Lung function is associated with minimal EQ-5D changes over time in patients with systemic sclerosis

In systemic sclerosis (SSc) therapeutic efforts are often directed to prevent progressive respiratory impairment, but it is unclear to what extent changes in pulmonary function tests (PFTs) are associated with health-related quality of life (HRQoL). The aim of our study is to evaluate how modifications in PFTs contribute to longitudinal variations in HRQoL, assessed through the multidimensional questionnaire EQ-5D, in patients with SSc. We included SSc patients with forced vital capacity (FVC%), diffusing capacity of the lungs for carbon monoxide (DLCO%) and EQ-5D assessed in at least two visits. The EQ-5D consists of two parts, a utility score ranging from - 0.59 to 1, and a 0-100 Visual Analogue Scale (VAS). Higher values represent better health. The association between changes in FVC% and DLCO%, and evolution of EQ-5D over time, was investigated using generalized estimating equations. Three hundred seventy-eight patients were included, accounting for a total of 1619 measurements. The models showed that improvement in FVC% is significantly associated with increase in both utility score (beta = 0.001; 95% CI 0.000 to 0.002; p = 0.003) and VAS over time (beta = 0.188; 95% CI 0.111 to 0.264; p < 0.001). Moreover, improvement in DLCO% is longitudinally associated with increase in utility score (beta = 0.001; 95% CI 0.000 to 0.002; p = 0.038), while the results for VAS were non-significant (beta = 0.020; 95% CI -0.079 to 0.120; p = 0.690). We show that change in PFTs has a significant, although minor, impact on HRQoL as measured by EQ-5D in SSc.