Phacomatosis pigmentokeratotica: a 20-year follow-up with malignant degeneration of both nevus components.

Phacomatosis pigmentokeratotica is a rare syndrome defined by the association of an organoid nevus occasionally with sebaceous differentiation, a speckled lentiginous nevus, and other extracutaneous anomalies. The disorder is a consequence of the so-called twin spot genetic mechanism. We describe the first occurrence involving malignant degeneration of both nevus components, giving rise to three basal cell carcinomas over the sebaceous nevus and a malignant melanoma of the superficial spreading type over the speckled lentiginous nevus. This observation, in concert with the other instances reported in the literature, points to the need for adequate patient follow-up to ensure early detection and treatment of any possible associated malignant degeneration.