Determining the minimal clinically important difference for the questionnaire of olfactory disorders in people with cystic fibrosis and factors associated with improvement after highly effective modulator therapy.

Introduction: Olfactory dysfunction (OD) is common among people with cystic fibrosis (PwCF). The Questionnaire of Olfactory Disorders (QOD) is a validated instrument that evaluates olfactory-specific quality-of-life. The QOD minimal clinically important difference (MCID) and factors associated with olfactory improvement after elexacaftor/tezacaftor/ivacaftor have not been determined for PwCF.

Methods: Prospective observational data were pooled from three studies that enrolled adult PwCF with chronic rhinosinusitis (CRS). QOD scores and disease characteristics were assessed. To evaluate internal consistency and calculate the QOD MCID, Cronbach's alpha and four distribution-based methods were employed. For participants who enrolled prior to elexacaftor/tezacaftor/ivacaftor, QOD scores were obtained at baseline and after elexacaftor/tezacaftor/ivacaftor initiation. Multivariable regression was used to identify factors associated with QOD improvement.

Results: Of 129 PwCF included, 65 had QOD scores before and 3-6 months after starting elexacaftor/tezacaftor/ivacaftor. Mean baseline QOD score was 6.5 ± 7.9. Mean Cronbach's alpha was ≥0.85. The MCID estimates were as follows: Cohen's effect size = 1.6, standard error of measurement = 2.5, ½ baseline standard deviation = 4.0, and minimal detectable change = 6.9. Mean MCID was 3.7. Of those with pre/post elexacaftor/tezacaftor/ivacaftor QOD scores, the mean change in QOD was -1.3 ± 5.4. After elexacaftor/tezacaftor/ivacaftor, QOD improvement surpassed the MCID in 22% of participants (14/65). Worse baseline QOD scores and nasal polyps were associated with improved QOD scores after elexacaftor/tezacaftor/ivacaftor (both p < 0.04).

Conclusion: The QOD MCID in PwCF was estimated to be 3.7. Elexacaftor/tezacaftor/ivacaftor led to qualitative but not clinically meaningful improvements in QOD score for most PwCF; PwCF with worse baseline QOD scores and nasal polyps improved in a clinically significant manner.