Fitness and lung function in children with primary ciliary dyskinesia and cystic fibrosis

Background: Peak oxygen uptake (VO_2peak) is associated with morbidity and mortality in health and disease, and provides important information of global physical health not achieved from standard pulmonary function tests. Primary ciliary dyskinesia (PCD) and cystic fibrosis (CF) are genetically determined diseases involving different basic defects, but both showing impaired mucociliary clearance leading to chronic infections and pulmonary destruction early in life. PCD is generally considered a milder disease than CF and it is hypothesized that children with CF would have consistently lower VO_2peak and pulmonary function than children with PCD.

Methods: We performed a prospective, observational single-center, clinical cohort study of VO_2peak and pulmonary function in age and gender matched schoolchildren, at two occasions 12 months apart.

Results: VO_2peak was persistently (at baseline and after 12 months) and significantly reduced in the 22 patients with PCD (z-score = -0.89 and -1.0) and 24 with CF (z-score = -0.94 and -1.1), included in the study. Abnormal VO_2peak was detected in a larger proportion of children with PCD (≈30%) than CF (≈13%). Moreover, children with PCD exhibited persistently lower FEV₁ (p < 0.0001 at first visit and p = 0.001 at second visit) while FEF_25-75 and FVC differed only at baseline. Indeed, a retrospective analysis comparing lung function over the last year in our entire PCD and CF populations between 6 and 18 years of age, revealed lower values in patients with PCD (FEV₁ z-score, p = 0.0004, FVC z-score p < 0.0001, FEF_25-75 z-score p = 0.008).

Conclusion: This is the first report indicating that cardiopulmonary fitness is equally and consistently reduced in both children with PCD and CF along with a consistent lower pulmonary function in PCD compared with CF. A certain reservation for possible selection bias and the small number of patients is necessary. However, increased focus on early diagnosis, evidence-based treatment regimens and close clinical monitoring in PCD are warranted.