Objective: Our objective was to develop a 17-site ultrasound method of measuring skin thickness in patients with systemic sclerosis (SSc) and to assess its inter- and intra-observer variability.
Methods: Dermal thickness (using a 22 MHz ultrasound probe) was measured at 17 sites (corresponding to those assessed in the modified Rodnan skin score) in 39 patients with SSc (26 limited cutaneous, 13 diffuse) and 34 healthy controls. The sum of the thicknesses (at the 17 sites) and the maximal thickness were also documented. Because skin thickness varies between sites, each measurement was converted to a z-score. Inter- and intra-observer variability were assessed in 35 patients/33 controls, and 20 patients/15 controls respectively.
Results: Measurement precision was good for the dermal measurements-intraclass correlation coefficients at the 17 sites ranged from 0.65 to 0.94 for the inter-observer variability (0.86 for maximum thickness) and from 0.55 to 0.96 for the intra-observer variability (0.92 for maximum thickness).
Conclusion: Our results suggest that the 17-point dermal ultrasound scoring system is extremely reliable and may therefore be a useful measure of outcome, including in clinical trials.