FORCED VITAL CAPACITY IN PATIENTS WITH SYSTEMIC SCLEROSIS ASSOCIATED PULMONARY FIBROSIS: PREDICTORS OF MEANINGFUL DECLINE

Abstract Background Pulmonary fibrosis (PF) is common in systemic sclerosis (SSc) and serial pulmonary function tests (PFTs) are used for routine PF monitoring. Forced vital capacity (FVC) decline reflects progression in PF and FVC is frequently used as an endpoint in clinical trials. We explore the changes in FVC over time in patients with SSc-PF, receiving standard management, including immunosuppression. Methods Only SSc patients with CT-confirmed PF were included. FVC changes over the first 10 years from onset and their associations were assessed using linear mixed effects models. Predictors of time from first PFT to development of threshold FVC (FVC<70% and FVC<50%) were analysed using Cox regression. Results We identified 505 SSc-PF subjects, 21.6% were male, average age at onset was 47 years and 49.3% had diffuse cutaneous subset (dcSSc). The most common autoantibody was anti-Scl70 in 40.4%, followed by anti-RNA polymerase (ARA) in 11.7% and anti-centromere (ACA) in 7.1%. In 16.4% of the patients, ANA was positive, but no ENAs were identified (ANA+ENA-). Average FVC at 12 months from onset was 80.1% (SD 19.3) and this declined by 0.32% per year (p = 0.007) at a group level. There was no significant correlation between baseline FVC and subsequent change (correlation coefficient -0.13; 95%CI -0.26, 0.01). For every year older age at onset, average FVC increased by 0.32%, p < 0.001. Males had 3.3% lower FVC at 1 year from onset (p < 0.001) and 0.6% faster decline per year (p = 0.034) compared to females. DcSSc subjects had 5.6% lower FVC compared to limited disease (p = 0.003). Average FVC at 1 year from onset in ARA+ subjects were higher than any other antibody (15.1% v. ANA+ENA-, p < 0.001; 14.6% v. ATA, p < 0.001 and 12.5% v. ACA, p = 0.010). Nevertheless, ARA+ subjects had FVC decline rates similar to ATA+ and ANA+ENA- subjects, while ACA+ patients had a small but significant increase in FVC over time. Factors that increased the risk for FVC drop below the thresholds were male sex, ATA and low baseline FVC (Table 1). Conclusion This study provides insight into long-term patterns of FVC change and develops a model that may help predict those most at risk of significant decline. Disclosures S.I. Nihtyanova None. E.C. Derrett-Smith None. C. Fonseca None. V.H. Ong None. C.P. Denton None.