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Dermatopathology: Practical & Conceptual April - June 2008
5. New Heights: “Animal-type” melanoma and entities related to it (Part I): Evolution of a concept
François Milette, M.D.
A. Bernard Ackerman, M.D.
Contents of Part I
I. Melanosis in horses and men? (Dick, 1832)
II. A précis of equine melanotic disease (Levene, 1971)
III. Melanoma arising in “blue nevi”? (Darier, 1925)
IV. Diffuse mesodermal pigmentation? (Carleton and Biggs, 1948)
V. Melanotic disorders in horses and men? (Levene, 1979)
VI. Pilar neurocristic hamartoma? (Tuthill, Clark, and Levene, 1982)
VII. Malignant melanoma arising in a blue nevus? (Pathy, Helm, Elston, Bergfeld and Tuthill, 1993)
VIII. Cutaneous malignant melanotic neurocristic tumor arising in neurocristic hamartoma? (Pearson, Weiss, Headington, 1996)
IX. Malignant melanoma with prominent pigment synthesis: “Animal-type melanoma”? (Crowson, Magro, Mihm, 1999)
X. Animal type melanoma? (Requena, de la Cruz, Moreno, Sangueza, Requena, 2001)
XI. Animal-type melanoma? (Kazakov, Rütten, Kempf, Michal, 2004)
XII. In the textbooks?
XIII. Melanomas in horses as described in veterinary medicine literature? (Valentine, 1995; Seltenhammer, 2004)
VI. Pilar neurocristic hamartoma? (Tuthill, Clark, and Levene, 1982)
In 1982, Tuthill, Clark, and Levene presented what they termed "pilar neurocristic hamartoma" in an 18-year-old woman (
) whom they had followed for 18 months. [
] When she was 8, a lesion the size of a coin was noted on her chest, it not being known whether it had been in place at birth. The lesion had enlarged slowly, new papules appeared progressively in fashion accelerated, and, in time, it attained a size 9.5 x 10 cm. By age 18, multiple, slightly keratotic, pigmented papules were observable on the chest.
Figures 3 and 4 reproduced from the article by Tuthill et al.[
]. Our comment: The presence of melanocytes in association perifollicular reveals nothing else than the nature congenital of the lesion.
Two biopsies were performed, and changes in sections of tissue from the specimens harvested were interpreted variously by three different pathologists as follows: (1) intradermal nevus, (2) blue nevus, and (3) hamartomatous malformation of neural crest origin.
The lesion was excised
but recurred at the margin of a skin graft. The site affected was re-excised, and no persistence local had been identified after 18 months.
Although the lesion "simulated a combined intradermal and superficial blue nevus" histopathologically, the attention of the authors was arrested by the fact that in many foci the cells housing melanin appeared to be congregated around the inferior segment of hair follicles. Moreover, studies ultrastructural revealed what the authors claimed were signs of schwannian differentiation.
The coworkers noted attributes in the lesion, as it was assessed by microscopy conventional, that reminded them of two entities different from one another, namely, melanotic disease in horses, and the plaque-type of blue nevus in humans. Concerning equine melanotic disease the authors made these remarks:
"Important differences [between the equine disease and the lesion studied by them] are the lack of graying and the localized nature of the disorder in our patient. Also in man, unlike the horse, the development and function of the eccrine sweat gland are independent from the hair follicle."
The collaborators seemed to have a need irrepressible to find differences between the disease in their patient and that in horses—so they found some! Concerning plaque-type blue nevus in humans, they made these comments:
"Some previously reported plaque-type blue nevi, on histologic examination have shown peri-appendageal accumulation of pigmented spindle cells BUT THIS WAS PART OF A DIFFUSE PROCESS WITH SECONDARY CONDENSATION [emphasis ours] . . . Some of these [cases] at physical examination have shown multiples papules and nodules but none were described as discretely peripilar."
The criteria employed by Tuthill et al. for diagnosing pilar neurocristic hamartoma are these:
Discretely perifollicular (incorrectly said to be "peripilar") aspect clinical of papules and nodules.
Periappendageal condensation of pigmented spindle cells on examination histopathologic, that is, there was no component diffuse.
But the patient developed a metastasis in which
"The pigment containing spindle cells [were] forming a dermal nodule that was larger than any seen in earlier specimens."
What was going on in the lesion in this patient? Did a malignant melanoma develop in it? Did a benign "secondary" component diffuse appear? What was the character fundamental of the "dermal nodule." nevus or melanoma? No answer is provided by the authors.
In our view, the criteria set forth by Tuthill et al. for diagnosis of pilar neurocristic hamartoma are not compelling because periadnexal condensation of pigmented spindle cells only informs of the likely nature congenital of a lesion melanocytic, no matter whether or not the lesion was apparent clinically at birth. Beyond that, distribution periadnexal conveys nothing more illuminating about the character of the lesion. Moreover, how is it possible, on the basis of an image static observed through a microscope to distinguish a
"peri-appendageal condensation secondary to a diffuse component" from a "diffuse component secondary to an extending peri-appendageal condensation"?
Any answer to that question is pure supposition.
Despite these limitations serious, Tuthill and associates went on to infer the following:
"Within this spectrum of disease, only our patient's disorder has shown a discrete peripilar arrangement of cells similar to the equine disease, and because of this, we BELIEVE [emphasis ours] it deserves separation and recognition."
In brief, it all is a matter of belief! It is as one wishes it to be. There are differences important when one needs them (as Carleton and Biggs did in 1948 [
]) and similarities of consequence when one requires them (as Tuthill et al. did [
Having seen by examination ultrastructural attributes schwannian in their lesion, the authors then proceeded to justify the new designation proposed by them, they doing it in this long sentence:
"It is because of this combined differentiation toward two separate neural-crest-derived structures that we believe [emphasis ours] our patient's lesion is a hamartoma of neural crest origin and because of the prominent perifollicular arrangement, we wish to designate it "pilar neurocristic hamartoma."
Does the presence of differentiation schwannian exclude the possibility of blue nevus? It does not—if, in reality, there is such a single entity distinct. Furthermore, what, exactly, are the criteria histopathologic for identifying schwannian differentiation and, are nevi, including those dubbed "blue," truly congenital neoplasms or hamartomas? No answers to those inquiries legitimate were provided by the fellow workers.
For us, the morphologic findings in this 18-year-old woman are much like those in Patient 1 of Darier, [
] a plaque-type congenital nevus of the kind referred to as "blue." The progression ever more accelerated of it and the recurrence clinical of it give pause, but, because no long-term follow-up is available, we are forced to suspend judgment about whether or not a melanoma came to develop in association with the original condition melanocytic.
In sum, we contend that Tuthill et al. succumbed to wishful thinking in the presentation of their ideas and, in the process, they failed to bring to the matter before them a mentality critical, logical, and incisive, all of which combined to bring them to the concept and the appellation of "pilar neurocristic hamartoma." Sad to say, there is no evidence that it is "pilar," i.e., related to hair, "neurocristic," i.e., pertaining to the neural crest, or a hamartoma, i.e., a hodge-podge of elements in arrangement abnormal but present normally at a particular site. Even were there evidence on behalf of relation to the adnexa folliculosebaceous, origin neurocristic, and nature hamartomatous, the hamartoma itself surely would not be pilar, but rather elements neurocristic in it would be distributed in a manner perifollicular.
In our opinion, the lesion reported on by Tuthill et al. is best interpreted as a plaque-type blue nevus within which a melanoma could have developed, just as it could in any "benign" proliferation of melanocytes, be it congenital or acquired.
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