Assessment of skin fibrosis in a murine model of systemic sclerosis with multifunctional optical coherence tomography.

Significance: Systemic sclerosis (SSc) is a chronic idiopathic disease that causes immune dysregulation, vasculopathy, and organ fibrosis that affects more than 3 million people in the US alone. The modified Rodnan skin score (mRSS) is the current gold standard for diagnosing and staging skin fibrosis in SSc. However, mRSS is subjective, requires extensive training, and has high observer variability.

Aim: We aim to provide a quantitative method for the assessment of fibrosis.

Approach: We utilized optical coherence tomography (OCT), its extensions, optical coherence elastography (OCE), and OCT angiography (OCTA) to evaluate SSc-like fibrosis and therapy response in a mouse model.

Results: We showed stiffness differences between fibrotic and normal mouse skin by week 4 ( $p=0.02$ ) during the longitudinal study. In the treatment response study, OCE recorded higher elastic wave velocity in untreated fibrotic skin ( $p=0.04$ ). Treated fibrotic skin stiffness was between normal and fibrotic levels. OCTA indicated significantly dilated microvasculature in fibrotic skin versus control ( $p\ll 0.01$ ), with more dilation in the treatment group ( $p\ll 0.01$ ) than in normal skin.

Conclusions: Our results indicate that OCT and its extensions effectively analyze dermal fibrosis. OCE revealed increased stiffness in fibrotic skin, OCTA showed vessel dilation, and OCT noted morphological changes in fibrosis tissue.