Dermoscopic features of nonpigmented eccrine poromas in association with their histopathological features

Background Nonpigmented eccrine poromas (EPs) occasionally mimic various skin tumours, but their dermoscopic features have not been clarified. Objectives To evaluate the dermoscopic features of nonpigmented EPs in association with their histopathological features. Methods Retrospective analysis of the dermoscopic features of 10 histopathologically proven cases of nonpigmented EP at the Department of Dermatology, Shinshu University Hospital (Matsumoto, Japan). Results Specific features in vascular structures were observed in five of 10 nonpigmented EPs. Three cases showed a polymorphous vascular pattern: two cases of a combination of hairpin and dotted vessels, and one case of a combination of hairpin, dotted and linear-irregular vessels. In addition, there were two cases of monomorphous vascular pattern: one case of linear-irregular vessels, and one case of hairpin vessels. We did not observe arborizing, crown or comma vessels. Comedo-like openings, milia-like cysts, cerebriform pattern and ulceration were observed in one case each. Furthermore, nine of 10 cases showed the characteristic feature, described as well-circumscribed reddish globule/lacuna-like structures with separation of mesh bands, which were reminiscent of frog eggs aggregation. This characteristic feature on dermoscopy was explained by the histopathological features of horizontal sections at a depth of 300-400 mu m from the surface. Island-shaped oedematous stroma with numerous microvessels, which were surrounded by poroid cells in mesh-like forms, were seen. Conclusions Vascular structures and 'frog eggs-like appearance' are important features on dermoscopic examination of nonpigmented EP. Further studies are required to evaluate their diagnostic accuracy to differentiate nonpigmented EP from other tumours.