Validation of a Dyspnea Visual Analogue Scale in Fibrotic Interstitial Lung Disease
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RATIONALE: A visual analogue scale (VAS) is a simple and easily administered tool for measuring impact of disease; however, little is known about the use of a Dyspnea VAS in interstitial lung disease (ILD). OBJECTIVE: To validate the use of a Dyspnea VAS in a large and heterogenous cohort of patients with fibrotic ILD, including its minimal clinically important difference (MCID), responsiveness to change, and prognostic significance. METHODS: Patients with fibrotic ILD were identified from a large prospective registry. Validity of a 100mm Dyspnea VAS was assessed by testing its correlation in change score with other measures of ILD severity, including the University of California San Diego Shortness of Breath Questionnaire (UCSDSOBQ), King's Brief Interstitial Lung Disease quality of life questionnaire Breathlessness and Activities Domain (KBILD-B), European Quality of Life visual analogue scale (EQ-VAS), forced vital capacity (FVC), and diffusion capacity of the lung for carbon monoxide (DLCO). Responsiveness of the Dyspnea VAS was qualitatively confirmed based on there being an observable difference in the change in Dyspnea VAS across tertiles of change in anchor variables. The minimum clinically important difference (MCID) in Dyspnea VAS was calculated using both anchor (linear regression) and distribution (one-half standard deviation) approaches, with anchors including the above variables that had a correlation with Dyspnea VAS (|r|0.30). The association of Dyspnea VAS with time to death or transplant was determined. RESULTS: The cohort included 826 patients with fibrotic ILD, including 127 patients with follow-up measurements at 6 months. Mean baseline Dyspnea VAS was 5324mm. Dyspnea VAS change scores were moderately correlated with UCSDSOBQ (|r|=0.55) and KBILD-B (|r|=0.44), and weakly correlated with EQ-VAS (|r|=0.19), FVC% (|r|=0.21) and DLCO% (|r|=0.05). MCID was 2.7 to 4.5 using the more reliable anchor-based methods and 12.0 based on distribution-based methods. Dyspnea VAS was associated with time to death or transplant in unadjusted models and after adjustment for age and sex (hazard ratio 1.16 and 1.15 respectively, p<0.05 for both). CONCLUSION: This study provides support for the use of Dyspnea VAS in patients with fibrotic ILD, with an estimated anchor-based MCID of 5mm.
