Histopathology of solar lentigines of the face: A quantitative study

Background: Solar lentigines are acquired pigmented lesions on sun-damaged skin that in general have both keratinocytic and melanocytic hyperplasia, but no melanocytic atypia and no nests of melanocytes. Most histopathologic studies of solar lentigines have been limited to sites other than the face and have not included a systematic and quantitative assessment of the diagnostic features. Objective: Our purpose was to systematically quantitate a variety of histologic parameters that may be useful in the diagnosis of facial solar lentigines. Methods: We retrospectively evaluated 51 solar lentigines from 51 patients. This included a review of the hematoxylin-eosin, Mel-5 immunoperoxidase, and Fontana-Masson stains to quantify melanocytes (per millimeter), melanin content of the epidermis, and epidermal area by means of a computer-assisted image analysis program. Results: Lentigines from the face often had a flattened epidermis (25 of 51). They also had a mean 2.1-fold increase in melanocytes (p < 0.001), a 2.1-fold increase in epidermal area (p < 0.001), and a 2.2-fold increase in epidermal melanin content (p < 0.001) compared with normal photoexposed facial skin. Conclusion: Facial solar lentigines had a statistically significant twofold increase in both epidermal area and number of melanocytes compared with facial skin with a similar degree of photodamage, but frequently lacked the rete ridge hyperplasia classically associated with lentigines from other anatomic sites. These morphologic data may be helpful in the evaluation of biopsy specimens from pigmented lesions on photodamaged facial skin.