Introduction

Solomon et al. (1968) proposed the term epidermal nevus syndrome (ENS) to describe the association of epidermal hamartomas and extracutaneous abnormalities. Since the syndrome was first recognized, however, it has been plagued by definitional problems. In the first comprehensive review of ENS, Solomon & Esterly (1975) emphasized that, although some hamartomas have more sebaceous differentiation (i.e. nevus sebaceus), and others more epidermal differentiation (i.e. epidermal nevi), many show differentiation toward several cutaneous appendages. This concept had been previously proposed by Mehregan & Pinkus (1965) who used the term ‘organoid nevus’ to encompass the overlapping histologic features of the disorder.

In the 30 years since Solomon et al. proposed the name ‘epidermal nevus syndrome’, a second major definitional issue has arisen. Advances in genetics have led to an understanding that the cutaneous manifestations of ENS (and likely many of the extracutaneous ones as well) are due genomic mosaicism. Moreover, several different genetic abnormalities can likely lead to similar phenotypes. The appreciation of genetic heterogeneity in epidermal nevi (EN) makes it easier to comprehend the wide variety of both cutaneous and extracutaneous manifestations. Thus, although we continue to use the term ‘epidermal nevus syndrome’, it is now understood that the condition is not one disease, but rather a heterogeneous group defined by a common cutaneous phenotype: the presence of epidermal and adnexal hamartomas that are associated with other organ system involvement.

Happle (1995a) has proposed that several subsets of ENS should be differentiated from one another.