Abstract
Polarisation-sensitive optical coherence tomography (PS-OCT) offers a novel, non-invasive method of assessing skin fibrosis in the multisystem disease systemic sclerosis (SSc) by measuring collagen retardance. This study aimed to assess retardance as a biomarker in SSc. Thirty-one patients with SSc and 27 healthy controls (HC) underwent PS-OCT imaging. ‘Skin score’ was assessed by clinical palpation (0–3 scale). A subset of ten patients and ten age/sex-matched HC had a biopsy and longitudinal imaging. Histological assessment included quantification of epidermal thickness, collagen content (to assess fibrosis) and matrix metalloproteinase (MMP) activity (in situ zymography). PS-OCT images were assessed for epidermal thickness (structure) and fibrosis (retardance). Positive correlation was observed between epidermal thickness as measured by histology and structural PS-OCT (r = 0.79; p < 0.001). Retardance was: HC mean 0.21 (SD 0.21) radian/pixel; SSc skin score 0, 0.30 (0.19); skin score 1, 0.11 (0.16); skin score 2, 0.06 (0.12); skin score 3, 0.36 (0.35). Longitudinal retardance decreased at one-week across groups, increasing at one-month for HC/skin score 0–1; HC biopsy site retardance suggests scarring is akin to fibrosis. Relationships identified between retardance with both biopsy and skin score data indicate that retardance warrants further investigation as a suitable biomarker for SSc-related fibrosis.
Highlights
Polarisation-sensitive optical coherence tomography (PS-Optical coherence tomography (OCT)) offers a novel, non-invasive method of assessing skin fibrosis in the multisystem disease systemic sclerosis (SSc) by measuring collagen retardance
When grouped into healthy controls (HC), skin scores 0–1 and 2–3 there is a trend for increased retardance with increasing fibrosis (Fig. 4a)
In this study we have, for the first time in SSc, utilised both structural and retardance images from Polarisation-sensitive optical coherence tomography (PS-OCT) in vivo imaging to assess the skin of patients with SSc
Summary
Polarisation-sensitive optical coherence tomography (PS-OCT) offers a novel, non-invasive method of assessing skin fibrosis in the multisystem disease systemic sclerosis (SSc) by measuring collagen retardance. Optical coherence tomography (OCT) takes non-invasive, in vivo, ‘optical biopsy’ images of the skin, analogous to ultrasound, but using light to visualise skin s tructure[9] This allows high resolution (< 10 μm) measurement of epidermal thickness. Polarisation-sensitive optical coherence tomography (PS-OCT) offers a novel non-invasive method of assessing skin fibrosis in SSc. The fibrillar collagens, a key component of the dermal extracellular matrix, cause skin to be anisotropic and to have birefringent properties (i.e. skin has different refractive indices depending on the polarisation state of the light, causing one light polarisation state to travel faster through the tissue than the other). The retardance of a material is the change in the phase angle as the light travels through and is generally shown as cumulative colour maps of in depth images
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