Validity and Reliability of the Fatigue Severity Scale in a Real-World Interstitial Lung Disease Cohort.
Academic Article
Overview
abstract
RATIONALE: Fatigue is a common and debilitating symptom for people living with Interstitial Lung Disease (ILD). Studies on fatigue in ILD are limited, and there has been little headway made toward developing interventions targeting improvement in fatigue. A barrier to progress is a lack of knowledge around the performance characteristics of a patient-reported outcome measure to assess fatigue in patients with ILD. OBJECTIVES: To assess the validity and reliability of the fatigue severity scale (FSS) for measuring fatigue in a national cohort of patients with ILD. METHODS: FSS scores and several anchors were measured in 1,881 patients from the Pulmonary Fibrosis Foundation Patient Registry. Anchors included the Short Form 6D Health Utility (SF-6D) score and a single vitality question from the SF-6D, the University of San Diego Shortness of Breath Questionnaire (UCSD-SOBQ), forced vital capacity (FVC), diffusing capacity of the lung for carbon monoxide (DLCO), and six-minute walk distance (6MWD). Internal consistency reliability, concurrent validity, and known groups validity were assessed. Structural validity was assessed using confirmatory factor analysis (CFA). MEASUREMENTS AND MAIN RESULTS: The FSS demonstrated high internal consistency (Cronbach's alpha = 0.96). There was moderate to strong correlation between the FSS and patient reported anchors (vitality question from the SF-6D {r = 0.55}, and the UCSD SOBQ total score {r=0.70}) and weak correlations between the FSS scores and physiological measures (FVC {r = -0.24}, % predicted DLCO {r = -0.23} and 6MWD {r = -0.29}. Higher mean FSS scores, indicating greater fatigue, were observed for patients using supplemental oxygen, those prescribed steroids, and those with lower %FVC and %DLCO. The CFA results suggest that the 9 questions in the FSS reflect one dimension of fatigue. CONCLUSIONS: Fatigue is an important patient centered outcome in ILD that is poorly correlated with physiologic measures of disease severity, including lung function and walk distance. These findings further support the need for a reliable and valid measure of patient-reported fatigue in ILD. The FSS possesses acceptable performance characteristics for assessing fatigue and distinguishing different levels of fatigue among patients with ILD.
