Dermal organization in scleroderma: the fast Fourier transform and the laser scatter method objectify fibrosis in nonlesional as well as lesional skin

Abstract

Scleroderma, a chronic, progressive disorder, is characterized by dermal fibrosis with collagen bundles orientated parallel to the epidermis. Simple objective parameters to evaluate disease progression and therapies are needed. We describe two methods, the laser scatter method and the fast Fourier transform (FFT), to measure collagen bundle orientation and spacing. Lesional sclerodermic skin (LS), nonlesional sclerodermic skin (nonLS), and control skin (CS) sections were evaluated for orientation ratio using the laser scatter method. The FFT was used to calculate orientation ratio, variation, and spacing of collagen bundles. Parameters were correlated with local and mean skin score measurements, on a scale of 0 (normal) to 3 (severely sclerotic). With both the laser scatter method and the FFT, orientation ratios of LS (respectively, 2.16 +/- 0.33 and 1.83 +/- 0.62) were significantly higher than CS (respectively, 1.70 +/- 0.35 and 1.38 +/- 0.15). NonLS orientation ratios (respectively, 1.92 +/- 0.15 and 1.48 +/- 0.44) were between LS and CS ratios. Orientation variation and bundle spacing of LS (respectively, 57.3 +/- 19.4 and 15.7 +/- 5.6 microm) were significantly reduced compared to CS (respectively, 73.8 +/- 15.0 and 18.9 +/- 1.9 microm). NonLS orientation ratios (respectively, 57.2 +/- 29.0 and 15.6 +/- 6.1 microm) were similar to LS. Bundles in LS are more parallel, show less variation in orientation, and are more densely packed than in CS. There was a linear correlation between mean skin score and orientation ratio. Local skin score was not linearly correlated to orientation ratio. Our findings suggest that nonLS dermis without clinical sclerosis already shows fibrotic characteristics. Both techniques were easy to use and suitable for objectifying dermal fibrosis in scleroderma lesions. FFT is more accurate and reproducible than the laser scatter method and allows simultaneous pathological evaluation of the location of the analyzed tissue sections. Future studies will need to focus on the correlation between clinical disease severity and collagen bundle characteristics.