Chapter 10: Melanocytic Proliferations

A 30-year-old Caucasian male presents with multiple stellate brown macules on the shoulder after a severe sunburn from last summer. The lesions are all of about the same size and are sharply marginated. A biopsy is performed and the findings are illustrated below. Melan-A stain reveals a normal concentration of intraepidermal melanocytes. Which of the following diagnoses is CORRECT?

A) Pigmented actinic keratosis

B) Lentigo maligna melanoma

C) Solar lentigo

D) Junctional melanocytic nevus

E) Freckle

The correct answer is C.

Solar lentigo occurs on sun-exposed skin in more than 90% of the white population older than age 60 years but may be observed in much younger individuals as well. Solar lentigines are distinguished from common freckles by their persistence despite absence of sun exposure. Solar lentigines are prominent in xeroderma pigmentosum. The photochemotherapy-induced (PUVA) lentigo has been observed in patients receiving long-term methoxypsoralen PUVA for psoriasis. Carriers of one or two of the melanocortin-1-receptor (MC1R) gene variants have a 1.5- to 2-fold increased risk for the development of numerous solar lentigines. Clinically, solar lentigines are well-circumscribed, round, oval, or irregularly bordered macules of yellow, tan, or brown color, varying in size from about 1 to 3 cm in diameter, with a tendency to confluency. Solar lentigines occur on sun-exposed areas, predominantly the dorsal aspects of hands and forearms, the face, and the upper chest and back. The “sunburn,” hypermelanotic, or “ink spot” solar lentigo is characterized by a striking jet-black color and a stellate outline. The PUVA lentigo has a close clinical resemblance to the solar lentigo, particularly the hypermelanotic type.

Microscopically, in general, the solar lentigo is characterized by increased melanin pigment ...