**3.5 Scleroderma**

One of the most important clinical features of patients with systemic sclerosis (SSc) is the skin thickening. The extent of skin features in SSc is divided clinically into diffuse and limited involvement and is usually quantified using the Rodnan skin score. In addition to this, high-frequency ultrasound can also allow for a detailed assessment of skin involvement. The target measurement is the dermal thickness. For a correct assessment, the following interfaces need to be identified: surface–epidermis, epidermis–dermis and dermis–subcutis [53]. Skin features in SSc vary in time and this is detectable also through US. In the edematous phase, increased thickness associated with low echogenicity is seen due to water content. In time, fibrosis leads to increased echogenicity. Ultrasound measurements correlated well with histopathology, Rodnan skin score and EUSTAR disease activity index [5, 54]. Hongyan and colleagues defined an optimal cutoff point of 7.4 mm for skin thickness, with a sensitivity of 77.4% and specificity of 87.1% [54]. Quantitative studies of skin stiffness using sonoelastography yielded promising results. Research by Yang and colleagues indicates that Shear Wave Elastography can discriminate between SSc patients and controls (**Figure 11**), has good reliability and correlates well with skin thickness and modified Rodnan skin sore [55].
