Systemic sclerosis (SSc) is a rare autoimmune disorder. It is characterized by fibrosis and vascular obliteration in the skin and other organs. Skin damage, manifested by thickening of the skin tissue, is often one of the first signs of the disease. Pathogenesis is dominated by early microvascular changes targeting endothelial cells and with the release of several mediators promoting an inflammatory response and vascular remodeling. This inflammatory cascade results in fibrosis lesions. Early diagnosis of fibrosing skin lesions is essential in SSc since their severity is correlated with functional prognosis and survival. To date, there is no validated tool to reliably quantify skin fibrosis. The semi-quantitative Modified Rodnan score (mRSS), based on clinical assessment of skin thickening at 17 anatomical areas, is widely used. The main limitation of this method is its inter-operator variability. The histopathological analysis of the skin biopsy is interesting but invasive. The new non-invasive and reproducible tools are needed to evaluate skin fibrosis for early diagnosis of SSc.

Optical coherence tomography (OCT) is an innovative imaging technique that uses a light wave to capture 3D images of a material that scatters light. OCT allows real-time, direct and high-resolution imaging of the morphology of the biological sample (such as skin) without ionizing radiation. In SSc, the cutaneous fibrosis is characterized by a deregulated production of the components of the extracellular matrix, in particular collagen. Previous results showed that the dermal-epidermal junction could be observed in healthy subjects using OCT. In patients with SSc and skin involvement, the visualization of this junction could be reduced. The results suggest a possible correlation between the intensity of visualization of the dermo-epidermal junction and the severity of cutaneous fibrosis.

In this project, we would like to compare the skin involvement of the dorsal surface of a finger between patients with early SSc and control subjects using non-invasive OCT imaging. The study population meets the criteria for early SCS, with onset of disease less than 2 years and without clinically detectable skin involvement. In a second time, other imaging techniques (HD ultrasound) or fluid silicone molding technique will be used to evaluate the progression of skin fibrosis or the morphological characteristics of the skin or vascular network of the patient with early SSc. To complete the work, these parameters will be evaluated in other anatomical sites (outer and inner side of the forearm) or in another group of patients (Established SSc patients with clinical cutaneous sclerosis) or at another timepoint (M24). The hypothesis of this study is that OCT can be used to identify SSc patients at a stage where the lesions are still early and reversible.

This is a prospective, monocentric, comparative, open-label and longitudinal patient study with duration of 36 months. The duration of the inclusion period will be 12 months. The participation of each subject is from 1 hour (for group 2 and 3) to 24 months (for group 1). We planned to include 60 patients in the Department of Rheumatology of the University Hospital of Strasbourg (20 patients from each group).

The different measures in the study are not invasive. No specific biological sampling of the study will be conducted. There will be no change for the treatment of patients either.