Rheumatology Advance Access originally published online on April 25, 2008
Rheumatology 2008 47(7):1018-1024; doi:10.1093/rheumatology/ken145
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Quantification of hardness, elasticity and viscosity of the skin of patients with systemic sclerosis using a novel sensing device (Vesmeter): a proposal for a new outcome measurement procedure
1Department of Respiratory Medicine, Allergy and Rheumatic Diseases, Osaka University Graduate School of Medicine, Osaka, and 2WaveCyber Co. Ltd., Saitama, Japan.
Correspondence to: Y. Shima, Department of Respiratory Medicine, Allergy and Rheumatic Diseases, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita city, Osaka, 565-0871, Japan. E-mail: ryanjin{at}imed3.med.osaka-u.ac.jp
| Abstract |
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Objectives. No objective method to measure skin involvement in SSc has been established. We developed a novel method using a computer-linked device to simultaneously quantify physical properties of the skin such as hardness, elasticity and viscosity.
Methods. Skin hardness was calculated by measuring the depth of an indenter pressed onto the skin. The Voigt model was used to calculate skin elasticity, viscosity, visco–elastic ratio and relaxation time by analysing the waveform of skin surface behaviour. The results were compared with the modified Rodnan skin score (mRSS) obtained at 17 sites on the bodies of 20 SSc patients and 20 healthy controls. A functional assessment questionnaire was administered to determine how skin hardness represents a patient's disability. We also examined intra- and inter-observer variability to determine the reliability of this method.
Results. The crude hardness obtained with this device correlated well with the standard hardness specified by the American Society for Testing and Materials (ASTM, r = 0.957). A close relationship between hardness and total mRSS was also observed (r = 0.832). Skin elasticity correlated positively, and relaxation time negatively with mRSS. Functional disability correlated more closely with skin hardness (r = 0.643) than with mRSS (r = 0.517). Intra- and inter-observer variabilities were 7.63 and 19.76%, respectively, which were lower than those reported for mRSS.
Conclusions. Increases in hardness and elasticity as well as shortening of relaxation time constitute objective characteristics of skin involvement in SSc. The system devised by us proved to be able to assess skin abnormalities of SSc with high reliability.
KEY WORDS: Systemic sclerosis, Scleroderma, Skin hardness, Skin elasticity, Skin viscosity, Visco–elastic ratio, Relaxation time, Skin score, Sensing device, Computer-assisted device
Submitted 19 September 2007;
revised version accepted 18 March 2008.
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