Influence of contextual factors and reliability of ultrasound skin measures in persons with systemic sclerosis and healthy controls.

OBJECTIVES: To examine the influence of contextual factors upon the evaluation of skin thickness and stiffness by ultrasound and to assess the reliability of these parameters.

METHODS: Ultrasound dermal thickness (by B-mode, 18MHz) and skin stiffness (by shear-wave elastography, 9MHz) were assessed in persons with systemic sclerosis (SSc) and in healthy controls. The influence of contextual factors upon repeated measures was evaluated: (i) room temperature (16-17ºC vs. 22-24ºC); (ii) time of day (morning vs. afternoon), and (iii) menstrual cycle phase (menstrual vs ovulatory). Differences were analysed using the related-samples Wilcoxon signed-rank test. Inter- and intra-rater reliability of ultrasound skin thickness and stiffness were evaluated in the 17 skin Rodnan sites of 20 persons with SSc and 20 healthy controls, under stable contextual conditions.

RESULTS: A significant increase in ultrasound dermal thickness was observed at the leg in the afternoon vs morning, in both patients and controls. Similar observations were made for skin stiffness at the leg (in SSc) and at the foot (in SSc and controls) in the afternoon. No significant changes were observed in association with room temperature and menstrual cycle. Intra- and inter-rater-reliability was good to excellent for ultrasound dermal thickness and stiffness, both in SSc and healthy controls.

CONCLUSIONS: The timing of the ultrasound procedure within each day seems to influence the ultrasound measures at the legs and feet. Our study corroborates that ultrasound dermal thickness and skin stiffness are reliable domains to quantify skin involvement in SSc.