and lumbar DXA to evaluate bone health in children and adolescents with CF. In contrast to the literature, we observed a lower prevalence of low BMD in our cohort of patients.