How much of skin improvement over time in systemic sclerosis is due to normal ageing? A prospective study with shear-wave elastography

BACKGROUND: Measurement of skin involvement is essential for the diagnosis and assessment of prognosis and disease progression in systemic sclerosis (SSc). The modified Rodnan skin score (mRSS) is the gold standard measure of skin thickness, but it has been criticised for the lack of objectivity, poor inter-observer reproducibility and lack of sensitivity to change. Recently, shear-wave elastography (SWE) emerged as a promising tool for the objective and quantitative assessment of the skin in SSc patients. However, no studies have evaluated its sensitivity to change over time. OBJECTIVE: To assess changes in skin stiffness in SSc patients using SWE during a 5-year follow-up. METHODS: Skin stiffness [i.e. shear-wave velocity values (SWV) in metres per second] was assessed by SWE ultrasound (using virtual touch image quantification) at the 17 sites of the mRSS, in each participant, at baseline and follow-up. mRSS was performed at both time points. Differences between groups were analysed using the related-samples Wilcoxon signed-rank test and the Mann–Whitney U test. RESULTS: We included 21 patients [85.7% females; mean age 56.3 (10.4) years at baseline, 57.1% with limited SSc] and 15 healthy controls [73.3% females; mean age 53.6 (14.1) years)]. The median follow-up was 4.9 (0.4) years. Skin stiffness decreased significantly at all Rodnan sites (p ≤ 0.001) (except in the fingers), in SSc patients, over time. The same phenomenon occurred in controls, but to a lesser degree, in terms of percentage change. The percentage reduction in skin stiffness varied in the different Rodnan sites and in different phases of the disease. In addition, SWV values also decreased significantly in 15/16 skin sites with local normal Rodnan at baseline, whereas local Rodnan skin score only changed significantly in the upper arm (p = 0.046) and forearm (p = 0.026). CONCLUSION: This study provides first-time evidence suggesting that skin SWV values are more sensitive to change over time than mRSS and reduce significantly over time in SSc and normal controls.