Hemosiderotic clear-cell acanthoma: a pigmented mimicker

The authors report on a case of a 65-year-old man with pigmented clear-cell acanthoma located on the right thigh. Dermoscopy disclosed a peculiar picture consisting of diffuse black pigmentation with a superficial greyish veil in the central portion, dotted-to-globular dark red-black structures mainly located at the periphery with a homogenous regular reticular arrangement; peripheral translucid desquamation. Dermoscopic features are correlated with the histology, where hemosiderin deposits present in a sheet-like arrangement in the perivascular papillary dermis and in a band-like disposition in the reticular dermis at the base of the lesion can account for the pigmented picture. The lesion arose on a trauma-prone skin site; thus the authors believe that traumatic irritation may be responsible for the clinical and dermoscopic pictures, giving rise to a reaction similar in a way to the Auspitz's sign provocated by trauma for psoriasis. Red blood cells extravasation from extremely superficialized capillaries may have led to hemosiderin deposition in the papillary and the reticular dermis.