Longitudinal change during follow-up of systemic sclerosis: correlation between high-resolution computed tomography and pulmonary function tests

The objective of this study was to determine the correlation between functional and radiological longitudinal change in patients with systemic sclerosis-associated interstitial lung disease (SSc-ILD), and to test the OMERACT definition of clinically meaningful progression of pulmonary function tests (PFTs) for the prediction of ILD radiological evolution. We retrospectively retrieved high-resolution computed tomography (HRCT) studies and PFTs including DLco, both available at two time-points and performed within 6 months of each other, in SSc patients. A subset of patients was selected using a 12-24-month clinically oriented interval (n = 58). The extent of ILD at HRCT was scored according to a visual semi-quantitative method (SQCT). The correlation of absolute change (Δ) in the SQCT score with change in FVC and DLco was examined using Pearson's correlation coefficient. The concordance between the OMERACT criteria (≥ 10% FVC relative decline; or 5-10% FVC and ≥ 15% DLco relative decline) and SQCT categorical change (5% and 10%) was investigated. A total of 129 patients were enrolled. During 12-24-month follow-up, ΔSQCT was negatively correlated with ΔFVC (r = - 0.487, p = 0.0001) and ΔDLco (r = - 0.298, p = 0.023). Ten patients demonstrated CT progression ΔSQCT > 5%, among whom 5 with ΔSQCT > 10%. OMERACT criteria identified 25 patients with progressive SSc-ILD, of whom only 5 presented ΔSQCT > 5 and 3 presented ΔSQCT > 10%. In conclusion, change in radiological extent of SSc-ILD was correlated to functional decline in a limited time-frame. Repeated HRCT after 12-24 months may be useful for the longitudinal characterization of ILD evolution in patients with stable pulmonary function. Conversely, functional changes are suggestive of a concurrent radiological progression only after this interval. Key Points • In SSc patients, chest HRCT performed every 12-24 months can detect minimal but significant changes in ILD extent, even in subjects with stable pulmonary function. • PFT changes in 12-24 months are related to the radiological ILD progression. • OMERACT criteria might overlook patients with radiological progression. • Repeated chest HRCT may be useful for monitoring SSc-ILD when performed within 12 to 24 months from baseline in order to promptly detect progression and possibly impact on prognosis.