Cutaneous Melanoacanthoma Workup

Updated: Apr 05, 2021
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Dirk M Elston, MD  more...
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Workup

Laboratory Studies

Laboratory studies are not required for melanoacanthomas.

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Imaging Studies

Imaging studies are not required for melanoacanthomas.

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Procedures

Simple shave biopsy or excision, depending on the site of the melanoacanthoma, may be performed for diagnostic purposes. Because the lesions are epidermal and superficial, excision of the dermis and subcutis underlying a melanoacanthoma is not required or recommended.

Dermatoscopic features have been described, [27] including comedolike openings, fat fingers, and irregularly distributed dots. Comparison of these features between melanoacanthomas and melanoacanthomalike melanomas showed they may overlap clinically in appearance and on dermoscopy. [33] It is among the most frequent benign tumors that may have dermatoscopic characteristics suggestive of malignancy. [34] Reflectance confocal microscopy evaluation of melanoacanthoma may show features suggestive of a nodular melanoma, [35] with dendritic pagetoid cells. [36]

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Histologic Findings

Microscopic examination of cutaneous melanoacanthoma reveals a benign acanthoma composed of keratinocytes and dendritic melanocytes. Acanthosis, hyperkeratosis, parakeratosis, papillomatosis, and small horn pearls may be seen. Large dendritic melanocytes with abundant melanin granules are spread throughout the lesion. Note the image below.

Photomicrograph of cutaneous melanoacanthoma. Larg Photomicrograph of cutaneous melanoacanthoma. Large polydendritic melanocytes are seen at all levels of the epidermis. Acanthosis, hyperkeratosis, and slight papillomatosis are also present (hematoxylin and eosin stain, original magnification X139).

Cytologic atypia is not a feature of the melanocytes or keratinocytes in a melanoacanthoma. Two types of melanoacanthomas are described: a diffuse type in which melanocytes are unevenly scattered throughout the lesion and a clonal type in which melanocytes and keratinocytes are clustered in small nests. [13]

Electron microscopic studies reveal that the transfer of melanin from these highly dendritic melanocytes to neighboring keratinocytes is either partially or, in some cases, completely disrupted. [37] Immunoprecipitation assays and immunofluorescent studies show that melanoacanthoma is unrelated to malignant melanoma. [38, 39]

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