Quiz 3: What is your diagnosis?

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Diagnosis: Quiz 3

Quiz 3

Answer: Clark-like nevus

Criteria for diagnosis clinically:  A large, approximately 1.5 mm, ovoid lesion, tan and barely raised in its center and fawn-colored at its macular periphery is a Clark-like nevus.

Differential diagnosis clinically: The possibility of this being an authentic Clark's nevus must be considered seriously because despite the large size-the lesion is mostly flat. Yet another diagnostic consideration is that this nevus is a distinctive type yet to have been characterized precisely, it being neither a true Clark's nevus nor a superficial congenital nevus.

Criteria for diagnosis histopathologically: A symmetrical, well-circumscribed, proliferation of melanocytes, typified at the dermoepidermal junction by an increase in number of melanocytes disposed as solitary units and organized in nests and in the dermis in the center of the lesion by rather large nests, approximated close, of melanocytes in a papillary dermis widened prominently, is a nevus with some attributes of Clark's nevus and some of superficial congenital nevus, but different in several ways from both of them.

Differential diagnosis histopathologically: The possibilities basically are two: this is a true Clark's nevus or a type of nevus with features morphologic in common with Clark's nevus, but exhibiting differences striking from it histopathologically, i.e. a Clark-like nevus. The latter is the diagnosis we favor.

Clinicopathologic correlation: The lesion is elevated by virtue of the proliferation of melanocytes at the dermoepidermal junction and especially by those in the markedly widened papillary dermis; it is tan and fawn-colored because of melanin in the epidermis especially increased in amount there to varying extent; and the surface is smooth because the stratum corneum is normal.

Options for therapy predicated on knowledge of histopathologic findings: At scanning magnification, it is apparent that this lesion has been excised in its entirety. Because the features clinical are those of a nevus, in theory there was no need to remove it.

1) Many of the lesions pictured clinically in this patient are stereotypical of what Clark, coworkers, and followers of him regard as "large dysplastic nevi" diagnostic of the "dysplastic nevus syndrome." In reality, however, the large lesion shown close-up here is not a typical Clark's nevus histopathologically because of the large number and large size of nests of crowded melanocytes in a papillary dermis widened greatly by them. Moreover, those nests are situated mostly in the lower half of the markedly expanded papillary dermis. In contrast, the small pigmented lesions scattered on the trunk of this patient are authentic Clark's nevi. In short, we suggest that the large flattish pigmented lesion shown here is not a true Clark's nevus, but a close simulator of it. Certainly it is not a superficial congenital nevus because it is mostly flat clinically and the changes in the papillary dermis are confined to a discrete locus in the center of the lesion, which excludes a congenital nevus from consideration.

2) For years, Clark and his fellow workers emphasized large size as being a characteristic of "dysplastic nevi," they mentioning repeatedly that the lesions often were 1.0 cm in diameter and could be as broad as 1.5 mm or even broader. In contrast, they claimed that common acquired nevi, which they contrasted consistently with dysplastic nevi, were small, that is, about 5 mm in diameter. As time went on, the size of so-called dysplastic nevi as conceived of by Clark et al. shrunk progressively, and less and less emphasis was placed by advocates of it on those nevi being large. In fact, the number most often given in the past decade, and today, by Clark's followers for the size of so-called dysplastic nevi is 5 mm in diameter with no stress whatsoever on large size of them. The reason for the shrinkage over the course of these years is simple: many of the nevi Clark et al. were calling "dysplastic" in the 1970s and 1980s were, in reality, ones superficial congenital. Although there really is no such thing as a "common acquired nevus" per se, there being several different kinds of common melanocytic nevi, the most common acquired nevus by far is Clark's nevus. Last, the paradigm of "dysplastic nevus" versus "common acquired nevus" is simplistic in the extreme in addition to being plain wrong.

3) For more than a decade, i.e., from 1978 well into the 1990s, Clark and associates insisted trenchantly that dysplastic nevi were the most common "precursor" of melanoma and that patients with many of them were at markedly increased risk for development of melanoma. Because many of what they were calling dysplastic nevi actually were superficial congenital nevi, it is not surprising that it is now established beyond doubt [see Kaddu, et al. Melanoma Research 2002;12:271-8 and Ackerman & Harada Dermatopathology: Practical & Conceptual 2005:11(2)] that the nevus found most often in contiguity with melanoma is one congenital, not Clark's. Not only that, but it matters not a whit in regard to development of melanoma how many small Clark's nevi a patient may display, but it matters a great deal if a particular patient displays many large nevi (such as the one that engages us here) or many large superficial congenital nevi. Such a person seems truly to be at increased risk for development of melanoma.

4) Many specific types of melanocytic nevi have been identified for what they are, among them those "acquired" such as Clark's, Spitz's, and Reed's, and those "congenital" such as giant hairy, superficial, superficial and "deep," nevus spilus, and Masson's blue neuronevus. Almost certainly, other distinctive types of nevi, both "acquired" and "congenital," have yet to be characterized with precision clinically and histopathologically. We think that the nevus presented here represents one such a type.

5) In order for the subject essential under discussion in this Quiz to be elucidated and illuminated, that being the issue of the character morphologic of this particular nevus and other nevi of different kinds, among those being true Clark's, Clark-like, and superficial congenital, it is obligatory that clinicopathologic studies conducted scrupulously be undertaken and that photographs of an individual clinical nevus together with photomicrographs of the very same nevus be published side by side. Only in that way, in conjunction with the use of immediately comprehensible language (which excludes "melanocytic dysplasia" and all other terms evasive such as exemplified by the acronyms MELTUMP, SAMPUS, STUMP, and NIMP), can that matter be clarified. It is long past due that that meritorious endeavor be initiated and brought to completion successfully.

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