A 45-year-old woman brings her daughter for evaluation of the daughter’s acne. However, during the appointment, an odd lesion is noted on the mother’s shoulder.
Once the daughter’s evaluation is completed, attention turns to the mother’s lesion, which she reports “has been there for years.” Until last year, it hadn’t changed—but since then, it has grown considerably and also darkened.
The patient has an extensive history of poorly tolerated sun exposure in her childhood and young adulthood. She says she is able to tan but “it only holds for a short time.”
The lesion, a 2.8-cm black plaque with irregular margins, is located on the crown of the right shoulder. The patient has somewhat sun-damaged, freckled type II skin.
Dermatoscopic examination reveals regularly spaced white pinpoint areas scattered over the lesion’s surface. Focally, there is definite black streaking and pigment clumping on the borders of the lesion.
The white spots are consistent with pseudocysts seen in seborrheic keratosis. But the clumping and streaming of pigment are features we might expect to see with melanoma.
What is the diagnosis?