Epidermal nevus syndromes (ENSs) are a group of rare complex disorders characterized by the presence of skin lesions known as epidermal nevi associated with additional extra-cutaneous abnormalities, most often affecting the brain, eye and skeletal systems. Epidermal nevi are overgrowths of structures and tissue of the epidermis, the outermost layer of the skin. The different types of epidermal nevi can vary in size, number, location, distribution and appearance. Neurological abnormalities that can be associated with ENSs can include seizures, cognitive impairment, developmental delays and paralysis of one side of the body (hemiparesis). Skeletal abnormalities can include abnormal curvature of the spine, malformation of the hip and abnormalities of the arms and legs (e.g., underdevelopment or absence or overgrowth of limbs). Ocular abnormalities may include cataracts, clouding (opacity) of the cornea or partial absence of tissue of the iris or retina (colobomas). Endocrine abnormalities such as vitamin D-resistant rickets have been associated with Schimmelpenning syndrome. The specific symptoms and severity of ENSs can vary greatly from one person to another. Most ENSs occur randomly for no apparent reason (sporadically), most likely due to a gene mutation that occurs after fertilization (postzygotic mutation) and is present in only some of the cells of the body (mosaic pattern).
The term "epidermal nevus syndrome" has generated significant controversy and confusion in the medical literature. Originally, the term was used to denote a disorder that was actually several different disorders erroneously grouped together. In the recent past, the term was used to denote a specific disorder now known as Schimmelpenning syndrome. However, the term epidermal nevus syndrome could be correctly applied to several different disorders. Therefore, the umbrella term "epidermal nevus syndromes" now represents a group of distinct disorders that have in common the presence of one of the various types of epidermal nevi. However, there is so far no general agreement how to classify the types of this diverse group of disorders, adding to the confusion within the medical literature. These disorders are quite different from one another and are not "variants" of each other as is sometimes mistakenly stated in the medical literature. In the future, as the genetic molecular basis of these disorders is better understood, the classification may change or expand. This report follows the classification from a review by Happle (J Am Acad Dermatol 2010).
Two other terms that have been used to describe ENSs are "organoid nevus syndrome" and "keratinocytic nevus syndrome". However, it is inappropriate to use these terms to denote a single disorder or interchangeably with epidermal nevus syndromes. Organoid nevus syndrome is a general term that could be applied to at least five different types of ENS. Keratinocytic nevus syndrome is a general term that could be applied to four different types of ENS.
NORD has individual reports on specific ENSs including Schimmelpenning syndrome, Proteus syndrome, and CHILD syndrome.