Digital fibrokeratomas are benign acquired lesions. They are firm, more or less hyperkeratotic projections arising out of a collarette of slightly raised skin. Clinically, they resemble rudimentary supernumerary digits. Microscopically, a fibrokeratoma is composed of a core of normal appearing connective tissue covered with an acanthotic epidermis which produces a dense enveloping hyperkeratosis.
Bart RS, Andrade R, Kopf AW, Leider M. Acquired Digital Fibrokeratomas. Arch Dermatol. 1968;97(2):120-129. doi:10.1001/archderm.1968.01610080024004