Performance of ultra-high-frequency ultrasound in the evaluation of skin involvement in systemic sclerosis: a preliminary report

Objective. High frequency ultrasound allows visualization of epidermis, dermis and hypodermis, precise measurement of skin thickness, as well as assessment of skin oedema, fibrosis and atrophy. The aim of this pilot cross-sectional observational study was to assess the performance and multiobserver variability of ultra-high-frequency (UHF) (50 MHz) ultrasound (US) in measuring skin thickness as well as the capacity of UHF-derived skin features to differentiate SSc patients from healthy controls. Methods. Twenty-one SSc patients (16 limited and five diffuse SSc) and six healthy controls were enrolled. All subjects underwent US evaluation by three experts at three anatomical sites (forearm, hand and finger). Dermal thickness was measured and two rectangular regions of interest, one in dermis and one in hypodermis, were established for texture feature analysis. Results. UHF-US allowed a precise identification and measurement of the thickness of the dermis. The dermal thick- ness in the finger was significantly higher in patients than in controls (P<0.05), while in the forearm it was significantly lower in patients than in controls (P<0.001). Interobserver variability for dermal thickness was good to excellent [forearm intraclass correlation coefficient (ICC) = 0.754; finger ICC= 0.699; hand ICC = 0.602]. Texture computed analysis of dermis and hypodermis was able to discriminate between SSc and healthy subjects (area under the curve >0.7). Conclusion. These preliminary data show that skin UHF-US allows a very detailed imaging of skin layers, a reliable measurement of dermal thickness, and a discriminative capacity between dermis and hypodermis texture features in SSc and healthy subjects.