Clear cell syringofibroadenoma (of Mascaro) of the nail.

Eccrine syringofibroadenoma (ESFA) is a rare disorder. We report the first case of ESFA of the nail apparatus, which presented as a yellow longitudinal onycholytic band of the left fourth finger over an intermittently painful subungual filamentous tumour. Histological examination showed features of ESFA with a digitate pattern of papillomatosis due to the specialized physiological longitudinal arrangement of the ridges in the nail bed. In addition, we describe a new feature of colloidal iron-positive clear cells. In our case, the presence of two types of cells with a central ductal differentiation and a significant amount of mucopolysaccharides in clear cells could suggest differentiation towards both the ductal and the secretory portion of the eccrine gland.