Dysplastic nevi are associated with an increased risk for malignant melanoma especially in melanoma kindreds. A histologic score can be used to grade the level of atypia seen microscopically in clinically dysplastic nevi. The correspondence between the histologic and clinical diagnosis of dysplasia is seen best in persons beyond 20 years of age with lesions from the trunk.


Histologic Features of Dysplastic Nevi


Melanocytic proliferation

(1) Melanocytes are conspicuous even at low magnification

(2) There is a proliferation of melanocytes along the base of closely spaced rete ridges of variable but relatively uniform length.

(3) The melanocytes may form a complete, lentiginous carpet covering the tips of the dermal papillae.

(4) If the layer of melanocytes is thick, there may be fusion of proliferating cells across adjacent rete ridges with or without nest formation.

(5) The lateral margins of melanocytic proliferation are characteristically ill-defined, with a trail of melanocytes fading gradually away from the central portions of the nevus.


Host response features:

(1) papillary dermal collagen:

(1a) distinctive bands of dense homogeneous collagen outline the base of the epidermis (concentric fibrosis)

(1b) closely apposed ribbons forming curvilinear stacks beneath the tips of rete ridges (lamellar fibrosis)

(2) lymphocytic infiltration in the papillary dermis


Cytologic features:

(1) increased cell diameter

(2) central displacement of the nucleus

(3) nuclear hyperchromatism

(4) cellular or nuclear pleomorphism


Histologic Score



(1) extent of melanocytic hyperplasia

(2) cytologic characteristics

(3) degree of lymphocytic infiltration




extent of melanocytic hyperplasia

hyperplasia confined to lateral epidermal margins of the nevus



hyperplasia evident across much or all of the epidermal base of the nevus



hyperplasia extensive, forming nests and/or a thick layer with fusion across rete ridges


cytologic characteristics

melanocytes slightly enlarged, but otherwise unremarkable



melanocytes slightly enlarged, with appreciable cytologic and/or nuclear pleomorphism



melanocytes moderately enlarged with or without cytologic and nuclear pleomorphism


lymphocytic infiltration in the dermis

none, minimal, mild



moderate, severe (easily seen when scanning at low power)



score for atypia =

= (points for extent of melanocytic hyperplasia) + (points for cytologic characteristics) + (points for degree of lymphocytic infiltration)



• minimum score: 2

• maximum score: 7

• The higher the score, the greater the degree of histologic atypia.


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