Facial lesion that came “out of nowhere”

Differential diagnosis

The differential diagnosis of the underlying causes of cutaneous horns is extensive. Some causes are listed in the Table ; common ones include actinic keratoses (25%–35% of patients with cutaneous horns), verruca vulgaris (15%–25%), and cutaneous malignancies (15%–40%).¹

Features that have been reported to increase the chance of an underlying malignancy include older age, male sex, lesion geometry (either alarge base or a large height-to-base ratio), and presence on a sun-exposed location (face, pinnae, dorsal hands and forearms, scalp). More than 70% of cutaneous horns with underlying premalignant or malignant lesions are found on these sun-exposed areas.^3,6 Additionally, cutaneous horns on these locations are twice as likely to harbor underlying premalignant or malignant lesions.⁶ Of patients with malignancies underlying their cutaneous horns, up to one third have a history of skin malignancy.⁷

TABLE
Some causes of cutaneous horn