Clinical Dermatology

Diagnostic Hallmarks

1. Distribution: random but with some predilection for sun-exposed skin
2. Size: 3 to 7 mm
3. Round and evenly pigmented
4. Long history of unchanged appearance

Clinical Presentation

Nevi are pigmented lesions that may be flat (junctional) or elevated (compound and intradermal). They generally vary in color from light brown to dark black, but some intradermal nevi in older adults are so lightly pigmented as to appear skin colored. They range in size from 2 to 10 mm, but most are 3 to 7 mm in diameter. For the most part, nevi are remarkably round, evenly pigmented, and soft on palpation.

Nevi may be found anywhere on the body, including the scalp, palms, soles, mucous membranes, and nail matrix. They are, however, more numerous on sun-exposed surfaces. Everyone except true albinos have one or more nevi, and in some people hundreds may be present. Junctional nevi, because of their Hatness, may be confused with freckles and lentigines, but the junctional nevus tends to be larger, darker, and more perfectly round. One or more nevi may be present at birth (congenital nevus), but most develop during the childhood years. Surprisingly, development of new nevi in mid and late adult life is more common than was previously thought. Nevi in children are predominantly junctional, whereas nevi in adults are more likely to be compound or intradermal.

The diagnosis of a benign nevus is generally possible on a clinical basis. Pigmented lesions that cannot be reliably recognized as benign should be biopsied.

Course and Prognosis

Nevi are very stable lesions. Once present, they change very little in size or color. Over a lifetime, however, it is believed, nevi may pass through successive stages of junctional, compound, and intradermal development. Evidence that this occurs is based primarily on the predominance of junctional nevi in children and of intradermal nevi in older adults.

The odds that anyone nevus will undergo malignant degeneration are very small, probably on the order of 1 in 100,000. Unfortunately, except for dysplastic nevi, there is no way to identify prospectively which nevi will evolve into melanomas. There are some theoretical reasons to believe that chronic trauma might increase the risk of melanoma development, and for this reason some physicians have in the past recommended prophylactic removal of nevi from palms, soles, genitalia, and belt lines. At the practical level, however, I here is no evidence to support this belief, and since 10% of the population have nevi in such locations, it is clear that removal of all such lesions would be quite impractical.

Pathogenesis

The constituent cells of pigmented nevi are called nevus cells. Nevus cells are presumably derived from melanocytes that migrated to the epidermis from the neural crest during early fetlal development. The transition from melanocytes to nevus ,ells appears to involve a “rounding-up” and loss of dendritic processes, as the cells proliferate in a clustered or nest-like pattern. Pigment production in nevus cells appears identical with that of melanocytes.

In junctional nevi the clusters of nevus cells are found ,solely at the dermal-epidermal junction. In compound nevi the clusters of nevus cells are located both at the dermal-epidermal junction and within the upper portions of the dermis. In intradermal nevi the nests of nevus cells appear solely within the dermis. As stated above, it is possible that there is progressive evolution from one stage to the next.

The significance of nevi and d1e reasons for their development are unknown. Since everyone has them, and since some of them develop during fetal life, it is tempting to consider them as normal components of human skin. On the oilier hand, there are also several reasons to consider them as pailiologic processes. First, they continue to develop in post fetal life. Second, their distribution seems gready influenced by patterns of ultraviolet light exposure. Third, from time to time the body mounts a lymphocytic, destructive attack against them in the process clinically recognized as halo nevus information. Finally, some of the large congenital nevi have an unusually high rate of malignant transformation on.

Therapy

Normal nevi need not be removed regardless of their location. Lesions that demonstrate one or more atypical characteristics and those that are cosmetically unacceptable, however, can be removed in a variety of ways. Most dermatologists favor the use of shave biopsy for reasons of simplicity and freedom from scarring. This approach works well for middle-aged and older adults. Unfortunately, in younger patients, shave biopsy is followed by a very high recurrence of speckled pigmentation. This recurrence is disturbing to doctor and patient alike, as it raises the question of a malignant process. For this reason I generally prefer excision with suture closure in young patients. I believe that all nevi should be histologically examined at the time of removal and thus am opposed to the destruction of such lesions with electrosurgery, cryosurgery, or chemocautery

This entry was posted on Wednesday, November 7th, 2007 at 11:50 am and is filed under Lesions. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.