ABSTRACT
Clinically, DN may exhibit any or all of the features commonly attributed to melanoma: asymmetry, border irregularity, color variation, diameter larger than 5 millimeters, and, as DN are acquired nevi, the patient may identify the lesion as new or evolving. They can be completely amelanotic, deeply
pigmented, or both.15,16 DNs usually develop on the trunk, especially the upper back, in teens or younger adults, and on the legs of women, but they can appear anywhere and at earlier ages especially in the familial form, where they may appear on the scalp before puberty.16-18
Dermoscopically, DN are heterogenous. They can show reticular, globular, or brown structureless (homogenous) patterns or, most commonly, a combination of these. DN can also be classified dermoscopically by pigment distribution: eccentric hyper-or hypopigmentation, central hyper-or hypopigmentation or multifocal hyper-or hypopigmentation.19,20 Importantly, while DN show overlapping dermoscopic features with melanoma and can show multicomponent patterns, their architectural structures appear orderly as compared to the disorder seen in melanoma.7,8
On histology, DN show a proliferation of cytologically atypical melanocytes in solitary units and
variably sized nests along the sides and tips of rete ridges with associated bridging of adjacent rete ridges, concentric or lamellar fibroplasia, and an associated superficial mononuclear cell infiltrate. If the lesion is compound, nested melanocytes are present in the superficial dermis and the junctional component extends laterally beyond the dermal component, creating a “shoulder.” Typically, DN show a lentiginous pattern with many solitary melanocytes as well as smaller nests of melanocytes along the rete ridges, which are elongated and pigmented. In this scenario, melanin pigment often also extends beyond the basal layer and may be present at all layers of the epidermis focally or diffusely, causing the lesion to appear brown or black clinically. Compact hyperkeratosis is not uncommon in these lesions. Occasionally DN show a predominantly nested pattern. These DN may show Spitzoid cytology, with abundant eosinophilic, dusty, or pigmented cytoplasm and an enlarged oval nucleus containing a prominent nucleolus.21 DN can also show some congenital features with slightly deeper extension around adnexal structures in the dermis. DN are also usually organized, well formed, and quite symmetrical, though with increasing atypia, these features may be absent.4,5,21-23 Upward scatter of melanocytes is tolerated but should be limited to the center of the lesion unless the lesion is irritated either from trauma/rubbing or from exogenous factors such as ultraviolet (UV) radiation. Clues to irritation include parakeratosis, necrotic keratinocytes, erosion, or ulceration. When due to irritation, melanocytes scattered above the basal layer should be evenly dispersed and uniform. Unfortunately, irritated nevi can show diffuse upward scatter of melanocytes, a concerning feature normally attributed to melanoma. In this situation, one must combine the clinical history as well as evidence of irritation and the distribution of melanocytes to avoid over-or under-calling the lesion.24-28
Several different methods have been proposed to grade the atypia of DN with limited interobserver reproducibility.4,5,29 Of these, the Duke criteria,
introduced by Shea and colleagues, offers a scheme that takes into account both cytological atypia and architectural disorder, using a methodical point system.33 As such, the Duke criteria provide a more broadly descriptive scoring system that accounts for most of the criteria that can overlap between nevi and melanoma, making it more objective and reproducible, and thus particularly amenable to statistical analysis.
