Critical analysis of histologic criteria for grading atypical (dysplastic)melanocytic nevi

Low concordance in grading atypical (dysplastic) melanocytic nevi (AMN) has been reported, and no systematic evaluation is available. We studied 123 A MN with architectural and cytologic atypia (40 associated with atypical-mol e syndrome), classified according to standard criteria by 3 independent obs ervers. Histologic variables included junctional and dermal symmetry latera l extension, cohesion and migration of epidermal melanocytes, maturation, r egression, nuclear features nuclear grade, melanin, inflammatory infiltrate location, and fibroplasia.;AMN (43 junctional and 80 compound) were graded mild (31), moderate (61), and severe (31). AMN-severe correlated with 3 or more nuclear abnormalities (especially pleomorphism, heterogeneous chromat in, and prominent nucleolus) and absence of regression, mixed junctional pa ttern, and suprabasilar melanocytes on top of lentiginous hyperplasia. AMN- severe diagnostic accuracy was 99.5% using these criteria, but only the abs ence of nuclear pleomorphism differentiated AMN-mild from AMN-moderate. No architectural features distinguishing AMN-mild from AMN-moderate were selec ted as significant by the discriminant analysis. AMN from atypical-mole syn drome revealed subtle architectural differences, but none were statisticall y significant in the discriminant analysis. Histologic criteria can reliabl y distinguish AMN-severe but fail to differentiate AMN-mild from AMN-modera te. AMN from atypical-mole syndrome cannot be diagnosed using pathologic cr iteria alone.