Background Skin involvement in systemic sclerosis (SSc) is often primary outcome in clinical trials but it is still orphan of a quantitative imaging technique. Optical Coherence Tomography (OCT) is an emerging imaging technology for clinical examination employing a low-intensity infra-red laser beam and providing high-contrast 2 mm deep skin images with a 4 micron resolution.
Objectives The aim of this study was to evaluate face validity and reliability of OCT in SSc.
Methods Dorsal aspect of forearms was assessed employing topical probe “VivoSight” (Michelson Diagnostics) and optics of Swept-source Fourier-Domain type with a laser wavelength of 1305±15 nm. Clinical skin involvement was determined using the mRSS. The study included 8 foreams from 8 healthy controls (HC) and 5 forearms for each group scored from “0” to “3” from 13 SSc patients. Hematoxylin-Eosin (H&E) staining was performed from forearm skin biopsy, within 1 cm of OCT scanned region, in one HC and one SSc patient (mRSS=3 on the site of analysis). Matlab software was employed to calculate mean optical density (OD) of the scans. Signal changes within epidermis (ED), Dermal-Epidermal Junction (DEJ) and dermis of SSc patients and HC were analysed and collated to a unique graph. To investigate the intraobserver and interobserver reproducibility, intraclass correlation coefficient (ICC) and limits of agreement (LoA) were calculated for the minimum value after the first peak and the maximum value of the second peak of the averaged A-scans.
Results OCT images collected in HC showed a regular hyper-reflective border of the skin surface and a homogeneous hypo-reflective epidermal layer. The papillary dermis (PD) was visualized as hyper-reflective area compared to the adjacent ED allowing the visualization of the DEJ. Mean OD data showed that DEJ was a OD nadir region between 60 and 70 micron from the surface, the PD a high density region (OD range:0.64-0.72; micron range:60-100) and the reticular dermis (RD) had a OD ranging from 0.72 and 0.4. In contrast SSc affected tissues (mRSS=3) showed no DEJ and no increase in OD in the PD which appeared with a range density of 0.61-0.56. Interestingly in SSc non-affected tissues (mRSS=0), the valley corresponding to DEJ was still visible with an almost normal OD range of the PD (OD=0.64-0.67) and an OD of the second peak lower than healthy subjects. In the remaining cases (mRSS=1 and 2) the valley after the entrance peak was still visible, however with a weaker second peak compared to healthy skin and SSc non-affected skin. Validation with H&E staining confirmed the localisation of the above mentioned density areas.In addition the results showed excellent intraobserver reliability (ICC >0.98; LoA=0.94-0.99) in both parameters measured by the same clinician on the two separate occasions. The interobserver reliability was also excellent with ICC>0.89 (LoA=0.61-0.97) in both parameters assessed by two investigators.
Conclusions This is a proof of concept validation of face validity of OCT as quantitative imaging technique of scleroderma skin. The potential of this tool is supported by an excellent reliability. Sensitivity to change ability of OCT is under evaluation to determine whether the technique could be used as outcome measure of skin involvement in SSc.
Disclosure of Interest None Declared
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