Giant Congenital Melanocytic Nevus
National Organization for Rare Disorders, Inc.
It is possible that the main title of the report Giant Congenital Melanocytic Nevus is not the name you expected.
Congenital melanocytic nevi (CMN) are visible pigmented (melanocytic) proliferations in the skin that are present at birth. CMN are benign, tumor-like malformations resulting from faulty development of pigment cell (melanocyte) precursors in the embryo, and composed of an abnormal mixture of skin elements. Defined areas of these melanocytic proliferations cover surfaces at the base of the epidermis ranging from a few millimeters in diameter to large sectors of the body. In the larger forms, the CMN (single or multiple) also extend(s) vertically into the deeper dermis and more rarely, into the hypodermis or even subcutaneous tissues. The most superficial component of the CMN is the most highly pigmented, conferring brown-to-black shades to the overlying epidermis. CMN are usually classified according to their predicted largest diameter in adulthood, as if they were circular (predicted adult diameter or PAS). The most used classification assigns small CMN as less than 1.5 cm PAS, medium sized CMN between 1.5 to 19.9 cm, and large CMN 20 cm or greater. CMN measuring 50 cm or larger in PAS have been referred to as ‘giant congenital melanocytic nevi'.
CMN can be light brown to black patches or plaques, can present in variable ways, and cover nearly any size surface area or any part of the body. The incidence of CMN seems to be independent of skin color or other ethnic factors. Small to medium CMN are predicted to occur in more than one in a hundred births. Large and especially giant CMN, exceeding a predicted diameter at adult age of at least 20 cm on the body, form a much rarer subset, with prevalence estimated at around 1 in 50,000 births. Non-pigmented or small incipient congenital lesions can also be present - these are known as "tardive"; the emergence of so-called "satellite" nevi throughout the first few years of life in conjunction with larger CMN probably reflects the postnatal maturation of such precursors. On occasion, even a primary CMN can appear in a tardive manner. Treatment options currently are exclusively surgical. Neurocutaneous melanocytosis, cited in earlier literature as neurocutaneous melanosis (NCM), is a neurological and cutaneous disorder characterized by abnormal aggregations of nevomelanocytes within the central nervous system and the skin. NCM is a complication of the larger forms of CMN, or multiple smaller CMN, in a fraction of patients. Recent studies find the incidence of symptomatic and asymptomatic NCM together to range between 5 and 15 % of all persons with large and giant CMN. Melanoma develops in an estimated 1-2% of patients with LCMN or NCM, more frequently and at earlier ages than in the general population.
The first recorded descriptions of children with large CMN date from observations published by the Count of Buffon before the French Revolution. Other giant, sometimes rugous CMN were described in the early 19th century.
CMN tend to grow in a proportional fashion to the child's growth; occasionally growth appears out of proportion to the child during periods of particularly rapid growth such as early infancy. A new size/color/texture classification, recently developed by Marghoob, Krengel and other experts in the field, may eventually help in better predicting patients at the greatest risk for developing melanoma or neurological disease by more reproducibly classifying similar patients. Nomograms can assist clinicians in easily determining the PAS of a nevus examined at any point during childhood.
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Nevus Outreach, Inc.
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Last Updated: 2/14/2013
Copyright 2013 National Organization for Rare Disorders, Inc.
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