Skin Disorders Guide

Diagnostic Hallmarks

1. Distribution- sun-exposed surfaces of the face, hands, and
2. shoulders
3. No seasonal venation in pigment density
4. Size: 5 to 20 mm
5. Occurrence in adults

Clinical Presentation

Lentigines (singular- lentigo) are brown macules 5 to 20 mm in diameter. The brown hues vary in intensity from tan to brown-black. They occur singularly or as multiple, closely set (but not cont1uent) lesions on chronically sun-exposed skin. They are particularly common on the cheeks, dorsal surface of the hands, and top portion of the shoulders. Unlike freckles, lentigines do not appear until mid adult life, and their pigmentation is constant without seasonal variation. They are also darker in color, larger in diameter, and more irregularly shaped. Lentigines are most commonly found on fair-skinned people, but they can also develop on more darkly pigmented people.

Course and Prognosis

Lentigines are permanent lesions. Once present, continued sunlight exposure is not necessary to maintain their appearance. Those occurring on the hands, arms, and shoulders are believed to have essentially no malignant potential. For the most part, this is also true for those that occur on the face. However, a small proportion of these latter lesions do, very slowly, develop into lentigo malign a or lentigo maligna melanoma.

Atypical Manifestations. Sometimes, one or more lentigines on the face will develop small speckles of dark pigmentation superimposed on the lighter brown background of the original lesion. Biopsy of these brown-black speckles reveals appreciable proliferation and dysplasia of individual melanocytes situated in the basal layer of the epidermis. Such lesions are called lentigo malign,a (Hutchinson’s freckle) and should be considered as obligate precursors for invasive melanomas (see section on melanoma). Lentigo maligna should be excised with narrow (5-mm) margins.

The pigmented macule known as lentigo simplex can be differentiated from the actinically induced lentigines discussed above. Lentigo simplex occurs as a small (2- or 3-mm) black macule similar in appearance to a hyperpigmented junctional nevus. They occur at any time from the teenage years to late adult life, but, in contrast to actinically induced lentigines, they may be found in other than chronically sun-exposed locations. Histologically, they are similar to actinically induced lentigines, but there is more evidence of incontinent melanin in dermal melanophages. Occasionally, a few nests of junctional nevus cells will also be present. The lesions of lentigo simplex are particularly likely to be seen in individuals with the dysplastic nevus syndrome.

Pathogenesis

Lentigines mostly arise because of chronic ultraviolet light exposure. Histologically, the increased pigment is due to both :In increased activity and an increased number of individual melanocytes. There is, however, no clustering of melanocytes (nest formation) such as is seen in nevi. The keratinocytic compartment of the epidermis is also enlarged by finger-like elongation of the rete ridges.

Therapy

Those lentigines that are evenly colored throughout require no therapy. The cosmetic appearance can be improved through liquid nitrogen cryotherapy, topically applied tretinoin or bleaching. Lentigines that have black speckles within them should be biopsied. Excisional biopsy is not required, punch removal of one or more of the black speckles is sufficient. If the changes of lentigo maligna are present, the entire lesion ought to be surgically excised. Lesions containing areas of black speckling that are palpable should be totally excised, with a presumptive diagnosis of lentigo maligna melanoma