A Longitudinal Analysis of Respiratory Symptoms in People with Cystic Fibrosis with Advanced Lung Disease on and off ETI

People with CF (PwCF), particularly those with advanced lung disease (ALD), experience frequent respiratory symptoms. A major CF breakthrough was the approval of elexacaftor/tezacaftor/ivacaftor (ETI) in 2019, which has been shown to improve symptoms and lung function in the CF population, and decrease pulmonary exacerbations. The purpose of this study was to analyze longitudinal changes in respiratory symptoms over 24 months in ETI-treated and untreated PwCF with ALD Symptoms were measured among CF adults with ppFEV < 40% (N = 48, 24 ETI-treated, 24 untreated) using the CFRSD-CRISS and the CFQ-R [respiratory]. Two multilevel growth models assessed the rate of change in symptoms overall and within the ETI-treated and untreated groups. PwCF on ETI had significantly lower symptom severity over 24 months than those not on ETI as measured by the CRISS and CFQ-R. The ETI-treated group maintained an -11.7 and +19.3 point difference(p<0.01) in CRISS and CFQ-R scores over the study compared to the non-ETI group, achieving minimal clinically important differences on average between groups on both instruments. No change in the symptom burden trajectory between groups was observed (p = 0.58). Even with ALD, ETI-treated PwCF have a lower respiratory burden than those not on ETI. This may be confounded by survivorship bias in the non-ETI group. Of note, in this ALD cohort, neither instrument demonstrated ceiling effects. Our results suggest that, while ETI has significantly improved the lived experience, PwCF with ALD are still plagued by respiratory symptoms.