Prospective longitudinal association between repeated multiple breath washout measurements and computed tomography scores in children with cystic fibrosis.

Background: Progression of structural lung disease (SLD) is a major risk factor for morbidity in patients with cystic fibrosis (CF). We studied changes in SLD and correlations with spirometry and nitrogen multiple breath washout (NMBW) outcomes to explore associations in contemporary evolution between structural and functional abnormalities in CF lung disease.

Methods: Spirometry-controlled chest-CTs using PRAGMA-CF for scoring extent of SLD, spirometry, and NMBW were performed at two-year intervals in school-age children with CF.

Results: Fifty-seven children aged 6-18 years were included. No significant progression in mean PRAGMA-CF scores was observed. Half of the children showed improvement in the proportion of bronchiectasis (%Bx). Lung Clearance Index (LCI) and the second moment ratio (M2) increased significantly and baseline values correlated significantly with SLD at follow-up (p ≤ 0.0002). The correlation between the change in M2 (∆M2) and the change in total SLD was R = 0.27 (p = 0.048). We found high negative predictive values (100%) for ∆M2<10% to exclude progression in SLD. For stable or improving values of LCI and M2, the predicted probability for progression in SLD was 16% and 14%, respectively (upper 95% confidence limit: 33%). Evolution in NMBW and CT outcomes was discordant in half of the children.

Conclusions: We found no progression in SLD over 2 years in school-age children with CF, in contrast to both LCI and M2, which along with discordant outcomes in half of the children underlines that NMBW and CT assess different aspects of CF lung disease. However, stable outcomes from NMBW were associated with stable structural lung disease.