Validation of the cough quality-of-life questionnaire in patients with idiopathic pulmonary fibrosis

Background: Cough is a pervasive and disabling symptom of idiopathic pulmonary fibrosis (IPF) and is an independent predictor of disease progression. The Cough Quality-of-Life Questionnaire (CQLQ) is a validated measure of cough-specific quality of life that could be used as an outcome measure in therapeutic trials for IPF. This study aimed to assess the reliability and validity of the CQLQ in individuals with IPF. Methods: The CQLQ was administered as an outcome within a previously published 27-week, placebo-controlled, crossover trial of thalidomide for cough in IPF. Participants were adults with IPF and chronic cough. A cough visual analog scale (VAS) and the St. George's Respiratory Questionnaire (SGRQ) were administered to establish concurrent validity of the CQLQ. Results: Internal consistency was high (Cronbach α > .70) for the CQLQ total and four of six subscale scores. The CQLQ total score demonstrated concurrent validity through significant correlations with scores on the cough VAS and SGRQ total and subscale scores (r range, 0.63-0.81; P<.05). The intraclass correlation coefficient for the CQLQ completed at baseline and after a therapeutic washout period at week 15 was 0.87, indicating very good test-retest reliability. Conclusions: This study supports the use of the CQLQ as a valid and reliable instrument in IPF and should be used to assess cough-specific quality of life in therapeutic trials.