Acquired digital fibrokeratoma presenting as a painless nodule on the right fifth fingernail

A 53-year-old woman presented with an asymptomatic nodule on the distal subungual right fifth fingernail that had slowly enlarged over the last year. An excisional biopsy showed an acanthotic epidermis surmounted by hyperkeratotic scale as well as a fibrotic dermis with collagen bundles assuming a vertical orientation to the long axis of the epidermis, characteristic of an acquired digital fibrokeratoma (ADF). There was no sign of recurrence 4 months following excision. There are no known associations or risk factors for development of ADF, though prior trauma might play a role. This case describes the clinical and histopathological features of ADF and the differential diagnosis and treatment options. It is important to consider ADF when examining subungual nodules, and to be able to identify and differentiate between other benign and malignant nail tumors.