Development of a simplified 3-site ultrasound skin score in systemic sclerosis: a pilot study

Skin fibrosis is the hallmark of systemic sclerosis (SSc). High-frequency ultrasound is promising, but optimal measurement parameters and site selection remain uncertain. This study aimed to quantify skin thickness across multiple anatomical sites in SSc and evaluate the performance of simplified ultrasound composite scores.

A pilot study of 25 SSc patients and 25 controls was conducted at Cairo University. Modified Rodnan skin score (mRSS) and Medsger severity score were recorded. Using an 18-MHz probe, epidermal, dermal, and total skin thickness (TST) were measured at the finger, the hand, the dorsal forearm, the volar forearm, the arm, the leg, the thigh, and the back. Composite scores based on dermal thickness and TST were constructed. Inter-rater reliability was assessed using intraclass correlation coefficient (ICC).

Epidermal thickness was significantly increased in SSc at most sites. However, inter-rater reliability was poor, limiting its clinical utility. Dermal thickness showed limited discrimination between groups, whereas TST demonstrated consistent differences at the finger, the hand, and the forearm regions. While the upper back distinguished SSc from controls, reliability at this site was poor. Reduced-site composite scores outperformed extended scores, with the 3-site TST score (finger, hand, dorsal forearm) showing the best balance between diagnostic performance (AUC = 0.818) and reproducibility (ICC = 0.751). TST-based composite scores correlated positively with mRSS and Medsger severity score and differentiated diffuse from limited SSc.

The simplified three-site composite score appears to offer a feasible and reasonably reproducible approach for skin assessment in SSc. These findings are exploratory and require validation in larger cohorts.