Correspondence Between Lung Function and Symptom Measures from the Cystic Fibrosis Respiratory Symptom Diary-Chronic Respiratory Infection Symptom Score (CFRSD-CRISS)

Background: Pulmonary exacerbations (PEx) in cystic fibrosis (CF) patients reduce quality of life. Lung function, measured by the percent predicted forced expiratory volume in 1 s (ppFEV1), is widely used to evaluate PEx treatments. We analyzed the correspondence of ppFEV1 with 8 patient-reported symptom-based questions from the Cystic Fibrosis Respiratory Symptom Diary-Chronic Respiratory Infection Symptom Score (CFRSD-CRISS).

Methods: Data were derived from the observational Standardized Treatment of Pulmonary Exacerbations (STOP) study. CF patients who had CFRSD-CRISS and ppFEV1 measurements on ≥2 timepoints were included: 1) day of initial PEx, 2) 7 days later, and/or 3) end of PEx. We calculated age-stratified Spearman correlation coefficients and 95% confidence intervals (95% CIs) between the change in ppFEV1 and change in CFRSD-CRISS items from index to day 7 and from index to the end of PEx treatment.

Results: Lung function and symptom scores improved by the end of treatment; however, correlations between ppFEV1 and the specific CFRSD-CRISS measures were mostly weak to moderate. An exception was that among patients <18, we observed moderately strong correlations between changes in ppFEV1 and cough severity (r = -0.58 (95% CI: -0.80, -0.21)), mucus quantity (r = -0.51 (-0.77, -0.11)), and wheezing (r = -0.53 (-0.78, -0.14)) from index until end of treatment.

Conclusions: As novel treatments are developed for PEx, it is important to ensure that improvement is measured meaningfully. The generally weak associations between patient-reported symptoms and ppFEV1 that we found suggest that these measures capture different aspects of the disease and both metrics are important when evaluating new treatments.