The term “atypical nevus” or “atypical mole” has supplanted “dysplastic nevus.” The diagnosis of atypical moles is made clinically and not histologically, and moles should be removed only if they are suspected to be melanomas. Dermoscopy by a trained clinician may be a useful tool in the evaluation of atypical nevi. Clinically, these moles are large (6 mm or more in diameter), with an ill-defined, irregular border and irregularly distributed pigmentation (Figure 6–2) (eFigure 6–3). It is estimated that 5–10% of the white population in the United States has one or more atypical nevi, and recreational sun exposure is a primary risk for the development of atypical nevi in nonfamilial settings. Studies have defined an increased risk of melanoma in the following populations: patients with 50 or more nevi with one or more atypical moles and one mole at least 8 mm or larger, and patients with any number of definitely atypical moles. These patients should be educated in how to recognize changes in moles and be monitored regularly (every 6–12 months) by a clinician. Kindreds with familial melanoma (numerous atypical nevi and a family history of two first-degree relatives with melanoma) deserve even closer attention, as the risk of developing single or even multiple melanomas in these individuals approaches 50% by age 50.
Atypical mole (nevus). (Reproduced, with permission, from Bondi EE, Jegasothy BV, Lazarus GS [editors]. Dermatology: Diagnosis & Treatment. Originally published by Appleton & Lange. Copyright © 1991 by The McGraw-Hill Companies, Inc.)
Atypical (dysplastic) nevus on the chest. Note irregular border and variegation in color. (Used, with permission, from Richard P. Usatine, MD, in Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley H. The Color Atlas of Family Medicine, 2nd ed. McGraw-Hill, 2013.)
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