Exploratory study on quantitative assessment of skin hardness in patients with systemic sclerosis using SOFTGRAM

There is a lack of quantitative and objective methods for measuring skin hardness. This study aimed to verify whether SOFTGRAM, a device that can measure elastic modulus using the Hertz elastic contact theory, could be used to evaluate skin hardness in systemic sclerosis (SSc).

Skin score according to the modified Rodnan total skin thickness score and elastic modulus of the skin using SOFTGRAM were measured for 20 patients with SSc and 20 healthy controls on 8 parts of the body, both of the cheeks, forearms, fingers, and hands. Five observers shared to measure skin score 320 times (40 participants × 8 parts). Elastic modulus was measured 1600 times (40 participants × 8 parts × 5 times each). As an additional examination to compare differences between observers, the skin score of another healthy control was measured 40 times (5 observers × 8 parts). Elastic modulus was measured 200 times (5 observers × 8 parts × 5 times each).

There was a significant correlation between elastic modulus and skin score (correlation coefficient=0.67, p<0.001) and a significant difference in elastic modulus (8 parts: healthy controls vs. limited cutaneous SSc vs. diffuse cutaneous SSc: 22.6±15.7 vs. 32.0±27.7 vs. 44.8±39.8, p<0.001). Intraobserver reliabilities were sufficient in 6 out of 7 observers; however, interobserver was less satisfactory.

This study showed the practicality of SOFTGRAM as an accurate measurement method of skin hardness but also revealed points to be improved. More studies are needed to find an accurate measurement method of skin hardness.