Keratoacanthoma developing on a pigmented patch in incontinentia pigmenti.

Cutaneous manifestations of incontinentia pigmenti (IP) have classically been described as three sequential stages: an initial vesicobullous stage, a verrucous stage and a stage of swirled pigmentation. Verrucous lesions tend to last longer than vesicobullous eruptions, often persisting until 1 year of age. However, adult patients with verrucous lesions are rare. We report a case of keratoacanthoma with marked dyskeratosis on a pigmented patch in a 20-year-old woman. This tumor, like subungual keratotic tumors of IP, might have been developed as one of the late manifestations of the disease.