High frequency ultrasound of skin involvement in systemic sclerosis - a follow-up study

Introduction: High-frequency ultrasound offers a potential for objective and quantitative assessment of skin thickness and skin echogenicity in systemic sclerosis (SSc). Few studies have however assessed the longitudinal changes of skin involvement using ultrasound. The aim of the study was to investigate changes in skin thickness in early SSc using high frequency ultrasound during one year of follow-up in comparison to other measurements of skin fibrosis. Methods: This retrospective study comprised 75 consecutive patients with disease duration shorter than 3 years, in whom ultrasound examination of skin thickness was performed at baseline and at the one year follow-up at five predefined sites. Results: Repeated ultrasound examination identified significant changes in a majority of patients. In 21 patients, the total sum of skin thickness (TST) increased, while TST decreased in 37 patients. On a group level there were significant decreases in skin thickness of the chest (p = 0.024) and in the TST (p = 0.011) during the observation time. Both baseline and follow-up TST correlated to serum-COMP (r(S): 0.41; p = 0.001; r(S): 0.49; p < 0.001), modified Rodnan skin score (mRSS; r(S): 0.48; p < 0.001; r(S): 0.48; p < 0.001) and hand mobility in scleroderma (HAMIS; r(S): 0.30; p = 0.043; r(S): 0.64; p < 0.001). Changes in TST correlated with changes in serum-COMP (r(S): 0.30; p = 0.034), changes in mRSS (r(S): 0.43; p < 0.001) and changes in HAMIS (r(S): 0.53; p = 0.001) during follow-up. Conclusions: In early SSc, skin thickness measured by high frequency ultrasound develops in parallel with serum-COMP, mRSS and the HAMIS test. Ultrasound examination of the skin allows for objective assessment of one facet of the complex process of skin fibrosis in early SSc.