Ultrasound for day-to-day clinical use: construction of a simple discriminator between healthy skin and thickened systemic sclerosis skin.

Objectives: Distinction of dermal thickening at fingers is paramount in recognition of systemic sclerosis (SSc). Evaluation of skin thickening by modified Rodnan skin score (mRSS) might be challenging. Simple and practical tools are needed to help distinguishing (non-) thickened skin in daily practice. High frequency ultrasonography (HFUS) can reliably measure dermal thickness (DT). In this pilot study we search for a DT cut-off value (as a simple HFUS discriminator) to distinguish between healthy control (HC) and SSc skin at the left index finger (F2L).

Methods: DT evaluated by HFUS (18MHz probe) in SSc patients (2013 ACR/EULAR criteria) was compared with HC in a cross-sectional study. A cut-off value was selected by receiver operating characteristic (ROC) curve analysis.

Results: 63 consecutive SSc patients (mean age 52±14 SD, 78% female) and 48 HC (mean age 36±14 SD, 62% female) underwent HFUS. Mean DT at F2L was 1.44 mm (± 0.39 SD) in SSc patients and 1.06 mm (± 0.19 SD) in HC. Based on ROC-curve analysis, a DT cut-off of 1.5 mm is proposed as simple HFUS discriminator between HC and SSc, at a specificity of 1 and a sensitivity of 0.32. The final model had an area under the curve of 0.83 (95%CI 0.75-0.90).

Conclusions: A simple HFUS discriminator between skin thickness of HC versus SSc, i.e., DT as measured at F2L, at a cut-off of 1.5 mm, is proposed for daily use in rheumatology clinics. Further validation should be executed through prospective multicentric cohorts.