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 Table of Contents  
Year : 2018  |  Volume : 5  |  Issue : 2  |  Page : 136-137

Pseudomelanoma of the nail plate: A new entity based on a new phenomenon

1 Department of Dermatology, Rutgers-New Jersey Medical School, Newark, NJ, USA
2 Department of Plastic Surgery, Rutgers-New Jersey Medical School, Newark, NJ, USA

Date of Web Publication19-Dec-2018

Correspondence Address:
Dr. William Clark Lambert
Department of Dermatology, Rutgers-New Jersey Medical School, Newark, NJ
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijdpdd.ijdpdd_36_18

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How to cite this article:
Lambert WC, Patel S, Behbahani S, Lee E. Pseudomelanoma of the nail plate: A new entity based on a new phenomenon. Indian J Dermatopathol Diagn Dermatol 2018;5:136-7

How to cite this URL:
Lambert WC, Patel S, Behbahani S, Lee E. Pseudomelanoma of the nail plate: A new entity based on a new phenomenon. Indian J Dermatopathol Diagn Dermatol [serial online] 2018 [cited 2020 Oct 31];5:136-7. Available from: https://www.ijdpdd.com/text.asp?2018/5/2/136/247870


A pseudomelanoma is a lesion that clinically and/or histologically appears to be a melanoma but is, in fact, benign.[1],[2] The most common type of pseudomelanoma, also known as a recurrent melanocytic nevus, commonly occurs on the back of women under the age of 40 years; this recurrence occurs on an average of 6 months after excision.[2],[3] A rarer type of pseudomelanoma consists of a cellular blue nevus particularly one on the lower extremity and especially one that has undergone benign metastasis to an inguinal lymph node.[4] Treatment of a pseudomelanoma of either type is resection with submission of tissue for pathological analysis.[1],[4]

A 16-year-old Hispanic male presented with a slow-growing pigmented lesion at the base of the right thumbnail. The lesion began with a linear streak of nail pigmentation, which gradually became more irregular and ill-defined. This clinical appearance was highly suggestive of a melanoma. The whole nail was avulsed and submitted for pathology. Hundreds of pathological sections were analyzed in total. On specific histological sections [Figure 1], [Figure 2], [Figure 3], dendritic melanocytes were found trapped within the nail. These dendritic melanocytes had originated from a benign clear cell acanthoma present in the nail lunula. During the differentiation of the clear cell acanthoma tissue into the nail plate, these dendritic melanocytes became atypical and formed the pseudomelanoma lesion. The lesion did not show any malignant features.
Figure 1: Case 1. Atypical melanocytes are observed proliferating within the nail plate (H and E, ×310)

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Figure 2: Higher power image showing atypical melanocytes within the nail plate (H and E, ×976.5)

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Figure 3: Clear cell acanthoma within the lunula colonized by dendritic melanocytes (Melan A, ×310)

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We have described a pseudomelanoma for the first time occurring in the nail plate. The term pseudomelanoma has been applied to a recurrent melanocytic nevus following excision or to a dysplastic cellular blue nevus. In the former case, disruption from the nevus resection causes the remaining nevus tissue to proliferate and become atypical; this describes the first type of pseudomelanoma. In the latter case, atypia occurs within a benign lesion. This second type of pseudomelanoma is especially apt when this nevus undergoes localized “benign metastasis” to a regional lymph node.

Here, we propose a third type of a pseudomelanoma generated by anoxia. Since the nail plate is physiologically anoxic, the dendritic melanocytes become chronically exposed to the anoxic stratum corneum of the nail plate. Over time, these dendritic melanocytes assumed an atypical appearance, which led to the formation of the pseudomelanoma.

Note that nevi that can recur as a malignant melanoma. However, these cases have been shown to have malignant pathological changes before the resection of the lesion.[1] In case of point, resection of the nevus has not been shown to induce transformation into malignancy.[1] Pathological analysis of the original nevus can guide management as benign pathological features can reassure patients that a recurrence will also be benign.[1]

The term pseudomelanoma should also be applied to melanocytic lesions of this type involving the nail plate. In this case, the melanocytes are generated by another neoplasm and subsequently undergo atypia after exposure to the anoxic nail plate. Therefore, such atypia may arise from three sources: recurrent proliferation after excision, blue nevi, and anoxia.


We would like to thank Yin Zhiwei, MD, Department of Pathology at University Hospital, Newark, NJ, for working on the processing of this specimen. We did not receive any other support from any outside sources.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Fox JC, Reed JA, Shea CR. The recurrent nevus phenomenon: A history of challenge, controversy, and discovery. Arch Pathol Lab Med 2011;135:842-6.  Back to cited text no. 1
King R, Hayzen BA, Page RN, Googe PB, Zeagler D, Mihm MC Jr., et al. Recurrent nevus phenomenon: A clinicopathologic study of 357 cases and histologic comparison with melanoma with regression. Mod Pathol 2009;22:611-7.  Back to cited text no. 2
Castagna RD, Stramari JM, Chemello RM. The recurrent nevus phenomenon. An Bras Dermatol 2017;92:531-3.  Back to cited text no. 3
Lambert WC, Brodkin RH. Nodal and subcutaneous cellular blue nevi. A pseudometastasizing pseudomelanoma. Arch Dermatol 1984;120:367-70.  Back to cited text no. 4


  [Figure 1], [Figure 2], [Figure 3]


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