The term “atypical nevus” or “atypical mole” has supplanted “dysplastic nevus.” The diagnosis of atypical moles is made clinically and not histologically. 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, for which recreational sun exposure is a primary risk in nonfamilial settings. There is an increased risk of melanoma in 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 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) require closer attention, since their risk of developing single or multiple melanomas approaches 50% by age 50.
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.)
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.)
et al; Pigmented Lesion Subcommittee, Melanoma Prevention Working Group. Risk of subsequent cutaneous melanoma in moderately dysplastic nevi excisionally biopsied but with positive histologic margins. JAMA Dermatol. 2018;154:1401.
et al. Melanoma risk stratification of individuals with a high-risk naevus phenotype—a pilot study. Australas J Dermatol. 2019;60:e292.