Multiple dysplastic nevi are the hallmark of AMS.
In familial AMS, the lesions usually appear during the first decade of life.
Typical features are present by the end of puberty. During adolescence, the
nevi become dysplastic and more numerous. The nevi usually are larger than
ordinary moles (6-15 mm) and have a different distribution over the body
(in sun-exposed but also in non-sun-exposed areas) such as the scalp,
buttocks, and female breasts. For the diagnosis, at least two atypical nevi
must be present, although most often they are numerous. Clinically, atypical
nevi are characterized by variable pigmentation and irregular, ill-defined
borders. Pathologic changes of the nevi include irregular borders, a mixture
of colors, indistinct margins, and a persistent macular component. If a
black area develops within a nevus, the lesion should be excised to rule out
a melanoma. Small and nondysplastic nevi appear by age 5 to 6 years.