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 μm 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.