Introduction: Early diagnosis in cystic fibrosis has been shown to improve long term outcomes; similar evidence is lacking in children with primary ciliary dyskinesia. The aim of this study was to compare long term clinical outcomes according to age of diagnosis.

Methods: This is a retrospective study of children with confirmed diagnosis of PCD followed at The Hospital for Sick Children (Toronto, Canada) between 2000-2022 . The cohort was divided into three different age groups: 1) early diagnosis group, when diagnosed<1 year of age, 2) diagnosis at ages 5-9 years, 3) diagnosis at ages 10-14 years.

Results: 93 children (40/28/25 children in groups 1/2/3 respectively) with PCD were included in the study. Laterality defect (LD) and unexplained neonatal respiratory distress (NRD) were significantly more common in group 1 compared to both group 2 (LD 63% vs 36%, NRD 80% vs 36%) and group 3 (LD 63% vs 32%, NRD 80% vs 52%). At age 8, there was no significant differences in FEV1 precent predicted or body mass index between group 1 and 2 (92.4% [9.5] vs 95.8% [17.1]). At age 14, patients in group 2 had significantly higher FEV1 values compared to group 3 (92.3% (19.6) vs 81.4% (15), p=0.048). For the following three consecutive years, (ages 15-17), although not statistically significant, a similar trend was seen with annual higher FEV1 values in group 2. At age 17,  mean FEV1 values were 93% (22.7) vs 80.7% in groups 2 and 3, respectively.

Conclusion: Late diagnosis in PCD was associated with lower lung function during the adolescent years, emphasizing the importance of earlier diagnosis in children with PCD.