Reliability of ultrasound measurements of dermal tickness at digits in systemic sclerosis: role of elastosonography

OBJECTIVES: To investigate the role of elastosonography to improve the reliability of the ultrasound in the measurement of the dermal thickness at finger level in systemic sclerosis (SSc). METHODS: Twenty-two patients with a diagnosis of SSc were consecutively recruited. In all patients at the second finger level of the dominant hand the dorsal aspect of proximal and middle phalanx was assessed in grey-scale and also using the elastosonography by an experienced musculoskeletal sonographer. The first step of the study was directed to explore the correlation between measurements of the dermal thickness using the grey-scale and elastosonography. Subsequently, the intra and the inter-reader reliability (between the sonographer who performed the ultrasound study and another sonographer) in the ultrasound measurements of the dermal thickness was assessed. Intra and inter-reader reliability was calculated using intra-class correlation coefficient (ICC) and illustrated by Bland-Altman plots. RESULTS: The ICC values were 0.904 and 0.979 for the intra-observer agreement, and 0.726 and 0.881 for the inter-observer agreement, using only the grey-scale and also the elastosonography, respectively. An excellent correlation was obtained between measurements in grey-scale and adopting the elastosonography by the experienced sonographer (rho=0.99), while the rho values between the two readers were 0.59 and 0.88, using the conventional technique and also the elastosonography, respectively. CONCLUSIONS: Elastosonography can improve the reliability of the US measurements of the dermal thickness at finger level in patients with SSc, helping for the identification of the interface dermis/hypodermis.