Multiple Breath Washout in Primary Ciliary Dyskinesia: Potential for Lung Disease Monitoring

Primary ciliary dyskinesia (PCD) is a heterogeneous genetic disorder characterized by structural and functional abnormalities of motile cilia, leading to chronic oto-sino-pulmonary symptoms and progressive lung damage. Markers of early lung disease in PCD may help to identify individuals who may benefit from closer monitoring or earlier, more aggressive interventions. Multiple Breath Washout (MBW) offers a noninvasive assessment of ventilation distribution inhomogeneity. Whether MBW could serve as a marker of early lung disease in PCD or could be used as an efficacy endpoint in clinical trials in PCD remains to be established. This narrative review evaluates current literature on the role of MBW in early detection and tracking of PCD-related lung disease progression, focusing on its sensitivity compared to spirometry and to the results obtained in different PCD genotypes and phenotypes. Current evidence suggests that LCI outperforms spirometry in detecting early lung abnormalities, but it may also be overly sensitive in this population. The role of LCI in long-term disease monitoring remains uncertain, requiring more robust longitudinal data. Alternative MBW indices, such as S cond and S acin , might offer additional insights into the source of ventilation heterogeneity along the respiratory tract but need further validation. The correlation of MBW with imaging modalities, though inconsistent, underscores the potential value of LCI as a non-invasive marker for tracking PCD lung disease, supporting further research to confirm its clinical utility in PCD management.