Clearly there were differences between the Irish and Swedish cohorts in longitudinal progression, with the annual change in CT score equal to + 1.6% and FEV1 equal to — 0.4%, compared to – 2.7% and -2.3% in the Irish cohort, respectively. For individual HRCT abnormalities, de Jong et al found no change in mucus plugging over time in their adult patients in contrast to our results in which mucus plugging worsened predominantly in the group with mildly impaired lung function. Such discrepancies may be related to differences in treatment or in patient populations. Some European centers have followed a more aggressive policy of early antibiotic intervention from time of diagnosis, which may influence decline in spirometry results over time. More info
Alternatively, the genetic makeup of our patients may differ from other populations, and it is clear that genotype strongly influences the phenotypic expression of CF lung disease. It would be extremely interesting to perform a multicenter study evaluating such differences between populations and their influence on CT and spirometric changes over time. Despite these individual abnormality differences, our overall findings corroborate those of de Jong et al and suggest that mucus plugging occurs earlier in CF lung disease and at a milder stage of lung function impairment, and that bronchiectasis may be an end sequel of such antecedent abnormalities.
Reports of the prevalence of air trapping in adults with CF are limited. The prevalence increases with progressively worsening radiologic appearances. We found air trapping deteriorated significantly faster than FEV1 over time, and this decline was most marked in the moderate-severely impaired lung function group. This finding in conjunction with the reduction in FEF25-75% suggests ongoing peripheral airways disease. CT pathology studies evaluating the association between bronchiectasis and air trapping have shown that hyperlucency on expiratory CT adjacent to bronchiectasis represents constrictive bronchiolitis histologically. Because it showed more rapid decline than FEV1 over time, air trapping may serve as a useful additional outcome measure in patients with CF. A potential obstacle is the poor-to-moderate interobserver agreement between read-ers. However, quantitative methods using spiro-metrically triggered HRCT may improve this variability, as they are more sensitive to regional changes in air trapping than spirometry alone. Additionally, in a recent, double-blind, randomized controlled trial of dornase alfa in children with CF, quantitative air trapping measurements were more sensitive to treatment-related changes in regional air trapping than spirometry or total HRCT scores alone.