Background Measurement of skin involvement is essential for diagnosis and assessment of prognosis in systemic sclerosis (SSc). The modified Rodnan Skin Score (mRSS) is the gold standard outcome measure for assessment of skin thickness by palpation. The mRSS has been criticised for being associated with high inter-observer variability and requiring a skilled trained investigator. There is a need therefore for a reliable and objective method to assess skin stiffness. Elastography Ultrasound (EUS) is a new, non-invasive method, which has allowed qualitative and quantitative measurements of relative skin stiffness. Recently, acoustic radiation force impulse (ARFI) with a new 3rd generation technology, virtual touch quantification (VTQ), has added a new dimension, reporting absolute values for the wave propagation speed (absolute tissue stiffness). The use of VTQ technology has never before been reported in patients with SSc.
Objectives To assess skin absolute stiffness in SSc using VTQ.
Methods Skin absolute stiffness was measured by VTQ at 5 of the 17 anatomical sites of the mRSS (forearm, hand, phalanx, leg and foot, of the dominant limb). Eight patients and eight age and gender matched controls were included in the study. Ultrasound measurements of absolute skin stiffness were compared with mRSS. Absolute skin stiffness measurements are presented as median plus interquartile ranges. Spearman correlation tests were used to calculate associations between ultrasound measurements and mRSS.
Results Absolute skin stiffness measurements were systematically higher in SSc patients vs controls in 4 out of 5 measurements sites: forearm [2.4 (0.5) vs 1.7 (0.3)], hand [3.0 (1.4) vs 2.0 (0.9)], phalanx [3.8 (3.0) vs 2.1 (0.5)] and dorsum of the foot [4.4 (3.3) vs 3.1 (1.9)]. Forearm absolute skin stiffness correlated with the total mRSS (r=0.707, p=0.002). Hand absolute skin stiffness correlated with the local mRSS for this site of analysis (r=0.609, p=0.012).figure 1 VTQ of the volar aspect of the forearm in a control (A) and in a patient with SSc (B). Skin absolute stiffness values (shear-wave velocities) are presented (m/s) (right side). Red indicates stiff tissue, green/yellow intermediate stiffness and blue low stiffness. Tissues with a higher shear-wave velocity have higher stiffness.
Conclusions VTQ is a novel and promising application of ARFI imaging. It provides a very precise quantification of absolute skin stiffness and has potential as an objective measure for skin assessment. Further studies are warranted to define the potential contribution of VTQ to the clinical evaluation and for its use as potential outcome measure of skin involvement in SSc.
References Clements PJ, et al Arthritis Rheum.1990;Iagnocco A, et al J Rheumatol. 2010;Di Geso L, et al Clin Exp Rheumatol. 2011.
Disclosure of Interest None Declared