Background/Purpose: Skin involvement in systemic sclerosis (SSc) is often primary outcome in clinical trials and its severity inversely correlates with prognosis. Nevertheless, an objective quantitative imaging biomarker to assess skin fibrosis is still lacking in SSc. Optical Coherence Tomography (OCT) is a imaging technology that measures optical density (OD) of a substrate and can provide high contrast 2 mm deep skin images with a 5-10 micron resolution. Concurrent validity and reliability of such technique to assess skin involvement in SSc have been previously reported.¹The aim of this study was to determine whether OD of the dermis as assessed by OCT could be used to quantitatively discriminate healthy skin from clinically uninvolved SSc skin and to correlate with clinical assessment of skin thickness in SSc patients (construct validity).

Methods: A total of 393 OCT scans of hands and forearms on 20 SSc patients and 15 healthy controls (HC) were performed employing topical probe “VivoSight” (Michelson Diagnostics). Matlab software was employed to calculate mean 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. Construct validity was determined by correlation with the current gold standard, the modified Rodnan Skin Score (mRss). The minimum (Min) value of OD before the dermis and the maximum (Max) value of OD in the dermis were considered to compare the forearm skin OCT mean A-scans of SSc patients and HC. ROC analysis of HC and mRSS=0 mean A-scans suggested that the OD value at 300 (± 16) micron was the one with best sensitivity/specificity ratio in discriminating HC vs clinically unaffected skin. We therefore included the mean value of OD at 300±16 micron for further analysis. Statistical analysis was performed employing Pearson correlation, one-way Anova and Bonferroni correction tests as appropriate.

Results: OCT mean A-Scans showed a different pattern in HC and four mRSS groups. SSc affected skin showed a consistent decrease of OD in the papillary dermis (PD), which caused a loss of definition of the DEJ. Max OD values of the PD in HC and the four mRSS subgroups was significantly different across the five groups (P<0.0001) and showed a significant correlation with mRSS (r=-0.69, P<0.0001). Similarly, Min OD values were significantly different across the five groups (P<0.0001) and showed a strong correlation with mRSS (r=-0.6, P=0.0002). In both cases after Bonferroni correction for multiple variables, the difference in Min and Max OD remained significant between HC or mRSS=0 and patients with mRSS=2 or 3, suggesting that these measures correlated with skin involvement but could not discriminate between HC and patients with mRSS=0 or 1. On the contrary, OD300 was significantly different between HC and patients with mRSS=0 or 1 (P<0.001).

Conclusion:

The decrease of OD in the PD in skin fibrosis as assessed by OCT is a valid quantitative outcome measure of skin fibrosis. 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 in clinical intervention trials and clinical management.

References:

1.Abignano et al. Annals Rheum Dis 2012

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/optical-density-measure-of-the-papillary-dermis-discriminates-as-abnormal-clinically-uninvolved-skin-in-systemic-sclerosis-and-correlates-with-severity-of-skin-thickness/