Diagnostic categories of acquired melanocytic nevi


Clark nevus

Clark nevi are the most common nevi in man and, moreover, are regarded by many authors as the most relevant precursor lesions of melanoma. Clinical, dermoscopic, and histopathologic variants of Clark nevi are protean, and the differentiation of Clark nevi from melanoma in situ and early invasive melanomas is the major challenge in the realm of pigmented skin lesions. Clark nevi have been eponymically named after Wallace H. Clark, Jr., who, in 1978, first drew attention to this particular type of nevus by studying numerous melanocytic nevi in patients with concomitant melanomas. It is fair to say that Clark and coworkers originally meant that this particular type of nevus, called by them dysplastic nevus, actually represents a distinctive precursor lesion of melanoma with special implications on management and treatment of patients bearing these nevi. However, in the scientific community there is no agreement on the nature of Clark nevi, on what criteria are necessary for diagnosis, both clinically and histopathologically, and on the number of lesions which are needed to have a markedly increased risk to develop melanoma.
Clinically Clark nevi are flat to elevated or even slightly papillated pigmented lesions characterized by various shades of brown coloration, and situated on the trunk and extremities that are usually called just common junctional nevi or common compound nevi.


Miescher/Unna nevus

The well-known term dermal nevus encompasses two clinical, dermoscopic and histopathologic rather distinctive variants of benign melanocytic nevi, namely, Unna nevus (papillomatous dermal nevus) and Miescher nevus (dermal nevus of the face). Clinically, Unna nevus is a soft polypoid or sessile, usually papillomatous lesion frequently located on the trunk, arms, and neck. The clinical features of Miescher nevus are rather firm, brownish to nearly skin-colored, dome-shaped papules that occur mostly on the face. The clinical features of these two common types of benign melanocytic nevi are often quite straightforward, allowing clinical diagnosis at a glance.


Spitz/Reed nevus

Spitz/Reed nevi are well-known simulators of cutaneous melanoma from a clinical, dermoscopic, and histopathologic point of view.
The clinical features of Spitz/Reed nevi are protean; they may present as small, well-circumscribed, reddish papules, larger reddish plaques, small dark-brown to black papules, larger, rather well-circumscribed, jet-black plaques (Reed nevus) but also as verrucous plaques with variegated colors. Because of these clinical features Spitz/Reed nevi are often difficult to differentiate from melanoma by clinical criteria alone. Although these nevi occur mostly in individuals younger than 20 years of age, they may be rarely found also in the third and fourth decades.



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