Label-free differentiation of classical and hypermobile Ehlers-Danlos syndromes using Mueller matrix polarimetry

Diagnosing classical and hypermobile Ehlers-Danlos syndromes, cEDS and hEDS, respectively, remains challenging due to overlapping clinical presentations and the lack of objective diagnostic tools. A label-free quantitative method for detecting EDS from normal tissues and for distinguishing its subtypes could support more timely and accurate clinical evaluation.

We evaluate the capability of Mueller matrix (MM) polarized light microscopy to resolve polarimetric contrasts between healthy and EDS samples and to assess its potential for differentiating between the cEDS and hEDS subtypes.

Unstained skin biopsy slides from 19 participants (healthy, $n=3$ ; cEDS, $n=5$ ; hEDS, $n=11$ ) were imaged using a custom MM microscopy setup. In addition to acquiring 16 MM elements, 24 polarimetric parameters were obtained and tested for their detection and differentiation abilities. Group-wise comparisons of median parameter values were performed after assessing distribution normality using the Shapiro-Wilk test, applying either the Mann-Whitney U test or the independent-samples $t$ -test as appropriate.

Three polarimetric parameters ( $P_L$ , $\beta$ , and $\psi$ ) showed statistically significant differences between EDS-affected and healthy skin, with higher $P_L$ values observed in healthy tissue, consistent with more uniform collagen alignment in healthy subjects. Five parameters ( $P_L$ , $r_L$ , $P_1$ , $P_3$ , and $P_{\mathrm{tms}}$ ) significantly differentiated cEDS from hEDS, with $r_L$ demonstrating the strongest separation. $P_L$ was the only parameter to show statistical significance for both tasks.

MM polarimetry shows promise for label-free, quantitative assessment of skin collagen organization and offers potential for detecting EDS and differentiating its subtypes.