Photoacoustic and high-frequency ultrasound imaging of systemic sclerosis patients

Introduction: Systemic sclerosis starts with an early phase characterized by Raynaud's phenomenon, puffy fingers/hands, autoantibodies, and a scleroderma nailfold microscopic pattern. Alterations in the nailfold microscopic pattern are not evident in all early SSc patients. Photoacoustics (PA) and high-frequency ultrasound (HFUS) could fulfill this need. The former can measure oxygen saturation while the latter can measure skin thickening. We hypothesize that photoacoustics and high-frequency ultrasound can distinguish (early) SSc patients from individuals with primary Raynaud's phenomenon (PRP) by measuring oxygenation of the fingertip and skin thickening. Methods: We compared measurements of oxygenation and skin thickness of the third finger between (early) SSc patients and PRP individuals and healthy controls. The spearman rank correlation was used to analyze an association between capillary density and oxygen saturation of the fingers. Results: Thirty-one adult subjects participated in this study: twelve patients with SSc, 5 patients with early SSc, 5 volunteers with PR, and 9 healthy controls. We found a significant difference in oxygen saturation between (early) SSc patients (80.8% +/- 8.1 and 77.9% +/- 10.5) and individuals with PRP (93.9% +/- 1.1). Measurements of skin thickening showed a significant difference in (early) SSc patients compared to individuals with PRP (0.48 +/- 0.06 mm and 0.51 +/- 0.16 mm vs. 0.27 +/- 0.01 mm). There was no significant difference between healthy and PRP individuals in oxygenation or skin thickening. Conclusion:Photoacoustic and high-frequency ultrasound could help to distinguish between (early) SSc, PRP, and healthy individuals in both oxygenation and skin thickening.