Fifty-year-old twin sisters are seen for what appears to be the same problem: changes in the color and texture of their neck skin, recently noted by a family member. Both deny ever noticing it before and further deny experiencing any associated symptoms.
The sisters are accompanying their mother, who is being treated for basal cell carcinoma. All three women grew up living and working on the family farm, spending a great deal of time in the sun from an early age.
EXAMINATION
Both patients have type III skin, meaning that they seldom burn, tan fairly easily, and are able to keep that tan. The patients have identical, obvious hypo- and hyperpigmentation covering the sides of their faces and necks, sparing a well-defined oval area on the submental anterior neck.
The affected areas appear hyperemic, displaying a reddish brown tinge, but fail to blanch with digital pressure. The changes are completely macular.
What is the diagnosis?