Skin Diseases

Skin Diseases

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Clark Melanocytic Nevus (Dysplastic Melanocytic Nevus, Atypical Nevus)

Clark melanocytic nevi (CMN) are a special type of acquired, circumscribed, pigmented lesions that represent disordered proliferations of variably atypical melanocytes. CMN arise de novo or as part of a compound melanocytic nevus. CMN are clinically distinctive from common acquired nevi: larger and more variegated in color, asymmetric in outline, irregular borders; they also have characteristic histologic features. CMN are regarded as potential precursors of superficial spreading melanoma and also as markers of persons at risk for developing primary malignant melanoma of the skin, within the dysplastic nevus or on "normal" skin.


Multiple loci, including 1p36 and 9p21, have been implicated in familial melanoma/dysplastic nevus syndrome. The abnormal clone of melanocytes can be activated by exposure to sunlight. Immunosuppressed patients (renal transplantation) with dysplastic nevi have a higher incidence of melanoma. Dysplastic nevi favor the exposed areas of the skin, and this is related to the degree of sun exposure. Dysplastic nevi may, however, occur on the covered areas (e.g., hairy scalp or groin).


Atypical nevi can occur anywhere on the body, and usually begin to appear at puberty. They may however, be more common in sun-exposed areas, the back, and the legs.

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